Mechanical Interview Questions

 Mechanical Interview Questions contains questions about

1. Define maintenance?

Maintenance is the routine and recurring process of keeping a particular machine or asset in its normal operating conditions So that it can deliver the expected performance or service without any loss or damage.

2. 1 hp how much watt?

746.2Watt

3. Define reliability?

Reliability is defined as the probability that a component /system, when operating under given condition, will perform its intended functions adequately for a specified period of time. It refers to the like hood that equipment will not fail during its operation.

4. State the benefits of reliability analysis in industries?

The main advantages of imposing reliability requirements are increased productivity and reductions in forced outage equipment due to planned maintenance activity.

5. What is the need for drafting?

Drafting is the allowance give to casting process.it also used to remove the casting from mould without damage of corners.

6. What is the difference between BSP thread and BSW thread?

The British Standard Pipe thread (BSP thread) is a family of standard screw thread types that has been adopted internationally for interconnecting and sealing pipe ends by mating an external (male) with an internal (female) thread.

British Standard Whitworth (BSW) is one of a number of imperial unit based screw thread standards which use the same bolt heads and nut hexagonal sizes.

7. What is basic difference between impulse turbine and reaction turbine?

In impulse turbine, jet is used to create impulse on blades which rotates the turbine and in reaction turbine, no jet is used pressure energy is converted into kinetic energy.

In impulse turbine fluid enter& leave with same energy ,but in reaction turbine fluid enter with pressure energy & leaves with kinetic energy

In impulse turbine all the pressure drops in nozzle only & in reaction turbine pressure drops both fixed & moving blades.the difference is due to blade profiles.

8. What is refrigerant?

Any substance that transfers heat from one place to another, creating a cooling effect. water is the refrigerant in absorption machines.

9. The amount of carbon present in Cast Iron

Carbon is basically present in the form of cementite in cast iron.Its percentage lies in the range of 2.03-6.67(% by weight of cementite for Cast Iron.If the amount is less than the above range than it is stainless steel.

10. What are the loads considered when designing the Nut and Bolts?

Shear Loads & crushing loads

11. What is the Difference between a Generator and Inverter?

An inverter is only effective if there is already a source of electrical energy. It cannot generate its own. It can simply convert electrical energy that is already there. 

On the other hand, a traditional generator cannot make AC current into DC current.

12. What is the Difference between Quantitative and Qualitative Research?

Quantitative research involves gathering data that is absolute, such as numerical data, so that it can be examined in as unbiased a manner as possible.

Qualitative research may yield stories, or pictures, or descriptions of feelings and emotions. The interpretations given by research subjects are given weight in qualitative research, so there is no seeking to limit their bias. At the same time, researchers tend to become more emotionally attached to qualitative research, and so their own bias may also play heavily into the results.

13. What is the importance of the Thermodynamics in the field of Mechanical Engineering?

All the mechanical engineering systems are studied with the help of thermodynamics. Hence it is very important for the mechanical engineers.

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14. Is the boiler a closed system?

Yes definitely the boiler is a closed system.

15. What is Carnot engine?

It was being designed by Carnot and let me tell you that Carnot engine is an imaginary engine which follows the Carnot cycle and provides 100% efficiency.

16. Which is the hardest compound known?

Diamond.

17. What is Hess Law?

According to the Hess law the energy transfer is simply independent of the path being followed. If the reactant and the product of the whole process are the same then same amount of energy will be dissipated or absorbed.

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18. Which has more efficiency: Diesel engine or Petrol engines?

Off course Diesel engine has the better efficiency out of two.

19. What is Bending moment?

When a moment is applied to bend an element, a bending moment exists in the element

20. What are the points in the Stress Strain curve for Steel?

Proportional limit, elastic limit or yield point, ultimate stress and stress at failure.

21. How many Joules is 1 BTU?

1 BTU is equal to 1055.056 joules.

22. What is PS?

PS is Pferdestarke, the German unit for Horsepower.

23.Explain Otto cycle.

Otto cycle can be explained by a pressure volume relationship diagram. It shows the functioning cycle of a four stroke engine. 

The cycle starts with an intake stroke, closing the intake and moving to the compression stroke, starting of combustion, power stroke, heat exchange stroke where heat is rejected and the exhaust stroke. 

It was designed by Nicolas Otto, a German engineer.

24. Explain the nomenclature of a 6203-ZZ bearing.

6 is the type code, which shows it is a single-row ball bearing, 

2 is the series, means light, 

03 is the bore, which is 17 mm and 

ZZ is the suffix meaning double shielded bearing.

25. What is Gear ratio?

It is the ratio of the number of revolutions of the pinion gear to one revolution of the idler gear.

26. What is Annealing?

It is a process of heating a material above the re-crystallization temperature and cooling after a specific time interval. This increases the hardness and strength if the material.

27. Define Torque.

Torque is defined as a force applied to an object that results in rotational motion.

28. What is Ductile-Brittle Transition Temperature?

It is the temperature below which the tendency of a material to fracture increases rather than forming. Below

this temperature the material loses its ductility. It is also called Nil Ductility Temperature.

29. What is Auto Dosing?

Auto dosing is an automated system of feeding the equipment with liquid products.

It is the ideal way to ensure the correct calibrated dose at the right time every time in auto.

30. Difference between Codes, Standards and Specifications?

1. Code is procedure of acceptance and rejection criteria.
2. Standard is accepted values and compare other with it.
3. Specification is describing properties of any type of materials.

31. What will be the position of Piston Ring?

In 180 degree angle the Top ring, Second ring and Oil ring are fixed. Position the ring approximately 1 inch gap below the neck.

32. What is Heat rate of a Power plant?

Heat rate is a measure of the turbine efficiency. It is determined from the total energy input supplied to the Turbine divided by the electrical energy output.

33. What is a Hydrostatic system?

Hydrostatics is the study of fluid bodies that are

• At rest
• Moving sufficiently slowly so there is no relative motion between adjacent parts of the body

For hydrostatic situations

• There are no shear stresses
• There are only pressure forces that act perpendicular to any surface.

It’s a closed loop hydraulic systems. It comprises of motor and pump. Here pump supplies energy to motor and motor gives return energy to pump supply.

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34. How to find a Ductile-Brittle Transition Temperature in metals?

The point at which the fracture energy passes below a pre-determined point for a standard Impact tests. 

DBTT is important since, once a material is cooled below the DBTT, it has a much greater tendency to shatter on impact instead of bending or deforming.

35. What is Hydrodynamic Cavitation?

Hydrodynamic cavitation describes the process of vaporization in a constrained channel at a specific velocity.

Bubble generation and Bubble implosion which occurs in a flowing liquid as a result of a decrease and subsequent increase in pressure.

36. Explain about Powder Technology?

Powder technology is one of the ways of making bearing material. In this method metals like bronze, Al, Fe are mixed and compressed to make an alloy.

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37. What are the points in the Stress Strain curve for Steel?

Proportional limit, elastic limit or yield point, ultimate stress and stress at failure.

38. What is the difference between Pipe and Tube?

Ex. Iron Pipe, Carbon Tube, Steel Tube etc.

Tube is defined by Outer diameter and Wall thickness (OD and WT). While Pipe is defined by Inner diameter (ID).

Example:

2 inch pipe have 2.375 inch outer diameter, where 2 inch tube have same 2 inch outer diameter.

· Tube is easily shaped by bending, where Pipe needs some mechanical work to shape it.

· Tube is tight then Pipe.

· Tube is applicable to non cylindrical sections like Square and Rectangular.

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39. How does Welding damage Eye sight?

An Electric welding arc produces Ultraviolet light and the UV light (Sun burn) will damage the retina. Welding shields or Goggles with the proper shade (Automatic shading) of lens is the best protection for welders.

Light filtering curtains and reduced reflective surfaces help protect both welders and observers in the area.

40. Explain why BCC, FCC and CPH lattice packing and features of grain structure affect the Ductility and Brittleness of parent metallic materials?

Ductility is the mechanical property of a material. (It is the material’s ability to deform under the tensile stress without fracture). 

So it is depends on the atoms how they arranged in a lattice and its grain size. 

The ability to absorb the energy of the impact and fracture resistance depends on the arrangement of the atoms in a lattice and features of grain structure.

41. Why do you have Truss Bridges?

Truss bridges carry load in tension and compression rather than bending (Self weight + The weight of vehicles crossing it + Wind loads). 

A truss has the ability to dissipate a load through the truss work. The beams are usually arranged in a repeated triangular pattern, since a triangle cannot be distorted by stress.

42. Why I-section beam is preferred for heavy loading?

Cross sectional shape I, giving many benefits. 

It is very good for giving stiffness (less deformation on loading) and to withstand higher bending moments (as a result of heavy loading) on comparison with other cross- sectional shapes of same area. 

Also, it is very easy to manufacture. It will have more moment of inertia.

43. What is difference between Center of Mass and Center of Gravity?

Both terms are same when gravity is uniform. When gravity is non-uniform following are the terms:

The center of mass is a point that acts as if all the mass was centered there (the mass on one side of the point is equal to the mass on the opposite side). If supported at the center of mass, an object will be balanced under the influence of gravity.

The center of gravity is the point at which where the sum (vector) of the gravitational forces act on an object which will be balanced on that point.

44. What is the difference between Center of Mass and Centroid?

If the material composing a body is uniform or homogeneous, the density or specific weight will be constant throughout the body, and then the centroid is the same as the center of gravity or center of mass.

Centroid: Centroid is the point, where the whole area of plane is going to be act. It is valid only for 2D problems like plane figures, square plate etc.

The center of mass is a point that acts as if all the mass was centered there (the mass on one side of the point is equal to the mass on the OPPOSITE side). 

If supported at the center of mass, an object will be balanced under the influence of gravity.

45. What are the differences between Weight and Mass?

Mass is a measure of how much matter an object has. Mass is specified in Gram or Kilograms.

Weight is a measure of how strongly gravity pulls on that matter. Force is measured in Newton’s.

F=m.g

Thus if you were to travel to the moon your weight would change because the pull of gravity is weaker there than on Earth but, your mass would stay the same because you are still made up of the same amount of matter.

46. What is the difference between Projectile motion and a Rocket motion?

A projectile has no motor/rocket on it, so all of its momentum is given to it as it is launched. An example of a projectile would be pen that you throw across a room.

A rocket or missile does have a motor/rocket on it so it can accelerate itself while moving and so resist other forces such as gravity.

In mechanics point of view projectile don’t have any particular shape it is a point mass. 

Whereas rocket has a particular shape and hence it has center of gravity situated at particular point on its body. Therefore rocket motion comes under kinetics and projectile comes under kinematics.

47. What type of cooling used in High Voltage Transformer?

The big transformers you find on power poles usually use oil as a dielectric insulator, in smaller HV transformers, like the ones in TV’s are usually filled with resin.

48. What is honing of Cylinder Liners?

The honing equipment used has been manufactured by "Chris Marine". The head of the honing device consists of four synchronized stones. 

For the initial honing diamond stones are used to break up the hardened surface in the scuffed areas. For the main honing very coarse and hard stones are used to produce a very desirable rough surface all over the liner.

The advantage, especially for the 2-stroke engines, is possibility to save the liner after a seizure, scuffing or blow-by or even to eliminate the ovality of the liner.

 Another advantage is that it is possible to machine a rough liner wall to obtain a well oiled surface.

49.What is the difference between Speed and Velocity?

Speed is scalar quantity and Velocity is a vector

– velocity has both speed and direction.

Speed is expressed as distance moved (d) per unit of time(t). 

Speed is measured in the same physical units of measurement as velocity, but does not contain an element of direction. Speed is thus the magnitude component of velocity.

50. Difference between Yield Stress and Yield Strength?

Stress is a measure of the load applied to a sample relative to a cross sectional area of the sample. Strength is a quantification of the samples ability to carry a load.

The terms "yield strength" and "yield stress" of a material are usually used interchangeably (correct or not). It is the stress which will just cause the material to plastically deform. 

If a material yields at 30,000 psi, the yield stress is 30,000 psi. If the part in question has a cross sectional area of 2 square inches, the strength at yield would be 60,000 pounds, but usually we just say the yield strength is 30,000 psi.

51. What is the difference between Yield and Ultimate tensile strength?

The yield strength is reached when the material becomes Non – linear (that is non elastic) and takes a permanent set when load is released.

Material stretches but does not break. Ultimate strength is when it breaks and is higher than yield strength.

52. What is the difference between Flexural strength and Tensile strength?

Flexural strength is resistance offered against bending. Tensile strength is resistance offered against tensile force.

53. What is the difference between Shear and Tensile strength?

Tensile Strength for a Bolt is determined by applying a Force along it long axis.

 Shear Strength for a Bolt is determined by applying a Force across its diameter, as it would be loaded in a lug joint. 

Tensile strength is strength in tension when pulling force is applied. And shear strength is strength against cutting force which is known as shear force.

54. What is the difference between Tensile strength and Tensile modulus?

Tensile strength is the ultimate capacity of the material to resist a tensile load regardless of deflection.

Tensile modulus also known as Young’s modulus is a measure of the stiffness of an isotropic elastic material. 

It is defined as the ratio of the uni-axial stress over the uni-axial strain. It is determined from the slope of a stress-strain curve traced during tensile tests conducted on a sample of the material.

55. What is OEE?

OEE means Overall Equipment Effectiveness. This terminology widely used in Total productive maintenance, which is used to calculate the effectiveness of machines in manufacturing. Basically it captures the losses of machines in production and try to improve defects on machines. Higher the OEE, more capable is the machine.

56. Why Involutes Curve used in Gear?

Involute curve is the path traced by a point on a line as the line rolls without slipping on the circumference of a circle. 

Involute curve has a contact angle between two gears when the tangents of two gears pass through the contact point without friction.

57. What is Bearing stress?

The stress which acts on the contact surface area between two members is known as Bearing stress. An example for this is the stress between nut and the washer.

58. Which is hard material Cast Iron or Mild Steel?

Cast iron. Due to the excess carbon content than mild steel it is harder. The more carbon content, the more hardness will be. 

But it reduces the weldability due to this hardness. It is brittle too.

59. What are the materials used for Sliding Wear pad?

1. Urethane-Coated Base Material Provides Optimum Sliding Surfaces for Maximum Wear Ability

2. Galvanized Steel for Backing on Head and Side Pads

3. For crane services, We use Velcro Nylon wearing pad

60. What is the difference between a Shaper machine and a Planner machine?

In Shaper machine tool is having reciprocating motion and work piece is clamped on table which is stationary. 

It is mostly suitable for light duty operation. In Shaping large cutting force is transferred to tool.

In Planer machine tool is having stationary and work piece is clamped on table which is reciprocating motion. It is mostly suitable for Heavy duty operation. In planner large cutting force is transferred to table.

61. How will you calculate the tonnage of Mechanical Press?

F = S x L x T / 1000 

F = Force in kilo Newton’s

S = shear stress of material in MPa

L = the total length of peripheries being cut/ sheared in mm

T = thickness of material in mm

62. What is the composition of Grey cast iron Grade 20?

Carbon : 3.10 – 3.25% 

Silicon : 1.75-

1.95% Manganese : 0.50 – 0.7%

Sulphur : 0.05

– 0.07% 

Phosporous : 0.04 – 0.07%

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63. What is the composition of Cast iron Grade 35?

Carbon=2.90-3.10%

Manganese=0.60- 1.00%

Silicon=1.50-1.90%

Sulphur=0.10%

Phosphorus=0.15% 

Chromium=0.30% 

Molybdenum=0.30% 

Cupper=0.25%

64. What are the super alloys?

Super alloys is an alloy that exhibits excellent mechanical strength and creep resistance at high temperatures, having good surface finish.

65. Why the Super alloys used for land- based turbines?

Super alloys are the top most alloys used for their excellent strength and corrosion

resistance as well as oxidation resistance. No other alloys can compete with these grade.

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66. What kinds of NDT methods are available?

1.Visual Inspection 

2.Microscopy inspection 

3.Radiography Test

4.Dye Penetrate technique 

5.Ultrasonic testing 

6.Magnetic Particle inspection

7.Eddy Current technology 

8.Acoustic Emission

9. Thermograph 

10.Replica Metallographic

67. What is Stress Corrosion cracking?

Stress corrosion cracking (SCC) is a process involving the initiation of cracks and their propagation, possibly up to complete failure of a component, due to the combined action of tensile mechanical loading and a corrosive medium.

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68. What is meant by D2 Material used for Die tooling?

D2 – High Carbon Cold Work Tool Steel

D2 is a high Carbon, high Chromium, Molybdenum, Vanadium, Air hardening alloy tool steel which offers good wear resistance, high surface hardness, through hardening properties, dimensional stability and high resistance to tempering effect. D2 tool steel is also suitable for vacuum hardening.

Typical Composition

C.-1.50%

Si.-0.30% Cr. -12.00%

Mo. -0.80%

V. -0.90%

69. What is Vacuum Induction Melting?

As the name suggests, the process involves melting of a metal under vacuum conditions.

Electromagnetic induction is used as the energy source for melting the metal. Induction melting works by inducing electrical eddy currents in the metal.

The source is the induction coil which carries an alternating current. The eddy currents heat and eventually melt the charge.

70. What is Bending moment?

When a moment is applied to bend an element, a bending moment exists in the element

71. Where Multi-stage pump used?

Pressure washing of Aircraft, Trains, Boats and Road vehicles as well as Spray washing of industrial parts and Electronic components.

72. What is the function of Scoop in BFP (Boiler Feed Water Pump) in Thermal Power Station?

The Function of Scoop tube is regulating the varying amount of oil level in the coupling during operation of infinite variable speed.

73. In the Thermal Power Plant why Deaerator (D/A) placed on height?

To build a Very high pressure and the temperature for a boiler feed water pump and it discharge high pressure water to the boiler.

And to provide the required Net Positive Suction Head (NPSH) for the BFW pump and to serve as a storage tank to ensure a continuous supply of feed water during rapid changes in BFP.

74. How to determine the capacity of Refrigeration system? How we use Condenser coils, Compressor, Capillarity?

To determine the Refrigeration system by test of C.O.P and use the Condenser coils, Compressor, Capillarity, based on the properties

75. In orifice why the Pressure and Temperature are decreases?

Orifice is a small hole like a nozzle. When a high pressure fluid passes through the orifice,

Pressure gets reduced suddenly and the velocity of the fluid gets increased. Also the heat transfer rate increases. 

We know that Heat transfer rate is directly proportional to the difference in temperature, Area and the Heat transfer coefficient. 

Heat transfer Coefficient remains constant for a fluid at a particular temperature.

Q= KA (T1-T2)

If the heat transfer rate increases, it seems the difference in temperature gets increased. 

There is no way in reduction of inlet temperature of the orifice. As a result, the outlet temperature of the orifice gets reduced. Hence the pressure and temperature gets reduced when it passes through orifice.

 76 What is a radial-flow turbine?

In a radial-flow turbine, steam flows outward from the shaft to the casing. The unit is usually a reaction unit, having both fixed and moving blades.

77 What are four types of turbine seals?

o Carbon rings fitted in segments around the shaft and held together by garter or retainer springs.

o Labyrinth mated with shaft serration’s or shaft seal strips.

o Water seals where a shaft runner acts as a pump to create a ring of water around the shaft. Use only treated water to avoid shaft pitting.

o Stuffing box using woven or soft packing rings that are compressed with a gland to prevent leakage along the shaft.

78. What are two types of clearance in a turbine?

o Radial – clearance at the tips of the rotor and casing.

o Axial – the fore-and-aft clearance, at the sides of the rotor and the casing.

79. What is the function of a thrust bearing?

Thrust bearings keep the rotor in its correct axial position.

80 What are some conditions that may prevent a turbine from developing full power?

o The machine is overloaded.

o The initial steam pressure and temperature are not up to design conditions.

o The exhaust pressure is too high.

o The governor is set too low.

o The steam strainer is clogged.

o Turbine nozzles are clogged with deposits.

o Internal wear on nozzles and blades.

81. What is the difference between Bolt and Screw?

The main difference was based on the load acting on it, and the size. For smaller loads, screws are enough but in case of greater-loads, bolts are to be used. 

In bolt we give centrifugal force or tangential force and screw we give axial force for driving.

82. What is the differences between gas turbine and a steam turbine?

Gas turbine works on Bryton cycle where as steam turbine works Rankine cycle.

Construction, operation of a gas turbine are entirely different to steam turbine. 

Gas turbine has a compressor to compress the combustion air, a combustion chamber to burn the fuel and a turbine section to extract the work for burning fuel.

 Steam turbine is just has a turbine section to extract the work from steam.

83. What is operating pressure?

The amount of pressure nearest the point of performing work at the output end of a pneumatic system. The system operating pressure is used to specify the capability of valves and actuators.

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84. What are the safety valves? How many on each boiler?

A valve opening automatically to relieve excessive pressure, especially in a boiler.

There are normally two to six safety valves provided in the drum depending upon the capacity.

The super heater outlet will have one to three safety valves on either side of the boiler. There will be an electromatic relief valve on the super heater pipe in addition. 

This valve will be set at lower pressure than the lowest set safety valve on the super heater.

The reheater pipes both at the inlet and outlet side will also have safety valves which can range from two to eight both in the inlet and outlet of the reheater put together.

85. What is a sentinel valve?

Sentinel valves are simply small relief valves installed in some systems to warn of impending over pressurization. 

Sentinel valves do not relieve the pressure of the system. If the situation causing the sentinel valve to lift is not corrected, a relief valve (if installed) will lift to protect the system or component. 

If a relief valve is not installed, action must be taken quickly to secure the piece of equipment or system to reduce the pressure.

86. What is the function of Hydrogen seals work on a generator?

Provide a seal between the generator housings and rotor shaft to maintain the pressurized hydrogen gas inside the generator. 

Also, provides a trap-vent system to prevent the release of hydrogen into the turbine generator lube oil system and building atmosphere.

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87. How is the excess discharge pressure prevented?

Pressure relief valves on the discharge side of each seal oil pump relieves back to seal oil system.

88. Which two seal oil pumps are driven from the same motor?

Main seal oil pump and re-circular seal oil pump; both are driven by Main seal oil pump motor.

89. When does Emergency Seal Oil Pump automatically start?

When its pressure switch senses Main Seal Oil Pump discharge pressure reduced to 78 PSI.

90. What is the consequence of not maintaining hydrogen (or air) pressure in generator casing at a value above atmospheric pressure when seal oil system is in service?

Failure to do so will cause excessive seal oil to be drawn into the generator.

91. What is a stage in a steam turbine?

In an impulse turbine, the stage is a set of moving blades behind the nozzle. 

In a reaction turbine, each row of blades is called a "stage." 

A single Curtis stage may consist of two or more rows of moving blades.

92. What is a diaphragm?

Partitions between pressure stages in a turbine’s casing are called diaphragms. They hold the vane-shaped nozzles and seals between the stages. 

Usually labyrinth-type seals are used. One-half of the diaphragm is fitted into the top of the casing, the other half into the bottom.

93. What are the two basic types of steam turbines?

o Impulse type.

o Reaction type.

94. What are topping and superposed turbines?

Topping and superposed turbines arc high- pressure, non-condensing units that can be added to an older, moderate-pressure plant. 

Topping turbines receive high-pressure steam from new high-pressure boilers.

The exhaust steam of the new turbine has the same pressure as the old boilers and is used to supply the old turbines.

95. What is a combination thrust and radial bearing?

This unit has the ends of the Babbitt bearing extended radically over the end of the shell. 

Collars on the rotor face these thrust pads, and the journal is supported in the bearing between the thrust collars.

96. What is important to remember about radial bearings?

A turbine rotor is supported by two radial bearings, one on each end of the steam cylinder. 

These bearings must be accurately aligned to maintain the close clearance between the shaft and the shaft seals, and between the rotor and the casing.

If excessive bearing wear lowers the he rotor, great harm can be done to the turbine.

97. How many governors are needed for safe turbine operation? Why?

Two independent governors are needed for safe turbine operation. One is an over speed or emergency trip that shuts off the steam at 10 percent above running speed (maximum speed). 

The second, or main governor, usually controls speed at a constant rate; however, many applications have variable speed control.

98. How is a fly ball governor used with a hydraulic control?

As the turbine speeds up, the weights are moved outward by centrifugal force, causing linkage to open a pilot valve that admits and releases oil on either side of a piston or on one side of a spring-loaded piston. 

The movement of the piston controls the steam valves.

99. What is meant by critical speed?

It is the speed at which the machine vibrates most violently. 

It is due to many causes, such as imbalance or harmonic vibrations set up by the entire machine. 

To minimize damage, the turbine should be hurried through the known critical speed as rapidly as possible. 

(Caution, be sure the vibration is caused by critical speed and not by some other trouble).

100. How is oil pressure maintained when starting or stopping a medium-sized turbine?

An auxiliary pump is provided to maintain oil pressure. Some auxiliary pumps are turned by a hand crank; others are motor-driven. 

This pump is used when the integral pump is running too slowly to provide pressure, as when starting or securing a medium-sized turbine.

101. Besides lubrication, what are two functions of lubricating oil in some turbines?

In larger units, lube oil cools the bearings by carrying off heat to the oil coolers. Lube oil in some turbines also acts as a hydraulic fluid to operate the governor speed-control system.

102. Do you stop cooling-water flow through a steam condenser as soon as the turbine is slopped?

You should keep the cooling water circulating for about 15 mill or more so that the condenser has a chance to cool down gradually and evenly. 

Be sure to have cooling water flowing through the condenser before starting up in order to prevent live steam from entering the condenser unless it is cooled. Overheating can cause severe leaks and other headaches.

103.  How can the deposits be removed?

o Water soluble deposits may be washed off with condensate or wet steam.

o Water insoluble deposits are removed mechanically after dismantling the turbine.

o Experience shows that water soluble deposits are embedded in layers of water-insoluble deposits. And when the washing process is carried out, water soluble parts of the deposit dissolve away leaving a loose, friable skeleton of water- insoluble deposits which then break loose and wash away.

104. How can the fatigue damage on high- pressure blades be corrected?

Fatigue-damage on high-pressure blades arises due to vibration induced by partial-arc admission. This can be corrected by switching over to full arc admission technique.

105. How will you detect that misalignment is the probable cause of excessive vibration?

o Coupling to the driven machine is to be disconnected.

o The turbine is to be run alone.

o If the turbine runs smoothly, either misalignment, worn coupling or the driven equipment is the cause of the trouble.

106. In which part of the steam turbine does corrosion fatigue occur?

In the wet stages of the LP cylinder.

107 In which part of the steam turbine does stress corrosion cracking (SCC) occur?

In the wet stages of the low-pressure turbine.

108. In which zone of steam turbines has temperature-creep rupture been observed?

Damage due to creep is encountered in high temperature (exceeding 455°C) zones. That is, it has been found to occur in the control stages of the high-pressure and intermediate-pressure turbines where steam temperature sometimes exceed 540°C.

In the reheat stage, it has been observed that creep has caused complete lifting of the blade shroud bands.

109. What are the types of thrust bearings?

o Babbitt-faced collar bearings

o Tilting pivotal pads

o Tapered land bearings

o Rolling-contact (roller or ball) bearings

110. What are the types of turbine seals?

o Carbon rings fitted in segments around the shaft and held together by garter or retainer springs.

o  Labyrinths mated with shaft serrations or shaft seal strips.

o  Water seals where a shaft runner acts as a pump to create a ring of water around the shaft. Use only treated water to avoid shaft pitting.

o  Stuffing box using woven or soft packing rings that are compressed with a gland to prevent leakage along the shaft.

111. What are the basic causes of the problem of rotor failure?

 Normal wear.

 Fatigue failure due to high stress.

 Design deficiency.

 Aggressive operating environment

112. What are the differences between impulse and reaction turbines?

 The impulse turbine is characterized by the fact that it requires nozzles and that the pressure drop of steam takes place in the nozzles.

 The reaction turbine, unlike the impulse turbines has no nozzles, as such. It consists of a row of blades mounted on a drum. 

The drum blades are separated by rows of fixed blades mounted in the turbine casing. These fixed blades serve as nozzles as well as the means of correcting the direction of steam onto the moving blades.

 In the case of reaction turbines, the pressure drop of steam takes place over the blades. This pressure drop produces a reaction and hence cause the motion of the rotor.

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113. What is the difference between Critical speed & Whirling speed?

In Solid mechanics, in the field of rotor dynamics, the critical speed is the theoretical angular velocity which excites the natural frequency of a rotating object, such as a shaft, propeller or gear. 

As the speed of rotation approaches the objects natural frequency, the object begins to resonate which dramatically increases system vibration. 

The resulting resonance occurs regardless of orientation.

Whirling Speed is due to the unbalanced forces acting on a rotating shaft.

114. What is the significance of Torque(in N-m) given in the engine specification ?

It give the moment about any point or simple rotation.

115. What is the abbreviation of Welding rod 7018?

7018=

70=tensile strength 70000psi 

1= welding position 

8=current flux

116. What are the uses of Graphite electrode in various field.

Graphite electrode is used in EDM.. and in Battery cells..

It is also used in electric arc furnaces to melt the steel .

117. Difference between TIG & MIG welding

Tungsten inert gas welding-non consumable electrode

MIG-Metal inert gas welding-uses consumable electrode

118. What is Specific speed of turbine?

The specific speed is defined as the the speed of the geometric turbine which can produce unit power at unit head

119. Material of Aircraft turbine blade?

Ni, Cr, Al, Traces of C

120. Do you know epicyclic gear box? What are the practical application of epicyclic gear box?

Epicyclic gear box consists of sun gear planetary gears and an annular called ring gear.

Different speed ratios are obtained by locking any one gear.

If you lock any two gear , direct gear will be obtained.

Mostly used in overdrives.

Wrist watch is a practical application of epicyclic gear box

121. What is the function of EGR valve?

EGR means Exhaust Gas Recirculation. 

The main function of EGR is to control NOx emission from the engine. At elevated temperature (during long run & full condition) if due to some reasons engine gets heated up beyond certain level… it produces NOx emission. 

In order to avoid this pollution , we have to control the temperature rise inside the cylinder. 

This can be achieved by mixing some amount of exhaust gas with intake air. By doing this the temperature inside the combustion chamber is reduced. And NOx is controlled.

122. What do you mean by super critical above 500MW in Thermal power plant?

In super critical boiler means all the steam to converted in to superheated steam at outlet of boiler no need to sent to super heater once again.

123. What is the purpose of scrapper ring?

Scrap the excess lube oil from the cylinder walls. There by preventing oil from entering combustion zone.

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124. How catalyst converter works?

In Fuel Cell, a catalyst is a substance that causes or accelerates a chemical reaction without itself being affected. 

Catalysts participate in the reactions, but are neither reactants nor products of the reaction they catalyze.

125. What will happen if relief valve in Hydraulic system fails?

The main function of pressure relief valve is to maintain the pressure in hydraulic system. 

It is one mounting which is used for safety. W

hen pressure increases then safety valve comes into action & if the valve get fail the system get damage due to excessive pressure.

126. What does CC Stand for?

CC is the abbreviated form of cubic centimeter. 

It is the unit by which the capacity of an engine is designated. 

It is the volume between TDC and BDC. 

It represents the quantity of fuel-air mix or exhaust gas that is pumped out in a single piston stroke. 

Alternatively it can represent the volume of the cylinder itself.

We have read that when the piston goes up and down then the engine works i.e. the suction,compression etc etc. then what happens in the case

of big vehicles, which start at stable condition, i.e. how does their piston moves when they are at rest. how suction,compression etc

Smaller vehicles like bikes, cars are started with the help of motors. initially, motors turn the crank shaft till sufficient suction pressure is reached. 

when sufficient suction pressure is reached, the engine starts to suck the fuel in and then the cycle begins when the fuel is taken in and ignited. similarly, for huge engines, instead of motors, we use starting air. air at a pressure of 10-30 bar is fed to the engine which is at rest. this air rotates the engine till it attains sufficient suction pressure. once the pressure is reached, the cycle starts and it starts firing.

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127. What is the difference between S.S to EN8

SS- Stainless steel

En- Medium carbon steel

SS is Non Magnetic material & EN8 is Magnetic material

SS is Corrosion resistant & EN8 is Magnetic material

128. The Compression ratio of Petrol engine is always less than Compression Ratio of Diesel engine why?

Petrol is not self igniting , it needs spark to flame up in chamber. 

Where as diesel is self igniting in dieselengine , to attain that state it requires high temp &pressure. 

This temperature & pressure is more than what’s required in Petrol Engines by property of that fluid.

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129. What is the temperature of space ?

The short answer is that the temperature in space is approximately 2.725 Kelvin.

That means the universe is generally just shy of three degrees above absolute zero – the temperature at which molecules themselves stop moving. 

That’s almost -270 degrees Celsius, or -455 Fahrenheit.

130. How to calculate the speed of conveyer in Meter Per Minute

Measure the diameter of the rollers around which the conveyor belt is wrapped.

Multiply the diameter of the roller by pi (3.14159). 

This calculation will yield the circumference of the rollers. 

Every time the roller spins one revolution, the conveyor will be moved a linear distance equivalent to the circumference of the roller. 

Pi is a dimensionless factor, meaning it does not matter whether inches, centimeters or any other units of measurement are used. 

Measure the revolutions per minute (RPM) of the rollers. Count how many full revolutions (rotations) are made by the roller in one minute. 

Multiply the RPM by the circumference of the roller. 

This calculation will give the linear distance traversed by a point on the conveyor belt in one minute.

131. How can problems of "excessive vibration or noise" due to piping strain be avoided on steam turbines?

 The inlet as well as exhaust steam lines should be firmly supported to avoid strains from being imposed on the turbine.

 Adequate allowance should be made for expansion of steam pipes due to heat.

132. How the deposits in turbine be removed?

 Water soluble deposits may be washed off with condensate or wet steam.

 Water insoluble deposits are removed mechanically after dismantling the turbine.

o Experience shows that water soluble deposits are embedded in layers of water- insoluble deposits. And when the washing process is carried out, water soluble parts of the deposit dissolve away leaving a loose, friable skeleton of water-insoluble deposits which then break loose and wash away.

133. How the fatigue damage on high-pressure blades be corrected?

Fatigue-damage on high-pressure blades arises due to vibration induced by partial- arc admission. 

This can be corrected by switching over to full arc admission technique.

134. How the misalignment of Flanges be rectified?

The bolts holding the flanges together are to be tightened. 

The coupling is to be checked for squareness between the bore and the face. At the same time axial clearance is to be checked.

135. How the problem of excessive speed variation due to throttle assembly friction be overcome?

The throttle should be dismantled. 

Moving parts should be checked for free and smooth movement. 

Using very fine-grained emery paper, the throttle valve seats and valve steam should be polished.

136. How the problems of vibration and fatigue arise in steam turbine blades?

o These arise due to flow irregularities introduced because of manufacturing defects, e.g. lack of control over tolerances.

o System operating parameter,

e.g. low flow may excite various modes of vibration in the blades.

137. How does solid-particle erosion occur?

Solid-particle erosion, i.e. SPE occurs in the high-pressure blades. And it takes place when hard particles of iron exfoliated by steam from super heater tubes, reheater tubes, steam headers and steam leads strike on the surface of turbine blades.

138. How does the internal efficiency monitoring lead to the detection of turbine deposits?

o Process heat drop.

o Adiabatic heat drop.

o The process heat drop and adiabatic heat drop are obtained from a Mollier- Chart for the corresponding values of steam parameters – pressure and temperature – at initial and final conditions.

139. How is a flyball governor used with a hydraulic control?

As the turbine speeds up, the weights are moved outward by centrifugal force, causing linkage to open a pilot valve that admits

and releases oil on either side of a piston or on one side of a spring-loaded piston. The movement of the piston controls the steam valves.

140. What is the difference between rated speed and economic speed?

The rated speed tells us about the maximum speed which can be achieved by a vehicle or some other machine but the economical speed means the speed limit at which the machine works efficiently with least consumption of fuel. 

Example- In normal bikes(not racing),the max.speed limit shown on speedometer is upto 120 kmph but companies always advice their customers to drive such bikes at around 60 kmph to have maximum mileage.

141. What is the purpose of scrapper ring?

scrap the excess lube oil from the cylinder walls.there by preventing oil from entering combustion zone.

142. What are the causes of main engine black smoke?

There is many cause of black smoke. 

1.It is improper mixture of fuel supply by carburetor like very rich mixture so the fuel improper burn.

2. It is when piston or piston ring is fail so back side cooling oil release in combustion chamber it cause black smoke.

3. Improper ignition system like not sufficient time of pressure rise delay period .

143. How cooling tower height selected?

The Function of a cooling tower is to cool the water coming from condenser.

The water coming from condenser is hot and it is sprayed in a cooling tower and a air coming out from bottom cool the water which is coming down.

Outside air is cool and air in inside the cooling tower is hot due to humidity.So there is a density difference between outside and inside air which caused pressure difference.

Pr Difference = g x H x ( density difference) 

Where,

H = Height of chimney

Pr Difference = Pr Difference so that air can flow to cooling tower from outside

144. How does axial thrust balance in multistage pump?

A balancing line from discharge end is connected to suctionside to balance axial thrust.

145. How to calculate the boiler efficiency? Any formula is there?

Boiler efficiency= (heat transferred to feed water in converting it to steam)/(heat released by complete combustion of fuel)

n(eta)= Mass of steam * (h- H(water))/(mass of fuel *calorific value fuel)

What is the significance of torque(in N-

m) given in the engine specification it give the moment about any point or simple rotation.

146. What is the exact requirement of priming?

Priming is done in pumps to remove the entrapped air from the suction pipe thus aiding in smooth operation and avoiding in excess load on the pump.

147. What is the use of a PULLEY?

transmission of power(force) in rotary form

148. Why does cycle rim don’t bend even in heavy loads?

Because of rubber tires. The load is distributed and its effect reduces i.e. tires absorbs heavy load and shocks with the support of steel rim.

The rim has many spokes. The spokes distribute the load equally and the rubber tires absorb more than half of the load.

149. How tonnage can be controlled in PLC base hydraulic press?

Custom integration of press interlocks to inter facing with other parts of the hydraulic press line such as the feeder or transfer systems.

150. What is BHP?

Brake horsepower is the amount of work generated by a motor under ideal conditions. 

This work is calculated without the consideration of effects of any auxiliary component, that may slow down the actual speed of the motor. 

Brake horsepower is measured within the engines output shaft and was originally designed to calculate and compare the output of steam engines.

As per the conventions, 1 BHP equals to:

 745.5 watts

 1.01389 ps

 33,000 ft lbf/min

 42.2 BTU/min

151. What are different between MIG & MAG ?

MIG stands for Metal Inert Gas welding, while MAG stands for Metal Active Gas welding. The main difference lies in the type of shielding gas used.

MIG welding uses inert gases like argon or helium to shield the weld pool from atmospheric contamination, while MAG welding uses active gases like carbon dioxide or a mixture of gases.

MIG welding is typically used for non-ferrous metals like aluminum, while MAG welding is more suitable for ferrous metals like steel.

MIG welding produces cleaner welds with less spatter, while MAG welding can penetrate thicker materials more effectively.

Both processes use a wire electrode that is fed through a welding gun, but the choice of shielding gas determines whether it is MIG or MAG welding.

152. What is PQR Process ?

PQR stands for Procedure Qualification Record.

PQR Process is a procedure used in welding to qualify the welding procedure specification.

It involves testing and documenting the variables used during the welding process.

The purpose is to ensure that the welding procedure will produce the desired quality of welds.

PQR Process is essential for ensuring the integrity and strength of welded joints.

Examples of variables tested include welding parameters, material thickness, and joint design

153. What Is GMAW ?

GMAW stands for Gas Metal Arc Welding, a welding process that uses a continuous solid wire electrode and shielding gas to create a weld.

Uses a continuous solid wire electrode

Requires a shielding gas to protect the weld from atmospheric contamination

Commonly used in industries like automotive, construction, and manufacturing

154. What is WPS Procee ?

WPS Procee is a welding procedure specification that outlines the details of a specific welding process.

WPS Procee includes information such as welding materials, welding parameters, preheat and post-weld heat treatment requirements.

It is essential for ensuring consistency and quality in welding operations.

WPS Procee is often required in industries such as construction, manufacturing, and oil & gas.

Example: A WPS Procee document may specify the type of welding machine to be used, the welding technique, and the required inspection procedures.

155. What is VAR refrigeration system and where it is used? Differentiate VAR & VCR.

Ans. VAR refrigeration system is a type of refrigeration system that uses variable speed compressors to adjust cooling capacity.

VAR stands for Variable Refrigerant Volume or Variable Refrigerant Flow.

It is used in buildings with varying cooling loads, such as hotels, hospitals, and offices.

VAR systems use multiple indoor units connected to a single outdoor unit.

VCR stands for Variable Capacity Refrigeration and uses a variable capacity compressor to adjust cooling capacity.

VCR systems are used in commercial refrigeration applications, such as supermarkets and cold storage warehouses.

156. What is all boiler parameters values for startup and runing condition?

Boiler parameters values vary depending on the type of boiler and fuel used.

• Boiler pressure
• Boiler water level
• Fuel flow rate
• Air flow rate
• Steam temperature
• Steam pressure
• Feedwater temperature
• Blowdown rate

157. How to calculate bearing number to diameter of the inner and outer

Divide the shaft diameter size by 5, it will give last two digit of the bearing no. and according to type of load we have to chose the type of bearing and that will give prior no. of the bearing.

158.Definition of Octane number & Cetane number

Octane No.- 

Octane number is defined as the percentage, by volume, of iso octane in the mixture of iso octane and h-heptane. It is the measure of rating of SI engine.

Cetane No.- 

Cetane number is defined as the percentage, by volume, of n-cetane in the mixture of n-cetane and alpha methyl naphthalene. It is the measure of rating of CI engine.

159. What is the other name of Micro meter & Vernier Caliper?

Micrometer’s other name is Screw Gauze.

Vernier caliper’s other name is slide caliper.

160. Define failure rate?

Failure rate is the ratio of the number of failures during particular unit interval to the average population during that interval. This failure rate is also known as hazard rate and instantaneous failure rate.

161. What is Mean Failure Rate?

The mean failure rate h is obtained by finding the mean of the failures rates for specified period of time.

where Zt represents failure rates over the specified period of time T.

162. Define Mean Time to Failure.

Let t1 is the time to failure for the first specimen, t2 is the time to failure for the second specimen and t n is the time to failure for the Nth specimen. Hence the mean time to failure for N specimens are

MTTR = (t1+t2+......+t N) /N

163. What is Mean Time between Failures (MTBF)?

Mean Time between Failures (MTBF) is the mean or average time between successive failures of a product. Mean time between failures refers tom the average time of breakdown until the device is beyond repair.

164. Define Mean Time to Repair (MTTR)?

Mean Time to Repair is the arithmetic mean of the time required to perform maintenance action. MTTR is defined as the Ratio of total maintenance time and number of maintenance action.

MTTR = Total maintenance time/ Number of maintenance action.

165. Define Maintenance Action Rate?

Maintenance action rate is the number of maintenance action that can be carried out on equipment per hour.

166. Define Failure Density?

Failure Density is the ratio of the number of failures during a given unit interval of time to the total number of items at the very beginning of the test.

167. State the types of reliability?

Reliability can be generally of two types:

(i) Inherent Reliability: It is associated with the quality of the material and design of machine parts.

(ii) Achievable Reliability: It depends upon other factors such as maintenance and operation of the equipment.

168. Draw the equipment life cycle and name the various phases ln it?

Phase I - Failure pattern inherent in a new product because of manufacturing or design defects.

Phase II - Life period of an equipment

Phase III - Failures due to wear out conditions because to aging of the equipment.

169. Define maintainability?

Maintainability is defined as the probability that a unit or system will be restored to specified working conditions within a given period when maintenance action is taken in accordance with the prescribed procedures and resources. 

170. Define availability?

Availability is the ratio of the time at which equipment is available for the designated operation/service to the total time of operation and maintenance of the equipment. It is also defined as the ratio of equipment uptime to the equipment uptime and downtime over a specified period of time.

171. State the advantages of life cycle cost analysis.

(i) Integration of engineering, economics and financial aspects lead to the way of robust metric for the selection and purchase equipment required for the industry.

(ii) Reduced operating and maintenance cost of equipment due to cost analysis over span of time.

(iii) It leads to the selection of proper and economically viable equipment.

172. Draw the curve to determine the economic life of equipment?

The economic life of equipment depends on the maintenance and repair costs, availability and operational efficiency. A plot of cumulative efficiency and maintenance and repair cost per cumulative hours Vs operating hours of the equipment to find the economic life of the equipment is shown in the figure.

173. State the components of maintenance cost?

The maintenance cost is comprised of two factors:

(i) Fixed cost: This includes the cost of support facilities including the maintenance staff.

(ii) Variable cost: This includes the consumption of spare parts, replacement of components and cost other facilities requirements of maintenance.

174. State the role of maintenance budget

The maintenance budget is used to set aside certain amount of money to meet the expenditures incurred in achieving the objectives of maintenance.

175. State the types of maintenance budget?

(i) Appropriation Budget : Budget used to allocate money for each activity independently.

(ii) Fixed Budget: Fixed used to allocate money for a specified period of time.

(iii) Variable Budget: Dynamic allocation of expenditure based on maintenance requirements and activities.

176. List the main factors of maintenance cost?

The maintenance cost is comprised of two factors:

(i) Fixed cost: This includes the cost of support facilities including the maintenance staff.

(ii) Variable cost : This includes the consumption of spare parts, replacement of components and cost other facilities requirements of maintenance.

Preventive Maintenance

177. Define the term Preventive Maintenance?

It is a maintenance program which is committed to the elimination or prevention of corrective and breakdown maintenance. It is designed for day to day maintenance like cleaning, inspection, lubricating, retightening etc. to retain the healthy condition of equipments.

178. Define predictive maintenance?

Predictive maintenance is a management technique that uses regular evaluation of the actual operating conditions of plant equipment, production systems and plant management function to optimize total plant operation.

179. What is meant by Breakdown maintenance approach?

It is a type of maintenance approach in which equipment is allowed to function / operate till no failure occurs that no maintenance work is carried out ion advance to prevent failure.

180. Classify various planned maintenance approach.

1. Preventive maintenance

2. Corrective maintenance

3. Predictive maintenance

4. Condition based maintenance

181. Define corrective maintenance approach.

Corrective maintenance is the program focused on regular planed tasks that will maintain all critical machinery and system in optimum operation conditions

182. What is meant by preventive maintenance approach?

A comprehensive preventive maintenance program involves periodical evaluation of critical equipment, machinery to detect problem and schedule maintenance task to avoid degradation in operating conditions. It is designed for day to day maintenance like cleaning inspection, lubricating, retightening etc. to retain the healthy condition of equipments.

183. List the objectives of corrective maintenance?

1. Elimination break downs

2. Elimination deviations from optimum operating condition.

3. Elimination unnecessary repairs

184. What is meant by predictive Maintenance?

Predictive maintenance is a management technique that uses regular evaluation of the actual operating conditions of plant equipment production systems and plant management functions to optimize total plant operation.

185. List out some condition based monitoring techniques and briefly discuss on them.

1. Vibration monitoring

2. Thermograph

3. Tribology

4. Electrical motor analysis

186. What is meant by Reliability Centered Maintenance (RCM)?

Reliability centered maintenance is one of the well-established systematic and a step by step instructional tool for selecting applicable and appropriate maintenance operation types. It helps in how to analyze all failure modes in a system and define how to prevent or find those failures early.

187. What is Total Productive Maintenance (TPM) and discuss its similarities with TQM?

Total productive maintenance is a maintenance program which involves a newly defined concept of maintaining plants and equipments. 

The goal of TPM program is to significantly increase the production, at the same time increasing employee morale and job satisfaction.

188. What does safety, health and environment pillar of TPM aims at?

This pillar aims at achieving Zero accident, Zero health damage and Zero fires.

189. What is limitation of breakdown maintenance?

1. Most repairs are poorly planned due to time constraint caused by production and plant management.1 This will cost three to four times than the same repair when it is well planned.

2. This approach focus only on repair or the symptoms of failure and not on the root cause of failure. This results only in increase in the frequency of repair and correspondingly the maintenance costs.

190. List the benefits of implementing preventive maintenance.

1. It maintains the equipment in good condition to prevent them from bigger problems.

2. Prolongs the effective life of the equipments.

3. Detects the problem at earlier stages.

4. minimizes/eliminates the rework/scrap and helps in reducing the process variability

5. Significantly reduces unplanned downtime.

191. List the various pillars of TPM?

1. 5,S Principle

2. Jishu Hozen (JH)

3. Kaizen

4. planned maintenance

5. Quality maintenance.

6. Training

7. Office TPM

8. Safety, Health and Environment

192. What are the objectives of TPM?

The main objectives of TPM are

1. To achieve zero defects

2. Achieve zero accidents and zero break downs in all functional areas of an organization

3. To create different team of people to have active participation.

4. To aim at minimization of defects and

5. To inculcate autonomous policy.

193. Name the various stakeholders of maintenance scheduling.

1. Operators

2. Planners

3. Schedulers

4. Maintenance supervisors

5. Craftsman

6. Store’s in charge

7. Operation superintendent

194. Define Maintenance Scheduling.

Maintenance scheduling is a joint maintenance operations activity in which maintenance agrees to make the recourses available at a specific time when the unit can also be made available by operations.

Condition Monitoring

195. What is equipment health monitoring?

Conditions monitoring is one of the maintenance methods which are used to assess the health and condition of equipments machines, systems or process by absorbing checking, measuring and monitoring several parameters. This technique is also called as equipment health monitoring.

196. List down the factors for increasing the demand condition monitoring

1. Increased quality expectations reflected in produces liability legislation

2. Increased automation to improve profitability and maintain competitiveness

3. Increased safety and reliability expectations

4. Increased cost of maintenance due to labour and material cost.

197. List down the key features of condition monitoring.

1. Links between cause and effect

2. Systems with sufficient response

3. Mechanisms for objective data assessment

4. Benefits outweighing cost

5. Data storage and review facilities.

198. Write down the basic steps in condition monitoring.

1. Identifying critical systems

2. Selecting suitable techniques for condition monitoring

3. Setting baselines

4. Data collection

5. Data assessment

6. Fault diagnosis and repair

7. System review

199. What are three types of condition monitoring?

a. Subjective condition monitoring

b. Minimized breakdown costs

c. Improved morality of the operating personnel and safety.

200. State the advantages and disadvantages and disadvantages of condition monitoring.

Advantages

1. Improved availability of equipment 

2. Minimized breakdown cost

3. Improved reliability

Disadvantages

1. Gives only marginal benefits

2. Increased running cost

3. Sometimes difficult to organize

201. Mention the various costs involved in costing of condition monitoring mainly

I. Installation cost

II. Operating cost

202. State the methods of measuring vibration

a. Amplitude

b. Frequency

c. Phase

203. Name the types of pyrometers.

1. Total radiation pyrometers

2. Infra red pyrometers

3. Optical radiation pyrometers

204. Mention the application of bimetallic strip.

1. Bimetallic strips are frequently used in simple ON – OFF switches.

2. The bimetal strips are also used in control switches.

205. List down the features of RTD.

1. High degree of accuracy

2. Resistance thermometer is interchangeable in a process without compensation or recalibration.

206. State the application and limitation of Thermisters.

Applications:

1. It is used for varying temperatures

2. it is used in time delay circuits

3. Thermistors are used for temperature compensation.

207. What are two main types of infrared Themography?

1. Passive thermography

2. Active thermography

208. What are the principles very important for the study of eddy current test.

i. Permeability

ii. Conductivity

iii. Material thickness

iv. Edge effect and end effect

v. Lift off

vi. Fill factor

209. Describe the limitation of eddy current test.

The main limitation is the low penetration of parts being examined, using limited to thin walls or near surface flaws. It is difficult to use on ferromagnetic materials.

False indications are possible because of mixed variables, edge effects and lift-off effects. Extensive technical knowledge is required for the development of inspection procedures, specific probes and to interpret the inspection data.

210. Mention th effect of X-rays to human body?

I. Injuries to superficial tissue

II. General effects on the body, particularly the blood forming organs; eg. Producers of anema and leukerma

III. Induction of mahgnant tumors.

IV. Genetic effects.

211. What are the limitations of Ultrasonic test?

a. Unfavorable geometries and coarse anisotropic grain structures are difficult to inspect.

b. extensive technical knowledge is required for the development of inspection procedure.

c. Parts that are rough, irregular in shape, very small or thin or not homogenous are difficult to examine, specific probes and to interpret the inspection data.

212. Name some of the methods of leakage monitoring.

1. Interstitial monitoring

2. level monitoring

3. Vapor monitoring

4. Liquid Monitoring

213. Define see back effect?

The basic principle of thermocouple is ‘when two dissimilar metals are joined together and emf will exist between the two points A and B, which is primarily a function of the junction temperature. The above said to be principle of see back effect.

214. State the various methods of corrosion monitoring?

a. Weight loss method

b. Electrical resistance method

c. linear polarization method

d. corrosion potential measurement

e. Ultrasonic testing

f. Sentinel hole method.

Repair Methods for Basic Machine Element

215. Define the term failure.

The term failure may be defined as

1. Any loss that interrupts the continuity of production

2. A loss of assets availability

3. The unavailability of equipment

4. A deviation from the status quo

5. Not meeting target expectations

6. Any secondary defect.

216. What are the various possible causes for a failure ?

•  Unexpected and unintentional damage 
•  Workmanship
•  Improper design
•  Manufacturing defects
•  Incorrect usage of equipment

217. Define failure analysis?

Failure analysis is the process by which information/data about failure occurring in equipments/ systems are collected and analyzed to find the root cause of failures, and the causes are addressed to prevent recurrence of failures.

218. Name the three types of failure models?

• Predictable failure model
• Unpredictable failure model
• Running-In-Failure model

219. What are called age-dependent failures?

Time dependent failures are called age dependent failures

220. What are predictable failures?

In spite of all the working conditions maintained at same level, the cause of failure will be random in nature and cannot be assigned to any particular mechanism of failure. This type of failures is called Unpredictable Failures.

221. What are Running In Failures?

Suppose if some components/ equipments are installed with unnoticed defects, may fail in a short duration after installation than during its useful life. This type of failures is Running In Failures.

222. Define Fault tree diagrams

Fault tree diagrams are logic block diagrams that display the state of a system in terms of the states of its components.

223. Write down the capabilities of Fault Tree Diagram.

1. Fault tree analysis and failure modes and effects analysis,

2. Design for reliability

3. Design for safety

224. Define Event tree Analysis

An event tree is a visual representation of all the events which can occur in a system. As the number of events increases, the pictures fans out like the branches of a tree

225. What is the aim of event tree analysis?

The aim of event tree is to determine the probability of an event based on the outcomes of each event in the chronological sequence of events leading up to it. By analyzing all possible outcomes, we can determine the percentage of outcomes which lead to the desired result.

226. Define Root cause analysis?

RCA is a step by step method that leads to the discovery of faults first or root cause. Every equipment failure happens for a number of reasons. There is a definite progression of actions and consequences that lead to a failure. An RCA investigation from the end failure is back to the root cause.

227. Define FMEA?

FMEA is methodology for analyzing potential reliability problems early in the development cycle where it is easier to take actions to overcome the issues, thereby enhancing reliability through design.

228. Define Risk Priority Number(RPN)

Risk priority numbers is the product of the numerical severity, occurrence and detection ratings.

RPN = (S) X (O)X(D)

229. Name the factors based on the satisfactory performance of gears/drives.

I. Proper design and manufacture of drive

II. Selection of proper type and size

III. Proper installation

IV. Proper use of service

V. Proper maintenance of unit in it entire life.

230. Name the factors that contribute to tooth breakage.

The common reasons for gear tooth breakage may be due to any of the following reasons

a. Fatigue

b. Heavy wear

c. Overload

d. Cracking

231. List some of the inspection performed on gears

1. Pitch error

2. Axial and

3. Radial run out

4. Tooth profile

232. Name some of the geometric properties that are checked for guide ways.

1. Straightness

2. Flatness

3. Parallel both on horizontal and vertical surfaces.

232. What are the factors influence the performance of sleeve bearings.

The following are the factors that affect the bearing performance:

1. Dirt

2. Fatigue

3. Hot Shot phenomenon and

4. Crush problem

234. Define Crush

Normally, the bearings are manufactured so that they are slightly longer circumferentially than the mating housing. The bearing will be elastically deformed during assembly. If the amount of crush is insufficient, relative motion occurs between the bearing and its bore, which causes fretting and makes the bearing back a highly polished or pitted.

Repair Methods for Material Handling Equipment

235. State few examples of material handling equipments.

Material handling equipments include carts, hand trucks, fork lifts, conveyors, shelf pickers and other specialized industrial trucks powered by electric motors or internal combustion engines.

236. State the benefits of proper maintenance of material handling equipments.

The benefits of a maintenance program for material handling equipments are to maintain the high efficiency, keep them in running condition, reduce the cost of repairs, safer operation and enhanced productivity.

237. State the major stages in preventive maintenance of material handling equipments.

There are three stages of preventive maintenance are:

1. Inspection

2. Repair and

3. Over haul

238. State the various phases present in a good maintenance management system.

1. Work identification

2. Planning

3. Scheduling

4. Execution

5. Recording and

6. Analysis

239. Define the term Computerized Maintenance Management System (CMMS)

Computerized maintenance management system is the application of computers in planning, scheduling, monitoring and control of maintenance activities.

240. State the objectives of CMMS.

1. Maintenance of existing equipments

2. Inspection and service of the equipment

3. Installation or revamping of the equipment

4. Maintenance storekeeping

5. Craft administration

241. State the advantages of CMMS.

1. Improve maintenance efficiency

2. Reduce maintenance costs

3. Reduce the equipment downtime by proper scheduling preventative maintenance.

4. Provide maintenance reports in specific formats depending on the requirements.

5. Quicker access to plant maintenance statistics

242. Define work order system.

Work order system is the information system used by the industry to keep track of its maintenance works.

243. Mention the use of work order backlog.

Work order back log is used to find out all active maintenance works order in an industry.

244. What is job card?

Job cards contain necessary details for performing individual job in maintenance organizations. Job card may be in the form of a card, sheet or printout.

245. State the benefits of job card system.

1. Information about maintenance history

2. Knowledge of frequency of frequency of maintenance for equipments

3. Details of equipments which require maximum resources

4. Helps in job auditing

5. Evaluation of cost of maintenance.

246. State the role equipment records in maintenance.

Equipment records are information containing the details of installation, service, repair, maintenance activities, schedules and plans for future implementation. Equipment records are to be used to maintain control on maintenance cost, reliability and availability.

247. State the benefits of keeping equipments records.

1. Clear picture about the details of maintenance programmes is obtained.

2. Information about completed, pending and regular jobs carried out to the equipment are available

3. Records disseminated to various units of the industry.

4. Helps in standardization of procedures.

5. Evaluation of performance of maintenance tasks.

248. List some of the inspection performed on gears

• Pitch error
• Axial and
• Radial run out
• Tooth profile

249. List the main factors of maintenance cost?

The maintenance cost is comprised of two factors:

(i) Fixed cost: This includes the cost of support facilities including the maintenance staff.

(ii) Variable cost : This includes the consumption of spare parts, replacement of components and cost other facilities requirements of maintenance.

250. Name the three types of failure models?

• Predictable failure model
• Unpredictable failure model
• Running-In-Failure model

251. What are two main types of infrared themography?

1. Passive thermography

2. Active thermography

Principles and Practices of Maintenance Planning

252. What are the principles of maintenance?

a) Plant management in maintenance work:

The main role of a maintenance function is to provide safe and effective operation of the equipment to achieve the desired targets on time with economics usage of resources.

b) Production and maintenance objectives:

The plant operation is driven by the production targets. The objective of maintenance function is to support these target. The achievement of desired goals of Athe production system is to be supported by both the production and maintenance department to ensure smooth and successful operation of the industry.

c) Establishment of work order and recording system:

The maintenance system should have proper work and recording system. The work order for the maintenance function indicates the nature of work to be performed and the series of operations to be followed to execute a particular job. It is necessary to maintain proper records and entries to monitor the maintenance function.

d) Information based decision making:

The maintenance objectives are successfully achieved by the use of reliable information system. This information is used to meet the manpower and spare parts re4quirements of the industry.

e) Adherence to planned maintenance strategy:

A sound maintenance management should adhere to the planned maintenance strategy. This also includes the use of manufacturer information on the life and maintenance schedules of the equipment and other material resources available.

f) Planning of maintenance function:

All the maintenance function are to be carefully executed by a way of proper planning to ensure the effective utilization of manpower and materials.

g) Manpower for maintenance:

The manpower requirement of the maintenance system must be carefully evaluated based on the time and motion study. The requirements should also satisfies the need arising in case of overhauls, component replacement, emergency and unscheduled repair.

h) Work force control:

Determination of exact work force required to meet the maintenance objectives of the system is difficulty task due to the element of uncertainty. Hence the proper control and monitoring of workforce are needs to be ensured.

i) Role of spare parts :

A good maintenance management system requires appropriate tools. So the system should have good quality tools and that too available in required quantities to ensure the proper function of the maintenance work.

j) Training of maintenance work force:

Training of the workforce must be integral part of any good maintenance management system. Training helps the workforce to learn about the modern techniques, recent trends in maintenance and to chalk out a strategy to meet the growing demands of the industry.

253. What are important factors considered in maintenance planning?

a) Job distribution:

The first and foremost task in maintenance planning is the distribution of the jobs to the personnel for preventive and emergency maintenance works. It is the practice to form two separate task groups to tackle the both. If not possible a same group can also be used to tackle both the situations in such way that during scheduling, time must be devoted for unforeseen breakdowns or situations in maintenance.

b) Program :

The development of maintenance programs involves o Selection of activities for maintenance

•  Determination of the frequency of preventive maintenance
•  Decision on the cost effective methodology

Selection of activities

This selection is based on cost involved between preventive and breakdown maintenance.

c) Manpower allocation:

The manpower allocation is the most important task of the maintenance management group. It provides adequate manpower to execute various jobs in the system. This should also take into consideration the skill level of personal deputed for the maintenance tasks. The central idea of manpower allocation can be drafted using the information available from maintenance records and planning the task to meet the objectives of the organization.

d) Staffing:

Staffing is the task of providing the required manpower for the maintenance function. This has to be achieved at optimum cost. Staffing is depend upon the ability of the organization to tackle the regular as well as attending the unforeseen situations.

Staffing should be sufficient to handle preventive and emergency maintenance task.

e) Planning technique :

The planning methods are Gantt charts, Milestone method, Critical path method and program evaluation review. Evolutionary computation based techniques are recently used for maintenance planning and scheduling.

f) Planning procedure:

Planning procedure involves four step processes. Organizing maintenance resources to ensure their effective use in future

· Scheduling the resources for the planned period

· Execution of plans according to the schedules

· Establishing a feedback system for all the above processes to know the deficiencies of each of the processes.

g) Estimation of maintenance work:

Estimation is used to find out the quantity and quality of the maintenance work. This will help in allocation of the required manpower. The following methods are used for the estimation of maintenance wok. Measurement by estimates, historical data and by conventional standard time data.

h) Maintenance control:

Maintenance control is the auditing techniques to ensure the effective utilization of the maintenance budget. This involves the integration of accountability with in the system. Proper accounting of maintenance work should be carried out at every level of the maintenance organization.

255. What is the difference between preventive and predictive maintenance?

Preventive maintenance is performed at regular intervals to avoid breakdown, 

While predictive maintenance uses data and condition monitoring to anticipate failure before they occur.

256. Explain how you would set up and manage a maintenance schedule for equipment.

I would identify critical equipment review manufacture recommendations and use a CMMS to create calendar for routine inspection, lubrication, and parts replacement.

257. Can you describe your process for troubleshooting a malfunction machine?

I start by identifying symptoms, consulting schematics or manuals testing components and isolating the issue step by step before applying the necessary fix.

258. How do you prioritize maintenance tasks during a busy shift?

A: I assess the impact on safety, production and cost addressing critical equipment or safety hazards first.

259: How do you identify and fix issues in a hydraulic system?

I check for leaks, inspect hoses and seals, measure pressure levels, and clean or replace filter to ensure proper operation.

260. Can you explain the steps to replace a motor or pump?

I would isolate power, remove the defective unit, align the the new motor or pump, secure it, reconnect wiring or piping, and test for proper function.

261. What are the common signs of mechanical wear and how do you address them?

Signs include unusual noises, vibration, or visible wear on components. I address them by replacing worn parts and ensuring proper lubrications.

262. How do you ensure alignment of shafts, belts, or coupling?

I use alignment tools, such as laser alignment system or dial indicators, to adjust until tolerance are within speciation.

263. What is your experience with pneumatic system and their components?

I worked with air compressor, regulator, valves, and actuators, ensuring proper air pressure and system integrity.

264. What are major parts of the centrifugal pump?

Rotary parts: Shaft, Impeller, Coupling, Mechanical seal, Oil rings

Stationary parts: Casing, Stuffing box, Bearing housing

265. Explain overhauling steps for a back pullout pump?

Example Pump made: PACIFIC made: HVC

1. Remove coupling guards after getting clearance of safety aspects like electrical isolation, process lines drainage etc.

2. Remove coupling spacer and loose the casing bolts connects the stuffing box frame after removing and draining oil level glass and lube oil from bearing housing.

3. Pullouts back the pump from casing with care of casing gasket.

4. Dismantle all parts from the pump unit as impeller, mechanical seal assembly, shaft sleeve, coupling, and bearings respectively with high care.

5. The following factors should be checked and recorded for future to estimate the performance condition of the pump, are wear ring clearance, seal compression, shaft deflection, thrust, trueness etc while or after dismantle.

6. Proper tracing of parts need to any vision able damage like crack, score, break etc.

7. Best is changing new one comparing reconditioning of parts.

8. Assembly is the reversing procedure of dismantle as before seen.

9. Before coupled alignment should be checked and corrected

266. What is impeller back clearance?

The clearance between the backside of the impeller (shroud) and the stuffing box or crown (wear) plate.

Actually this clearance standardize the stuffing box pressure and should be strictly followed incase of depressurizing vanes on impeller and semi open impellers.

267. How do you check impeller back clearance?

By the use of feeler gauge and with dial indicator as possible.

268. How do you adjust impeller back clearance?

a. Add or remove shims behind the stuffing box.

b. Changing the position of the rotor depends clearance if possible.

c. Machining of impeller hub if there is no another way

269. What is impeller front clearance?

The clearance between the front side of the impeller (crown) and the casing or wear plate

This clearance should be strictly followed incase of semi open impellers

270. How do you check impeller front clearance?

By the use of feeler gauge and with dial indicator as possible

271. How do you adjust impeller front clearance?

Add or remove casing gasket thickness

272. What is fixed bearing?

The bearing fixed with out any allowable axial clearance to permit thermal expansion.

This bearings bears the thrust load and only has thrust allowance of 0.001 – 0.003 inches

273. Where is fixed bearing located?

a. In back pullout pumps, fans – inboard

b. Double suction single discharge pump – outboard

c. Mixers (agitators) – top bearing

274. What is floating bearing?

The bearing fixed with allowable clearance to permit thermal expansion. And takes radial load normally.

275. Where is floating bearing located?

a. In back pullout pumps, fans – outboard

b. Double suction single discharge pump – inboard

c. Mixers (agitators) – bottom bearing

276. What is necessity of floating bearing?

1. Elongation due to thermal expansion of shaft

2. Axial fluctuation effects by load

277. What is bearing back-to-back arrangement?

278. Why bearing back-to-back arrangement is provided?

The back-to-back arrangement can support combined axial and radial loads and will keep the pump shaft end movement within acceptable limits. 

A bearing pair will support an axial load equally in either axial direction. It should preferably have a slight clearance (0 to 0.002 inches) with the bearing housing end cover.

279. In which series bearing back-to-back arrangement is available?

1. Single row angular contact ball bearing

2. Taper roller bearing.

280. How do you check plain journal bearing clearance?

i. By taking measurement difference between shaft outer and bearing inner diameters.

ii. By the use of plastic gauge or lead wire.

281. Is there any thumb rule for journal bearing clearance?

Bearing clearance necessary depends upon oil viscosity, speed and load. 0.001per 1 inch of journal diameter plus 0.0015 inches up to 9000 feet per minute journal velocity.

Above this speed 0.002 inches per 1 inch of journal diameter for shaft larger than 2.5 inches.

282. Have you seen tilting pad journal bearing?

Yes.

283. What is the advantage of tilting pad journal bearing over plain journal bearing?

Suitable for higher speeds and loads and has greater stability. It avoids the possibility of oil whirl and allows self-aligning.

284. How do you adjust tilting pad journal bearing clearance?

By add or remove shims behind the shoes of tilting pads.

285. How do you polish journal bearing?

With the use of special polish oil (brasso) and 4/0 fine emery sheet or sponge pad. A special tool

named as bearing scrapper used to clear deep able scratches.

286. What is spherical seated journal bearing?

The spherical seated journal bearing in which the shell of bearing in the form of spherical by which it allows self-accommodation on housing depends shaft aligns.

287. What are the various ways to check tilting pad journal bearing clearance?

a. By keeping dial indicator on shaft vertically besides bearing and lift the shaft to find out clearance of bearing through indicator reading.

b. By the use of mandrel as same diameter of shaft and moving bearing.

c. By manual measurement = diameter of pivot – (2 x thickness of individual pad) – diameter of the shaft.

288. Give the ‘go’, ‘no go’ gauge dimensions for a 100 mm journal diameter with a minimum bearing clearance of 0.16 mm and maximum bearing clearance of 0.25 mm?

Go gauge dimension - 100.16 mm

No go gauge dimension- 100.26 mm.

289. Why plastic gauge are preferred rather than lead wire?

a. Lead wire expands after removal from cap

b. It can be become embedded in the Babbitt; especially in soft, high lead Babbitt bearing.

c. Plastic gauge doesn’t need skill more and it is easy to identify just comparing the compressed

width of plastic with the gauge paper.

290. Why spherical seated bearings are used?

 To allow self-accommodation on housing depends shaft aligns.

291. What is bearing crush?

Actually it defines the compression fit

of the split type journal bearings

diametrically and will not exceed more

than maximum of 0.003 inches.

292. How do you check bearing crush?

Keeping 0.004 to 0.010 inches of shim according the plastic gauge series on the face of half split

bearing housing and measuring the clearance between the bearing shell and cap (top cover) of bearing housing with the use of plastic gauge after tightening cover.

Now the bearing crush = shim thickness – plastic gauge reading.

293. How do you adjust bearing crush?

By providing shim piece in-between bearing shell and top cover of the bearing housing.

294. How do you check thrust-bearing clearance?

Keep the dial indicator horizontally on rotor in any accessible point. Move the rotor shaft

longitudinally to find out the thrust clearance of the bearing after fixation of radial and thrust bearings.

295. How do you adjust thrust-bearing clearance?

Add or remove shims on the thrust-bearing collar if provision given otherwise

Machining carried on in case of no other way.

296. How do you identify bearing pads based on their pivot?

Left hand and right hand pads.

297. How do you identify RH & LH pivoted pads?

If the loading point of pad on the right side called RH pads when seeing in front of the pad face. If the loading point of pad on the left side called LH pads when seeing in front of the pad face.

298. If the DOR of a rotor CW looking from C/E, where will you locate RH & LH pads?

Right hand pads on opposite side of coupling end.

Left hand pads on the coupling side.

299. What is adaptor sleeve & withdrawal sleeve?

These sleeves used to fix and remove bearings easily on that and to be fixed any accessible place on the rotor. 

In adaptor sleeve, bearing is fastened while the adaptor sleeve nut tightened. In withdrawal

sleeve nut is used to withdraw bearing from its position from the withdrawal sleeve.

300. How do you specify a bearing lock nut & lock washer?

N - for bearing locknut

W - for bearing lock washer

301. What is rotor free float?

It defines the total axial movement of rotor without thrust bearing.

302. Explain rotor centering?

It is the process of keeping rotor half of the free-float through the position of thrust bearing in the

bearing housing fixation.

303. How do you adjust rotor centering without affecting axial float?

Increase or reduce the thickness of centering spacer fixed behind the thrust bearing on shaft.

Add or remove gasket on the end covers of bearing housing. It allows only slight adjustment otherwise machining carried out on end cover in case of no other way.

304. What is radial centering?

Aligning the rotor axis in the same line with centerline of casing confined recess provided for the fixation of wear ring, neck bush, etc. radially. This centering keeps and helps to maintain constant gap between wear ring, neck bush, etc.

305. How do you adjust radial centering?

By the use of adjusting screws provided on the bearing housing carrier.

306. Explain the overhauling sequence for a multi stage centrifugal pump?

Example Pump made: PACIFIC model: R X 1J. 9

1. Remove coupling, hub with the use of puller

2. Remove bearing housing top covers of both in board and out board sides

3. Take out journal and thrust bearing in the out board side and journal bearing in the inboard side

4. Dismantle bottom bearing split housing of outboard side.

5. Remove thrust collar from shaft.

6. Remove all seal parts from head on both sides

7. Cover the shaft on the bearing seated surface finished area by tape

8. Loosen and remove the head bolts connected with barrel of pump to let the rotor free to remove after taking out the head from position by the jack bolts provided on the head. Care should be taken about the gaskets, inner and outer and the removal of discharge diffuser case.

9. Fix the fixture to guide the rotor assembly

10. Pullout the rotor assembly including inlet guide vane case, intermediate stage housings with care.

11. Check the key way of barrel

12. Transfer the rotor assembly to workshop for the next step of action

13. Remove tie rods, which connects of all cases and key on the cases.

14. Remove balancing piston by loosening locknut.

15. Dismantle diffuser, stage bush, impeller, impeller keys, inlet guide vanes with diffuser of all stages respectively.

16. Now the dismantling of all parts completed.

17. Proper tracing of parts need to any vision able damage like crack, score, break etc while

dismantling

18. The following measurements should be measured and recorded for analyzing the performance like, wear ring clearances, stage bush clearances of all stages, bearing diametric clearance, thrust allowance, shaft trueness, seal setting compression etc while and after dismantling.

19. Care should be taken about all allowable factors with in design limit

20. Changing new parts is better than re conditioning

21. Assembling is the reversible procedure of dismantling before seen. Proper tightening torque should be followed is carry over.

22. Before coupled with drive alignment should be checked and corrected to retain with in limit.

306. What do you mean by wear rings?

Wear rings are removable rings fixed on either impeller eye and casing or both of them.

307. What is the purpose of wear rings?

To avoid the change of impeller and casing due to pitting corrosion.

To minimize the flow of liquid from high pressure of discharge to low pressure of suction eye

308. What are the different types of wear rings?

1.Serrated wear rings, 

2. Stepped wear rings, 

3. Reverse thread wear rings, 

4.thrust balancing wear rings, 

5. Flat wear ring, 

6. L shaped wear ring, 

7. Impeller wear ring, 

8.casing wear ring, 

9.double ring with labyrinth leakage joint wear ring.

309. How do you check wear ring clearance?

Means of measuring the outer diameter of impeller wear ring or impeller eye and the inner diameter of the casing wear ring inner diameter by the use of micrometer or vernier caliper and with the use of feeler gauge if possible.

310. How do you adjust wear ring clearance?

By machining wear rings or change as new one if the clearance more.

311. How do you fix eyewear ring & casing wear ring?

Interference fit with Allen screw lock, pin with spot weld, direct bead weld, threading etc.

312.What the different types of shaft sleeve?

Threaded sleeve, sleeve with locknut, sleeve with Allen lock, straight sleeve, stepped sleeve, throttle sleeve, throat sleeve, etc.

313. Where are throttle sleeve & throat sleeve located in a rotor?

Throat sleeves located on throat bush area to control the flow of pumping liquid in to stuffing box area.

Throttle sleeves are used in slurry service to avoid the flow of slurry liquid into seal area with the use of throttle packing which allows only the flushing liquid into pumping liquid area instead of reversing that’s why flushing fluid pressure is kept 15 psi more than suction pressure. ENSIVAL pump design has the provision of both throttle and throat bush arrangement.

314. Draw a balanced opposed rotor arrangement?

315. Why balanced opposed rotor arrangement is preferred?

This arrangement minimizes axial thrust load of rotor by keeping the low pressures (suction pressure) on both side by the arrangement of impellers.

To attain the critical speed of the equipment apart from the working speed

316. Where is balance drum located in a rotor?

d- discharge pressure side; 

s- suction pressure side

The balancing drum is located, behind the last stage of impeller.

317. What is the purpose of balance drum?

Used to take 90% of thrust load by liquid and the residual thrust is supported by the thrust bearing.

318. What is the applicable API standard for centrifugal pumps?

API 610.

319. What do you mean by oil wedge?

Under normal operating condition, the shaft of the machine  will rise slightly up the side of the bearing. The amount of  rise depends on shaft RPM, rotor weight and oil pressure. 

The shaft, thus operating in an eccentric position relative to the bearing center, draws oil to produce a pressurized load- carrying film called as ‘oil wedge’.

320. What do you mean by oil whirl and oil whip?

The eccentricity of oil wedge is momentarily increased from its equilibrium position, perhaps due to a sudden surge, an external shock load or other transient condition, additional oil is immediately pumped into the space vacated by the shaft. 

The result is an increase in the pressure of the load- carrying film. 

The additional force developed by the oil-film can drive the shaft into a whirling path

around the bearing. 

If the damping within this system is sufficiently high, the shaft returns to its normal position in the bearing; otherwise the shaft continues in a whirling path called ‘oil whirl’

Lack of lubrication or improper lubrication causes excessive friction between the stationary bearing and rotating shaft, and the friction excites vibration in the bearing and other related parts similar wiping a moisture finger over a dry plane of glass called ‘oil whip’.

321. What is hydrostatic lubrication?

The pressurized lubrication oil given on oil wedge for lubricating and creating oil film in-between the moving parts. This type of lubrication called hydrostatic lubrication.

322. What is hydrodynamic lubrication?

The moving parts make the lubricating film in between contact area while running itself. This type of lubrication named as hydrodynamic lubrication.

323. What is forced feed lubrication?

Actually it is a pressurized lubrication, oil wedge formed by the pressure induced from separate lube oil pump, which driven by either separate drive or with drive from running rotor.

324. What is oil thrower ring?

This ring provided on the shaft in bearing

housing to make efficient lubrication.

325. What is the purpose of oil thrower ring?

It is used to lubricate the bearing effectively by splashing out lube oil quenched and rotates the contact motion of shaft while running.

326. What is oil scoop?

It is a small bucket shaped part fixed on

rotate able crankshaft

327. What is the purpose of oil scoop?

Used to splash lube oil intermediately for effective lubrication.

328. What is oil control ring?

A ring made of aluminium, brass or bronze fixed in the end covers of bearing housing.

329. What is the purpose of oil control ring?

The labyrinth grooved ring (oil control ring) used to avoid the leakage of lube oil to atmosphere and entry of moisture in to the bearing housing.

330. Why auxiliary lube oil pump is used?

Normally it’s a motor driven pumps used, 

1. To maintain the lube oil pressure when starting and running time, 

2. Auto start, incase of main lube oil pump failure, 

3. To give lube oil circulation when

the rotor is in ideal.

331. What is the casing bolt-tightening sequence?

332. What is torque wrench?

It’s a mechanical tool used for tightening the bolts of equipments with proper torques by the help of the torque indicator attached with it.

333. What is rotor run out?

Rotor run out defines the accuracy of trueness of the rotor. This should not exceed more than 0.002 inches.

334. How do you check rotor run out?

After keeping the rotor on the bearings or lathe center, with the use of dial indicator.

335. What are the various ways of impeller fixing arrangements?

1. Threaded, 

2.Sliding fit with key and lock nut, 

3.Snug fit with sleeve lock nut, 

4.With use of collets

336. What is the general value of rotor run out at various locations?

Impeller- 0.0025”

Sleeve – 0.0015”

Bearing – 0.001”

Coupling – 0.0025”

337. What is NPSH?

Net positive section head= static head + velocity head of liquid – vapor pressure at suction

temperature

338. What is NPSH required and NPSH available?

NPSH required establish the pump capability of working in minimum of positive suction head.

NPSH available establish the original working condition of pump in process with positive

suction head. NPSH available should be more than that of NPSH required.

339. What is cavitation?

Cavitation is the process of air or vapor lock in a pump. 

Reason for cavitation

1. Wrong NPSH

2. Pin hole or any air leak on suction line

3. Starvation of pump

4. Low velocity of liquid in the suction eye.

340. What is inducer?

A small low head, axial flow impeller that attaches to the conventional impeller is called as inducer.

341. Why inducer is used?

Inducer is used to increase the pump’s suction head (pressure), and prevent cavitation problems. 

The inducer will reduce the net positive suction head required of the pump or permit the pump to run at a higher speed.

Not all pump manufacturers have this feature available.

342. What is different between discharge head and discharge pressure?

Discharge head expressed in feet of the liquid being pumped from the discharge port.

The head varies depends on its discharge pressure.

Example:

 1 Psi liquid raises 2.32 feet of height of liquid with the specific gravity of 1.

Discharge pressure expressed as Psi.

343. What is minimum flow check valve?

Minimum flow check valve is a non-return valve with a regulating by-pass port in the application of high temperature (near saturation temperature on the discharge) liquid services.

Example- boiler feed water pump

344. Why minimum flow check valve is used?

1.Plugs

2.Springs

3.Bushes

4.Connecting Lever

5.Spindle

To avoid the backing of vapor lock in the

application of near saturation temperature liquid service by giving circulation of liquid while pump in ideal.

When the pump in ideal condition the by-pass

port opens and allows the circulation of liquid

and when the pump starts, the by-pass port

closes by the action of main check valve opening.

345. What is vertical in line pump?

The pump fixed in the line of flow of liquid itself in vertical axis called vertical in line pump. Actually it is a booster pump for giving extra energy to liquid while flowing.

346.How do you center the rotor and position the coupling of a vertical in line pump?

Normally this pumps have rigid muff split coupling attached with help of Allen screws, the shaft and coupling steps and grooves matched with together while fixing.

Add or remove the metal shims in-between the pump and motor frame for centering the rotor.

347. Explain the procedure for mechanical seal renewal of vertical in line pump?

1. To get proper work and safety aspect from operations

2. Remove coupling and before ensure the compression of seal unit by removing gland bolts.

3. Remove coupling and take out gland plate outside

4. Pull out compression unit (retainer) by special puller, care seal parts

5. Check the packing area of sleeve for fretting corrosion and confirm any other defects in sleeve

6. If the sleeve condition is good assembly of seal can start otherwise sleeve should be replaced by

the pump overhauling

7. Assemble is the same reverse procedure of the dismantle procedure before seen

8. While assembling the following aspects should be checked, retainer seating on sleeve slot with

lock pin perfectly, seal setting compression, bearing condition of the motor and alignment.

348. What is vertical sump pump?

Vertical pumps designed for suspension in or for mounting in their suction supply, like a sump or wet pit, are called as sump pumps. These are generally automatically controlled by float switches.

349. What is steady bearing?

Steady bearings are fixed in the vertical pump intermediately between the drop columns. It is actually bush bearing fixed in steady rest housing.

350. Draw the performance characteristic curve for a centrifugal pump?

351. What do you mean by balancing line in multi stage centrifugal pump?

The line connects intermediate labyrinth of balancing drum (discharge side) with the suction port for thrust balancing of rotor named as balancing line in multistage centrifugal pump.

352. What is the purpose of balancing line?

Used for thrust balancing by connects suction port and balancing drum.

353. Why mechanical seals are used?

a. Used for hazardous and toxic liquids, 

b. Zero leak proof, 

c. Reliable, 

d. Less friction loss comparing packing, 

e. High efficiency

354. How do you specify a mechanical seal?

As per API –682

X1 X2 X3 X4 X5

X1 –Balanced (B) and unbalanced (U)

X2 – single (S), double (D), tandem (T)

X3 – Type of seal gland (T- throttle bush, A- auxiliary sealing device)

X4 – gasket material (R- Graf oil)

X5 – face material (M – means tungsten carbide Vs carbon)

355. Name few seal manufactures?

John crane, Pacific, Borg Warner, Dresser rand, Dura metallic

356. What is 15WRS seal?

It is a seal made of john crane as per API – 610 in which the seat fixed on sleeve made of tungsten carbide the bellow seal face made of carbide with grafoil made secondary packings.

It has facility of flushing and quenching provision.

357. Name few types of mechanical seal?

1.Single coil mechanical seal, 

2.Multi coil mechanical seal, 

3.Balanced mechanical seal, 

4.Unbalanced

mechanical seal, 

5.Pusher/ non pusher mechanical seal, 

6.Single/ double mechanical seal

358. Draw a simple mechanical seal and name its parts?

1. Stationary component, commonly called 

‘the seat’.

2. Stationary component sealing member.

3. Rotating component.

4. Rotating component-sealing member.

5. Spring.

6. Gland Plate

7. Clamp Ring

359. Explain the complete dismantling and assembly procedure for a mechanical seal?

1. Remove the gland from stuffing box to access mechanical seal with care after checking the seal  setting compression.

2. Take out sleeve with retainer set and check any vision able effects like carbon crack, struck, wear  on facing area both carbon and seat

3. Remove the seat from gland and justify the condition of secondary packing of seat.

4. Remove retainer set by loosing Allen screws before make conform the retainer houses on the 

shoulder of sleeve other wise take measurement of retainer position.

5. Full view of inspection to be done on each and every mechanical seal parts like springs, thrust 

plate, drive lugs, snap ring, seat seating area on gland, sleeve surface due to fretting corrosion, seal  matting face of both seat and seal ring.

6. Changing new parts is better than reconditioning (lapping)

7. Assembling is the reverse procedure of dismantling on time the following aspects should be check: 

A. Square ness and rectangularity of seat after fixation on the gland plate.

B  Trueness of the shaft and sleeve.

C. Correct fit of wedge packing/ “O” ring with backup ring on the sleeve.

D. The recess confined with gland plate and stuffing box.

E  Seal setting compression as per drawings or as same before.

360. What is applicable standard for mechanical seal?

API – 682 (shaft sealing systems for centrifugal pump as well as rotary pumps)

361. What is the average life expected out of a seal as per API –682?

2 Years in normal working condition

362. What is seal setting compression?

The seal setting compression given by the retainer in to matting faces as per designed by the suppliers 

363. What is cartridge type of mechanical seal?

The seal is mounted on a sleeve that can be secured to the shaft from outside the seal chamber. 

It’s an advance-designed seal supplying by the seal manufacturers to make the installation easier. 

There is no need measurement while fixing and just changing as new set of cartridge seal instead of  reconditioning.

364. Can you change the seal settings compression of a cartridge type mechanical seal?

No.

365. Explain the assembly procedure of a cartridge type mechanical seal?

Is a simple and easy assemble procedure comparing a normal mechanical seal 

Just fix the cartridge seal set on the shaft and tight the gland plate with stuffing box. 

Tight the Allen screws on sleeve to lock with shaft then remove the seal setting lock plate provided on gland plate by loosening the sets screw.

366. How do you identify a balanced / unbalanced mechanical seal?

Identification of balanced seal: 

1. Stepped sleeve on seal ring area.

2. Reduced contact area of seal ring by the provision of step.

367. What is pusher/ non-pusher type mechanical seal?

When the secondary packing of seal ring is affected due to the thermal expansion in ambient condition and the axial end movement of rotor called as pusher seal. 

Otherwise called as non-pusher seal. 

Normally pusher seals are single & multi coil mechanical seals and non- pusher seals are bellow seals.

367. What are all the pre check to be made on a pump before starting positioning a mechanical seal?

Shaft true ness, Stuffing box bore square ness, Shaft deflection, Thrust movement of rotor, Dust free condition

368. What is stuffing box square ness?

It’s a process of checking the concentricity of stuffing box bore with shaft rotation by the use of dial indicator. The maximum allowable square ness is 0.0025”

369. How do you check stuffing box square ness?

370.What type of mechanical seal prefer for hot oil? Why?

Non-pusher seal (bellow seals) to avoid fretting corrosion due to thermal elongation.

371. What type of mechanical seal prefers sulphur duty?

Single coil mechanical seal with seal ring made-up of carbon and matting ring made – up tungsten carbide to with stand high temperature distortion and slurry service.

372. What is seal flushing fluid? Name few seal plans?

Seal flushing fluids used in the mechanical seal system for cooling, cooling and lubricating the mating seal faces.

373.What is seal quenching fluid? What is its purpose? Name few seal plans?

Seal quenching fluid used behind the mechanical seal system in the gland plate design provision to  avoid the hazardous or toxic liquid with atmosphere if the seal leaks in the form of liquid or gas state.

374.What is stuffing box cooling water jacket? Why it is used?

The integral or removable jacket provided in the pump for circulating the cooling water to maintain the stuffing box temperature into desirable limit for attaining the mechanical seal life reliable.

375. Why seal coolers are used?

To reduce the temperature of flushing fluid while entering into the mechanical seal system to maintain stuffing box temperature and better lubrication in the seal mating faces in running condition.

376. Name few MOC of seal faces?

Carbon

Tungsten carbide

Silicon carbide

Stellite

Ceramic

Bronze

Cast iron, etc.

377.What is seat ring and mating ring?

The ring has the provision (springs or bellows) to give seal setting compression called as seat ring.

The ring mates with seat ring for sealing called as mating ring.

377.How many elastomers are used in a mechanical seal assembly?

1. Between seat ring and sleeve or shaft, 2.Between mating ring and gland plate, 3.Between shaft and sleeve, 

4.Between gland and stuffing box.

378. Name few MOC of elastomers?

Neoprene, viton, glass/ asbestos filled Teflon, Graf oil, Buna-N, buna-S, etc.

379. What is snap ring in a mechanical seals?

Snap ring is a cut off circular ring used 

to hold seal ring with advance - compression. Snap ring rests on the groove made on retainer.

380. What are the usual problems faced with mechanical seals?

1. Sleeve fretting corrosion

2. Retainer springs struck

3. Seat or mating ring crack

4. Lack of reliable of secondary packing

5. Excessive wear of mating faces, etc.

381.Does the axial float have something to do with mechanical seal?

Yes. Seal setting compression will change.

382.What is double mechanical seal? Why it is used?

It is the two sets of simple mechanical seal. It is

used in the application of;

1. High hazardous of pumping liquid

2. Usage of separate flushing fluid

3. A seal leak could cause a pollution problem

4. The product is very costly

383 .Name two types of mechanical seal? Where is it used?

1. Back to back

The worst possible choice if used in the rotating seal version. Stationary versions

are acceptable because the sealing fluid is located at the outside diameter of the seal faces where we can take advantage of centrifugal force

2. Tandem

One seal behind the other requiring a low pressure buffer fluid between the seals. This

arrangement cannot be used if a higher-pressure barrier fluid is required or desirable.

384. What do you mean by barrier fluid? Name few barrier fluid?

Any time you use two seals in an application you will need a fluid between them. If the fluid between the seals is higher than stuffing box pressure we call it barrier fluid Water is a good barrier and buffer fluid.

385.What do you mean by buffer fluid? Name few buffer fluids?

If the fluid between the seals is lower than stuffing box pressure we call it buffer fluid.

386. What is the difference between barrier fluid and buffer fluid?

Any time you use two seals in an application you will need a fluid between them. If the fluid between the seals is higher than stuffing box pressure we call it barrier fluid. If it is lower than stuffing box pressure we call it buffer fluid. 

The liquid can be circulated either by forced circulation, a pumping ring or convection. The method that you will use will be dictated by the pressure, pump speed and shaft size. 

Water is one of the best barrier or buffer fluids because of its high specific heat and good conductivity. 

Petroleum oil is probably one of the worse because of its low specific heat and poor

conductivity

387.Where do we use cyclone separator in a mechanical seal?

In the application of the stuffing box pressure is more than the suction pressure of the pump to

separate the foreign materials if anything in flushing fluid from the discharge of the pump by the action of centrifugal force.

388.What is pumping ring in a mechanical seal? What is its purpose?

The thermodynamic grooves feature made on the ring or the circumference of the retainer of the seal system is named as pumping ring. 

This has two types of radial and axial pumping ring. Used to give circulation and pressure to flushing fluid

389.What is the difference between inside mounted seal & outside mounted seal?

The inside mounted seal

All components are in the pumping fluid.

Advantage: 

The elastomer can move to a clean surface as the seal face wears. Centrifugal force throws solids away from the seal components allowing the lapped seal faces to stay in contact 

Disadvantage: 

All the metal components must be corrosion resistant to the pumping fluid.

If the product solidifies or crystallizes when the pump is stopped, the seal can become inoperable.

The outside mounted seal

None of the metal components are in contact with the pumping fluid.

Most designs clamp to the shaft rather than using setscrews that damage ceramic or glass coated

shafts.

Advantage

This is the most common solution to non-metallic pump sealing.

Disadvantage

Centrifugal force throws solids into the lapped seal faces and can prevent the sliding components from moving freely. Higher pressure applications can cause the retaining clamp to slide on the shaft

390.What is seal balance ratio?

It is the ratio between the effective area of fluid pressure acting and the loading area of mating seal faces. It is actually defines the balancing of hydraulic forces.

391. What is the seal balance ratio for balanced/- unbalanced seal?

For balanced seal- 0.75; For unbalanced seal- 1.25 to 1.35

392.Differenciate centrifugal pump and reciprocating pump?

Centrifugal pump:

1. Working in the principle of centrifugal force

2. The main part is impeller

3. In the application of high capacity

4. Constant pressure with variable capacity

5. High efficiency

Reciprocating pump:

1. Working in the principle of reciprocating compression

2. The main part is piston/ plunger

3. In the application of high pressure

4. Constant capacity with variable pressure

5. Low efficiency

393.How do you measure Valve lift in a reciprocating pump?

In feather plate valve type the valve lift is equal to the thickness of the spacer used in-between seat plate and spring (cushion) plate; valve lift – 0.8 to1.5 mm. For the wing disc valve type it is the gap between disc top faces with the valve cover; valve lift- 3 to 6 mm.

394.What is the necessity of pulsation dampener?

To minimize the fluctuation of flow of liquid in the reciprocating pump (+ve displacement).

395.Name few types of pulsation dampener?

1. Bladder

2.Diaphragm

3.Mechanical

4.Bellow

396.How do you fill up gas in an accumulator?

Gas is filled in an accumulator by the use of flow regulator valve into the desired pressure, which is normally 40 to 70% of the working pressure of the line to be damp.

397.Explain overhauling sequence for a reciprocating pump?

Example Pump made: QUINTUPLEX WILSON

1. Get clearance from operation, drain out liquid and electrically isolate as per safety

2. Remove cylinder head cover, top cover and take out suction and discharge valves. Check any

damage of damage of valves and valve parts of all stages.

3. Remove plunger by rethreading with stub shaft and take out. Remove neck bush.

4. Dismantle stuffing box assembly include gland and packings. Take out cylinder head by removing bolts from crankcase frame.

5. Rethread stub shaft from cross head to take out

6. Open the crankcase cover behind after drain out crankcase lube oil

7. Dismantle coupling spacer to disconnect driver and free rotation

8. Remove connecting rod big end cup and split bearing and take out connecting rod with cross head outside from recess towards head side of all stages

9. Now only a part of crankcase with crankshaft available for further inspection.

10. Check crankshafts of any damage, web deflection, ply and thrust clearances. If you have doubted about any remark take out crank shaft from case and do necessary action to rectify.

11. Perfect inspection to be done on each and every part for any damage, score, marks, white metal pieces and tidy.

12. Assembling is the reverse procedure of dismantling and the following factors should be considered while and before assembling are valve lift, end clearance, neck bush clearance, cross head clearance, rod run out, cross head clearance, connecting rod big and small end bearing clearances, crank shaft main bearing clearance, web deflection, free rotation, alignment, etc.

398.What is web deflection? How do you measure web deflection?

Any movement of crank webs from their

ideal position during the 360-degree rotation of the crankshaft is web deflection. It is measured with the deflection meter or electronic web deflection system.

399. How to check big end bearing & small end bush clearance?

Big end bearing clearance:

Keeping dial indicator on connecting rod and lift it by a jack

Small end bearing:

By measuring outer diameter of gudgeon pin with inner diameter of bush in the small end or with the use of dial indicator or feeler gauge or plastic gauge which is adaptable.

400.What do you mean by stroke length?

The traveling length of piston/ plunger from BDC to TDC. It is the equal to the distance between crank pin center to crank shaft center.

401.What is gudgeon pin?

The pin, which connects the small  end bush of connecting rod with the piston or cross head.

The pin is well hardened to with stand tensile and compression load acting on the piston/ plunger.

402.What is crosshead slide/ shoe?

It is the two Babbitt lined adjustable shoes fixed to guide the reciprocal motion of the crosshead with an allowable clearance.

403.Name few ways of locking arrangement of piston/ plunger?

1. Threaded with locknut

2.Flanged bolted

3.Locked by pin

4.With split threaded coupling

404. How to ensure in-line concentricity of crankshaft to cylinder bore?

Keeping the two-dial indicators on the piston/ plunger rod with 90 degree of position and checking the deflection run out of the longitudinal movement of the rod on both sides when rotating crankshaft. The maximum deflection should be less than that of neck bush clearance otherwise the position of cylinder

bore with crankcase is adjusted to attain the reading with in limit.

405.What are dosing pumps?

These are all the tiny low capacity reciprocating plunger pumps.

406. Name few types of dosing pumps?

1. Simplex

2. Duplex

3. Multiplex

4. Single acting

5. Double acting

6. Horizontal

7. Vertical

407.Why dosing pumps are used?

Dosing pumps are used to pump a low capacity liquid injected into a high-pressure process operation.

408.What are the probable reasons for cylinder knocking in a reciprocating pump?

1. Valve seat or parts damaged

2. High temperature of pumping fluid

3. Foreign materials in suction area

4.Valve holder looseness

5.Plunger looseness

6.Air / gas mixed on liquid

7.Flow restriction, etc.

409.What are the probable reasons for valve knocking in a reciprocating pump?

1. Worn out seating area

2.Springs broken

3.Valve holder looseness

4.Improper valve lift

5.Valve loose by improper tightening

6.Reusing worn parts

7.Foreign matters in valves, etc.

410.What are the probable reasons for vibration in a reciprocating pump?

1. Foundation looseness

2.Cylinder or valve knocking

3.Misalignment

4.Worn parts

5.Failure of vibration dampener

6.Wrong installation and assembly, etc.

411. Where do we use screw pumps & gear pumps?

In the application of moderate pressure and capacity & constant capacity with variable pressure requirement.

412.What do you mean by flute?

Flute is a helical wave formed on the screws of the screw pump. In between the flutes pumping fluid passes.

413.What is idler screw?

The screw on the screw pump driven by the engagement of the flutes of the main screw coupled with prime mover.

414.How drive is transmitted to idler screw?

Through the engagement of the flutes of main screw of the screw pump.

415.How do you measure radial clearance & axial clearance between flutes?

Radial clearance; With the use of feeler gauge

Axial clearance; Keeping the dial indicator on the main screw shaft end and moving it longitudinally.

416.How do you measure gear backlash?

With the use of feeler gauge or dial indicator measurement reference with pitch diameter of the gear.

417.What is the usual gear hardness value?

Gears made of alloy- steel; maximum hardness value – 38 HRC & pinion 2 HRC more than gear.

Gears made of hardened alloy steel; surface hardness up to 60 HRC.

COMPRESSORS

418.Name few parts of a centrifugal compressor?

1. Rotor

2. Casing

3. Diaphragm

4. Diffuser

5. Labyrinth

6. Seal

7. Bearings, etc.

419.What is the applicable standard for centrifugal compressor?

API- 617

420.How do you specify a centrifugal/ horizontally split compressor?

MCL- horizontal split type centrifugal compressor, simply specify as ‘M’.

as per the design of BHEL.

421.How do you center a compressor rotor?

Measure the total float, which is the axial displacement of the rotor with out thrust bearing and with journal bearings on both sides to avoid the rest of rotor on the labyrinth edges.

Now the centering of rotor is the half of the total float while the thrust plate loaded on the active side of the thrust bearing and is achieved through:

1. Increase/reduce the width of centering spacer fixed behind the thrust plate

2. Machining on the active thrust bearing collar and adding spacer behind the in active thrust bearing

3. Add/ remove the shims on the thrust bearing if the adjustable requirement is less.

422.Explain the overhauling steps for a barrel type centrifugal compressor?

Compressor made: CLARK model: 2B F3

1. Proper safety clearance getting from concerned operation

2. Remove coupling spacer from driver, turbine or motor. Remove coupling by use of coupling puller like hydraulic puller or special tools

3. Before check the thrust clearance of the compressor shaft with thrust bearing

4. Before you to do remove the head should be check that all oil lines are dismantled

5. Remove cover and remove the instrument probe like thrust and radial probe with help of

instrumentation

6. Remove bearing housing cover and take care cover gasket for maintaining thrust clearance

7. Remove thrust bearing and thrust disc by removing of locknut

8. Remove split journal bearing two side and make mark, which side coming

9. Remove seals like floating seal with 3 rings. Remove shear ring by use of special tools and should be measure dimension were its locked and inspect the anti lock pin ok or not

10. Remove head locking shear ring and pull up the head by use of jack bolt and special puller. Use lifter to tight with head and transfer to safe place

11. Before removing the rotor, you should tight the diaphragm and rotor itself by use stud bolts for no need to remove one by one, pull out rotor with diaphragm to end position of barrel casing.

12.Use bellyband like clamp for holding and transfer the rotor and diaphragm to where you need. 

13. Remove split diaphragm and clean well. Check the rotor any damage and check the wear ring clearance, inter stage labyrinth clearance, rotor balancing, run out

14. Perfect inspection to be done on each and every part for any damage, score, marks, white metal pieces and tidy.

15. Assembling is the reverse procedure of dismantling and the following factors should be considered while and before assembling rotor run out, balancing the rotor and check the interstage labyrinth clearance, check the seals are properly seated, bearing clearance thrust and radial

423.How do you leak check a barrel type compressor?

The compressor pressurized to operating pressure by an inert gas like N2 . the shaft turn slowly with seal oil delta pressure 0.5 Kg/ CM2

 and leakage seal across HP seals is measured with this, it is possible to judge the fitness of the seals.

424. Explain the overhauling steps for a horizontally split type centrifugal compressor?

Compressor made: DEMAG model: 08 MH54

1. Remove coupling guard and coupling to disconnect from driver. Ensure auxiliary lines are disconnected from compressor like suction and discharge lines, lines for lube oil, seal oil, buffer gas, etc.

2. Remove bearing case of inboard with top split of compressor and remove end cover and out board bearing split case from the top split casing.

3. Let the top casing free and remove casing bolts and pulled up top casing using jack bolts

4. Provide guide rods before lifting to avoid any impact of parts and safe guarding labyrinth

5. Now we can check all viewed parts of rotor, diaphragm visually for any damage

6. Check free rotation, bearing radial and thrust clearance before dismantling and record readings

7. Dismantle and remove seals of both side and after bearing retainer and top bearing split house of both sides

8. Take out rotor from its position carefully

9. Remove bearing bottom housing and inspect each and every parts for any damage, score, rub, wear of labyrinths of all places, diaphragms, ports for seal oil, buffer gas

10. Recondition is better than changing new one. Keep always one rotor as standby to overhaul

11. While assembling fixation of seal should be followed after the top case boxed up. Use proper

sealing compound in-between joints of upper and lower casing.

12. Assembly is the reverse procedure of dismantling. The following factors should be checked while and after assembling are, labyrinth clearances of all areas, ports free condition, proper seating of parts and ‘o’ rings, clearance between seal rings and bushings, bearing radial and thrust clearances,

measurements with in design, free rotation, alignment, etc.

425.How do you check labyrinth clearance for a barrel type centrifugal compressor?

Securing the half split labyrinth with together by a hose clip firmly and checking the measurement

difference with use vernier or micrometers.

426.What is the compound used in the split half of the casing?

Copalite, key-paste, permatex, RTV-60.

427.Name the different types of labyrinths?

1. Conventional labyrinth seal

2.Straight type labyrinth

3.Stepped labyrinth

4.Knife edge labyrinth

5. J type labyrinth

6.Turbine type labyrinth

7.Honey comb labyrinth

428.How do you measure labyrinth clearance in barrel type compressor?

Securing the half split labyrinth with together by a hose clip firmly and checking the measurement

difference with use vernier or micrometers.

429.How do you measure labyrinth clearance in horizontally split type compressor? 

1. With the use of feeler gauge

2. Securing the half split labyrinth with together by a hose clip firmly and checking the measurement difference with use vernier or micrometers.

430.What is diaphragm?

It constitutes the dynamic profile of the stator parts of the compressor. Then are divided into three types viz. suction, intermediate and delivery. Suction diaphragm guides the gas to the first impeller.

Intermediate diaphragms have the function of transforming the kinetic energy into pressure, return to channel serves to guide the gas to the next impeller with shock less entry. 

It has contoured passage leading from the diffuser of one stage to the impeller of the next stage. 

Some diaphragms are constructed with baffled passages for the flow of coolant. Delivery diaphragm forms the diffuser for the last impeller and delivery spiral.

431.What is diaphragm delta P and what is the maximum value allowed?

It is the pressure difference between entry and discharge in diaphragm of fluid

432.What is balance piston?

The balance piston or drum fixed behind the last stage of impeller to take 90% of thrust load by gas and the thrust bearing supports the residual thrust.

In balancing piston the area in suction pressure side through balancing line is more comparing

discharge side of last stage of impeller. Labyrinths on the balancing drum effects to reduce leak off between the both sides of pressure acting.

433.What is balance piston delta P and what its normal value?

Practically it is the pressure difference of suction and discharge.

434.What is bridge over arrangement?

Bridge-overs are provided to reduce the number of compression stages and the omission of an impeller in the rotor assembly is

1. To provide an internal for a large side stream in connection

2. To make the critical speed of rotor out of normal operating range

3. To avoid interrupt of adjacent nozzle flanges each other.

435.Draw the lube oil circuit?

436.What is lube oil run down tank?

It is an overhead tank for lube oil to supply for bearing lubrication in case of emergency purpose when the both lube oil pump failured, designed still the rotor stops and coming into atmosphere temperature.

437.What is the normal filtration size of LO & SO filter?

Lube oil filtration size- 20 to 40 microns

Seal oil filtration size- 10 to 20 microns

438.What is the purpose of PCV?

The pressure control valve is used to maintain the pressure of the seal oil in the header line.

439.What is the purpose of LCV in the seal oil circuit?

The temperature control valve is used to maintain the level of seal oil in the overhead tank.

440.What will happen if PCV opens more?

1. The pressure of the seal oil header increases

2. The level in the over head tank increases

3. LCV tends to open more to lower the level of over head tank

441.What is flow through valve?

The recycle gas compressors are applied 3 rings seal configuration because of high sealing pressure.

However at start up operation handling gas pressure for regeneration is so low that insufficient seal oil quantity makes over heat of seal rings if seal system is used as is so, this is considered to solve such problem at start up operation by apply by-pass flow (flow-through) system with the use of a control valve called as flow- through valve.

442. Draw the seal oil circuit?

443. Why buffer gas is used in the seal oil circuit?

The buffer gas is an inert or non- hazardous gas used in the seal oil circuit to avoid the contact of

process gas with the seal parts and seal oil, if the process gas has hazardous or toxic or corrosive.

The buffer gas pressure is normally 7 psi more than that of process gas.

444.Is there any other source for isolating the seal oil from process gas?

Yes. Dry gas seal.

445.What is dry gas seal?

It is a non- contacting gas lubricated seal compressor seal with controlled buffer or flushing gas. 

They have a rotating seat with a broad face and V grooves. When the seat rotates, the V grooves force gas between the sliding faces. The resulting rise in pressure causes the sliding faces to lift off and run with out making contact.

446.Draw the performance characteristic curve?

447.What is polytropic head & polytropic efficiency?

Polytropic head (H);

The work usually required to compress unit gas flow along the polytropic compression curve is 

called polytropic head. i.e. actual head developed by the compressor.

Polytropic efficiency;

It is the ratio between the power required to develop polytropic head in to the power actually 

supplied.

448.What is surging?

Surge can be defined as the capacity below 55 to 70%, which the centrifugal compressor performance becomes unstable. 

When surging occurs, the high-pressure gas at the discharge of the machine flows back through the compressor in a complete reversal of the normal direction of flow causing the

collapse of pressure producing ability will repeat and cycle through the same sequence. Surging

controlled by;

1. Increase the flow from process to compressor suction

2. By-pass some discharge through coolers, back to suction of the unit

3. Decrease the pressure ratio.

449.What is stone wall effect?

Chocking or stone wall effect is in the large flow region, if the flow velocity reaches sound velocity anywhere in the compressor. 

The compressor can’t generate the head and all input energy are spend to over come the friction.

450.What is stalling?

Is a performance of vortex gas flow generated in the impeller internal or diffuser area as a symptom of surging when gas flow is decreased. 

To accompany this phenomenon, resonance of impeller and vibration sound (humming sound) will be generated. 

For corrective measure increase compressor flow.

Simply stalling means fluctuation in flow rate.

451. Draw a simple seal?

452.What is contact type & non- contact type seal?

The sliding faces of seal mating together when running called as contact type seal.

The sliding faces of seal with out mating contact with together when running called as non contact type seal.

453.Is the seal rings stationary, rotating or floating?

Floating.

454.How do you measure seal ring clearance?

With the use of vernier caliper or micrometers.

455.Does the seal ring have clearance with housing? Why?

Yes. Because of floating on its position.

456. What is the general value of seal ring clearance?

Inner seal ring (gas side) – 0.002 to 0.004 inches

Outer seal ring (oil side) – 0.005 to 0.006 inches

457. What is dummy bearing?

It is a temporarily made of aluminium or hylem wood bearing used to center the rotor with casing to avoid the fixation of original bearing while overhauling. Normally these are non lubricated.

458.What is honeycomb labyrinth?

The use of honeycomb labyrinths offers even better control of leakage rates (up to 60% reduction compared to straight pass type). 

It operates at approximately half

of the radial clearance of conventional labyrinth seals. 

It consists of S.S. foil about 10 mills thick. Hexagonal shaped cell make are enforced structure that provides a larger number of effective throttling points. 

In addition S.S. honeycomb retains its strength at high temperature and pressure levels, which would cause weakening of an aluminium labyrinth.

459.What is head?

Head used to close either side of the barrel and house the bearing end gas seals and oil seals made of solid forging. 

Depending gas medium either carbon steel or stainless steel are selected.

460.What is head puller?

It is arrangement of mechanical tool used to pull up head from the barrel of compressor on its position.

461.What is bellyband?

It is a large steel clamp fabricated to hold the full assembly of rotor with diffuser and diaphragm

housings with together for lifting and transporting the assembly safely.

462. Differentiate bundle ‘o’ring & head ‘o’ ring?

Bundle ‘o’ ring avoids the leakage between suction and discharge side of gas flow.

Head ‘o’ring avoids the leakage of discharged pressure gas into atmosphere. This ‘o’ring should be used with a back up Teflon ring to neglect extrusion due to high-pressure ratio.

463.What is hydraulic fit coupling?

The coupling can be fixed or removed in the shaft easily with hydraulic pressure by a separate hydraulic pump. 

This coupling has interference fit with shaft.

464.Draw a simple sketch to assemble & withdraw hydraulic fit coupling?

465.What is pusher pump & expander pump?

The pump connected in the jack to pull or push the coupling into shaft named as pusher pump.

The pump used to induce high hydraulic pressure between the contacting face of coupling and the shaft to make work easy named as expander pump.

466. Is hydraulic fit couplings with ‘o’ rings or with out ‘o’ rings?

With ‘o’ rings.

467.How do you ensure fit of taper coupling?

By the projection of the coupling face with the shaft end face. It is between 1/16 to 1/8 inches.

468.What is diaphragm coupling?

It is one of the flexible coupling used between compressor and steam turbine. 

All parts of this coupling are solidly bolted together, no moving or no wearing parts, therefore no lubrication is necessary.

469.What is active shim & store shim?

The shims connected on coupling with drive or driven hubs to transmit load with flexible named as active shims.

The extra shims bolted steady with coupling and these have not take the load of transmission named as store shims.

It should be fixed for the consideration of dynamic balancing of the rotor and add or

remove the shims in between the coupling depends span length.

470. What is shear plate coupling?

This coupling has the several of round plates with holes for bolting coupling spacer with hub

intermediately and it has be sheared & failured in case of high torsion force of drive exceeds ultimate limit. It is simply known as metal flex coupling.

471.Name different types of coupling?

Rigid coupling; 

1.Flanged coupling, 

2.Muff coupling, 

3.Threaded sleeve coupling, 

4.Four piece coupling (in Gould’s sump pump)

Flexible coupling; 

1.Metal flex coupling, 

2.Diaphragm coupling, 

3.Gear coupling, 

4.Grid coupling

472.What is the allowable vibration level as per API standard?

As per API 670; Vibration amplitude = root of (12,000 / RPM) mills per second.

473.Name few parts of a reciprocating compressor?

1. Cylinder

2. Piston

3. Valves

4. Cross head

5. Connecting rod

6. Crank shaft

7. Crank case

474. What is the applicable standard for reciprocating compressor?

API 618

475.What is top dead center? How do you measure it?

The end of transverse movement of the piston towards cylinder head is the top dead center of the reciprocating compressor. 

It is measured by keeping lead wire in the cylinder towards head end and rotating the compressor till the piston come back after compressing the lead wire. 

Now the top dead clearance is equal to the thickness of the lead wire.

476. Is there any means to increase TDC? How to do it?

TDC can be increased through;

1. Increase or decrease the thickness of the cylinder head gasket

2. Loose or tightening the piston rod in the cross head if threaded with piston rod locknut

477.What is bottom dead center? How do you measure it?

The end transverse movement of piston towards crankshaft end is the bottom dead center.

It is measured by keeping lead wire in the cylinder towards crank end and rotating the compressor till the piston come back after compressing the lead wire. Now the bottom dead clearance is equal to the thickness of the lead wire.

478.Why TDC is more than BDC?

For the consideration of thermal elongation of crank, connecting rod, piston rod towards the cylinder head side at working temperature.

479.What is rod deflection? How do you measure it? When will it increase?

It is the deflection of the piston rod from its trueness position while running.

Measuring: keeping two dial indicators on the piston rod with 90 degrees each of the recess in the distance piece of reciprocating compressor and measure the reading of indicator while rotating compressor. 

Deflection will increase due to

1. Accelerated wear and scuffing – piston to liner, piston rings, piston rod packings.

2. Broken rod

3. Damaged cross heads

4. Damaged pin bushings

5. Frame failure

6. Misaligned concentricity of cylinder bore with crank shaft.

480. Explain the overhauling steps for a reciprocating compressor?

Compressor made: BROOM WADE model: BW 2D

1. Disconnect all auxiliary lines like, discharge, air inlet, loader air, cooling lines

2. Decouple coupling to disconnect with driver and remove crankcase foundation bolts to transfer total unit to workshop for carrying overhaul

3. Remove the both suction valves with loader and discharge valves from head. Remove valve head.

4. Open all inspection doors provided and loose the nut connects cross head and piston rod and take out piston assembly with rod through head side. While removing care should be taken about piston rings falling.

5. Dismantle piston plates, piston rings, expander rings, wear band and rod.

6. Remove cylinder house with crankcase with distance piece. And disconnect distance piece

dismantle wiper packings and gland.

7. Remove wrist pin and take out cross heads.

8. Dismantle connecting rod big end bearing cover and remove split big end bearing and take

connecting rods outside.

9. Remove coupling hub and flywheel.

10. Remove lube oil pump connected with outboard of crankshaft and inboard cover

11. Remove main bearings of connecting rod top half and take out crank shaft outside

12. Remove bottom half of main bearings.

13. Now the complete dismantling has over. Perfect inspection of each and every parts to be done while and after dismantling of any damage, score, break, etc.

14. Better is changing new one instead of reconditioning damaged parts

15. Assembly is the reverse procedure of dismantling

16. When assembling the following factors should be considered are main bearing radial and thrust clearances, connecting rod big end bearing and small end pin clearance, web deflection, rod run out, wear band clearance, piston plate clearance with cylinder bore, bore surface finish, piston ring end and side clearances, piston end clearances, oil tubes condition, valve lift and passing, loader

piston freeness action, wiper packing clearance, free rotation and alignment.

481.What are the various clearances measured during overhauling of reciprocating compressor?

1. Piston end clearance, 

2.Piston ring side clearance, 

3.Piston ring end clearance, 

4.Diametrical

clearance between piston with cylinder/ liner, 5.Rider ring diametric clearance, 

6.Web deflection,

7.Piston rod run out, 

8.Connecting rod big & small end bearings clearance, 

9.Crank shaft main bearing

clearance, 

10.Crank shaft thrust allowance, 

11.Cross head with cross slide clearance, 

12.Gas & oil wiper packings clearance

482.What is cylinder to piston clearance? How do you measure it?

It is the diametrical clearance of piston outer with cylinder or liner bore.

It can be measured by feeler gauge or micrometers.

483.How do you check piston ring end clearance?

By inserting the piston ring in to the cylinder bore and checking the clearance of the piston ring ends with the use of feeler gauge.

484.What is difference between piston ring & bearer ring?

Piston ring, which used to avoid leakage from the piston end compressed gas to outwards through piston circumference.

Rider or bearer ring used to guide the piston movement and neglect the scuffing of piston with cylinder liner when the piston rings are damaged. It has less clearance with the cylinder bore.

485.What is the MOC of piston ring & bearer ring?

1. Cast iron,

2.Carbon, 

3.Bronze, 

4.Teflon, 

5.Phenolic

486.How much the normal clearance between piston ring to piston groove?

It simply specified as piston ring side clearance

For MOC of cast iron, bronze, carbon – 0.001 inches

For MOC of Teflon – 0.012 inches

487.Name different types of gas packing rings?

1. Pressure breaker ring

2. Radial cut ring

3. Tangential cut ring

4. Anti extrusion ring

488.What is pressure breaker ring? Where it is located? Which one is pressure breaker ring?

This is the simplest form of packing ring acts to break or slow down gas passage only with out actually sealing it completely. 

This prevents damage to packing rings and garter springs due to the shock effect

of the differential pressure involved.

It has a limited clearance at the cut only and should not exceed more than 0.010 inches per inch of bore diameter. 

Obviously this ring should not be allowed to operate with out end clearance because its

life would be very short. This ring located in prior towards gas side.

489.What is sealing ring? Where is it located? Which one is sealing ring?

The true sealing ring made up of a pair of rings, the first of which is radially cut with considerable clearance at each end. 

The second ring is tangentially cut forming an overlapping seal joint that prevents gas passage from the outside periphery toward the rod bore. 

The inner radial cuts of this tangent ring are arranged so that they occur approx. between the radial cuts of the first ring in the pair.

In this manner, gas passage along the rod is blocked so that there is no through escape.

This type of ring is single acting or directional in that it seals pressure from one side only.

490.Draw a tangential cut ring and mark the clearances?

491.Draw a radial cut ring and mark the clearances?

492. Is there any clearance between cup to packing? Why that clearance is given?

Yes. This clearance given for

1. Space for oil film lubrication

2. Shock effect of the differential pressure involved

493. What is the MOC of gas packing rings?

1. Tetra fluro ethylene, 

2.Carbon, 

3.Bronze, 

4.Teflon, 

5.Babbitt material, 

6.Cast iron

494. What are various methods of capacity control?

1. Speed regulation, 

2.Suction throttling, 

3.Holding inlet valve open, 

4.Clearance volume variation

495.What is clearance pocket?

Clearance pocket made up of a cylinder with a piston to regulate the capacity in high-power

compressor by varying the clearance volume. 

It can be operated manually or by automatic means and divided into two types of

1. Constant clearance pocket

2. Variable clearance pocket

When this pocket in operation the compressor neither draws in nor delivers any gas: both valves are closed and a constant amount of gas is expanded and compressed in the cylinder.

496.What is suction unloader?

It is a pneumatically operated piston-type device overcomes the tension of a spring and moves down the rod of the piston like element terminates in fork, the prongs of which will keep the inlet valve plate off the seat. 

As a result no gas will be compressed and delivered because the inlet valve will be open,

and the will be pushed out of the cylinder into the intake line until the air pressure relived in the piston of unloader. 

Thus the compressor capacity is reduced by skipping the discharge strokes.

497.Draw a simple suction valve and name its parts?

1.valve stud 

2.self locking nut 

3.collar

4.valve seat plate 

5.plate spring 

6.valve

7.valve guard 

8.centring sleeve 

9. ‘O’ring seal

498. Draw a simple discharge valve and name its parts?

499.How do you recondition the valves of a reciprocating compressor?

The main work of reconditioning the valve is to make the seating area of plates in perfect appropriate level by lapping. 

Out of this well vision able inspection of valve plate, seat plate, lock screw and the

condition of springs should be adapted.

500. How do you leak check a valves of a reciprocating compressor?

1. Liquid filled observe for 1.5 minutes and slots of seat must still be half full

2. Leak check by connecting to metered air supply system.

501.Second stage discharge pressure is high? What is the problem? How will you identify?

Causes

1. Inter cooler between second and third stage or after cooler has not effective cooling – feeling

cooling water circulation

2. Unloader not working – check the unloader spindle position any marked

3. Second stage discharge valve not opened properly – feel temperature of valve

4. Improper piston end clearance

5. Third stage suction valve not opened – checking with stethoscope

502. There is a capacity reduction in the compressor? What is the problem?

1. Suction valve damage/passing

2. Discharge valve damage/passing

3. Clearance pocket may be in open condition

4. Unloader loaded

5. Damage piston rings or packing rings

6. Excessive piston end clearance

7. Speed less

503. There is a reduction in the discharge pressure of the compressor? What is the problem?

1. Suction valve damage/passing

2. Discharge valve damage/passing

3. Clearance pocket may be in open condition

4. Unloader loaded

5. Damage piston rings or packing rings

6. Excessive piston end clearance

7. Speed less

504.What is the normal pressure ratio of discharge to suction?

14: 1

505.Why intercoolers are used?

a. Remove heat of gas taken by compression

b. Reduce the volume of gas consistence to other stage

c. Save in power

d. Increase efficiency

506.What is distance piece?

This piece with inspection doors fixed in between compressor cylinder and the cross slide house. It accomplishes space for gas packings gland and wiper rings through inspection door. Drain line attached bottoms of it for identification incase of gas or oil leakage if any.

This can be aligned with cylinder or crankcase with measurement of rod deflection.

507.What is oil wiper packing?

Wiper packings fixed on the piston rod in the side of cross slide to avoid the leakage of oil outside and avoid the entry of gas into crosshead area incase of gas packing rings leakage. These packings are same like gas packing seal rings.

508.Why intermediate gas packings are used?

In the case of double acting compressor, compression takes place on the both side of piston. 

Front side of piston is sealed by covering cylinder head and the other side it can’t possible because of the presence of piston rod. So a special type of sealing system used with the number of set of sealing rings. 

It is not a zero sealing system so purge gas to be provided behind of sealing ring sets to avoid

the passing of hazardous compression gas out from cylinder. These sealing ring packings are called as intermediate gas packings.

509.What is cylinder jacket?

The jacket made with cylinder integrally or passage sealed with cylinder liner ‘o’ rings

For removing heat from gas by compression and friction heat of piston rings.

510. What is stuffing box jacket?

Cooling water circulated jacket provided in gas packing stuffing box for removing heat generated through the friction of packing rings with piston rod.

511.How the cooling water is prevented from entering the gas side?

With the use of ‘o’ rings on cups of stuffing box.

512.What is volumetric efficiency?

It is the ratio of the actual capacity of the compressor to displacement (swept volume) and is expressed as a percentage.

513.What is need for cylinder liner? What is its MOC?

Cylinder liner is used to avoid the change of cylinder or major recondition incase of high scuffing due to friction with damage or broken piston rings.

Liners are normally made of cast iron.

514.What is cylinder liner lubrication?

A force feed lubrication given to cylinder liner to minimize the friction with piston rings is called

cylinder liner lubrication.

More lubrication causes the discharge valve plates to stick.

515.How do you lubricate the cylinder liner?

Force-feed lubrication by lubricator pumps given into the center of stroke length in the cylinder port provided.

516.Explain the procedure for liner removal?

Compressor made: CLARK model: CRA, 40T

1. Remove head, piston and piston rod

2. Remove stuffing box packing assembly

3. Take out cylinder from its position with distance piece

4. Keep cylinder in vertical position that the head side in bottom

5. Fix liner puller and pulling jack with a block loading the liner

6. Pull out liner downwards by hydraulic jacking

7. If the fitness is more steam jacketing in cylinder and dry ice in the liner should be carried for easy removal due to expansion of cylinder and contraction of liner while jacking.

517. What is single acting, double acting and balanced opposed?

Single acting: 

Compression of gas takes place in one side of the piston only.

Double acting: 

Compression of gas takes place on both sides of the piston.

Balanced opposed: 

Two set of piston and cylinder arrangement made in the single crank shaft horizontally 180 degree oppose for dynamic balancing and admit of rotative speeds higher than other types.

518. Name few parts of a steam turbine?

1. Casing

2. Running wheel

3. Nozzle

4. Labyrinth or carbon seal

5. Trip and throttle valve

6. Bearings

519. What is the applicable API standard for steam turbine?

API – 619

520.Explain the overhauling steps for a steam turbine?

Turbine made: TERRY model: Z-1

1. Isolate steam inlet, remove coupling guard and coupling spacer to disconnect from driven

2. Dismantle governor and linkages with governor valve

3. Loose the bolts connecting top half split casing with bottom casing and take out.

4. Remove bearing covers on both side inboard and inboard

5. Remove leak-off lines of carbon ring housings

6. Take out rotor with stuffing box and transfer to workshop to carry further overhaul

7. Dismantle stuffing box case and carbon rings and journal bearings

8. Remove governor drive coupling, trip collar, ball bearing, steam bunters on outboard side

9. Remove coupling hub and steam bunters on inboard side

10. Loosen wheel lock nuts with noting proper position of wheel and remove the wheel from the shaft with the use of arbor press

11. Perfect inspection should be carried on each and every parts incase of any damage, score, brake

12. Assembly is the reverse procedures of dismantle. Use proper sealing compound in-between casing split and bearing housing cover.

13. The following factors should be considered while and after assembling are, shaft run out, nozzle and reversing chamber condition, governor valve and trip functioning, journal bearing radial clearance and crush, carbon ring clearance, governor function, free rotation, alignment, etc.

14. Trip check should be checked before coupled with driven.

521. What is regulating valve or governing valve or chest valve?

It is a special designed throttle valve used to control the flow of steam into turbine through open or close signal gotten from governor to maintain the speed of the turbine stable.

522.What is TTV or MSV?

TTV- Trip & Throttle valve is a combined valve of both trip shut off and throttle together

construction. 

Trip valve is shut off when the speed of the turbine exceeds limit suddenly and the

throttle valve controls the speed of the turbine as per speed set on governor. 

This valve is normally

used in low or medium load turbines.

MSV- Main shut off valve is a trip valve used to cut off steam suddenly when speed or any abnormal condition of turbine exceeds except than throttling. 

The throttling or chest valve is separately fixed

after MSV to maintain the speed. Normally this valve used in heavy load turbines.

523. What is nozzle box?

The blades form short arc nozzles they are mounted in a blade carrier ring which is secured to the casing called as nozzle box.

524. What is nozzle?

In impulse turbine the nozzles are fixed at the inlet end and steam passes through these converging nozzle passages, which reduce its pressure by increasing velocity progressively converting heat energy into kinetic energy.

525. What is fixed blade and moving blade?

Fixed blades are stationary blades fixed in the casing. Moving blades are fixed on the running wheel in the design of reaction turbine. The drop in pressure takes place in the fixed and moving blades, falling gradually through out the turbine.

526. Where to measure moving blade to fixed blade clearance?

In between the moving blades on the running wheel and the fixed blades of carrier ring, downstream side of steam flow in moving blades. This clearance measured after pulling rotor ‘up stream’.

527.What are the various clearances measured in a rotor?

1. Labyrinth clearance

2. Carbon rings clearance

3. Bumping clearance

4. Bearing clearance

528.How do you assemble carbon packings? What is anti rotation pin?

The segmented carbon packing rings fixed on the rotor shaft hold by a garter spring with a less

clearance about 0.001 inches in cold condition.

The carbon rings are prevented from rotating by a tang or pin named as anti rotation pin. The thermal expansion of carbon is less than that of steel.

529.How do you center a turbine rotor?

The turbine rotor centered according bumping clearance between fixed and moving blades.

This can be achieved by add or remove shims behind the thrust collar.

530.What are the different types of labyrinth in a turbine rotor?

1. Conventional labyrinth seal, 

2. Straight type labyrinth, 

3.Stepped labyrinth, 

4.Knife edge labyrinth, 

5.J type labyrinth, 

6.Turbine type labyrinth

531.How do you check bumping clearance?

By the use of feeler gauge.

532.What is internal casing?

It is a guide blade carrier and inserted with its circumferential groove in to a corresponding supporting web of the outer casing. The web is also used for axial positioning.

533. What is internal clearance? Why it is necessary? Explain the procedure?

Internal clearances between moving and guide are required for compensating thermal expansion and to provide running clearance.

Owing to a virtually symmetrically design of the inner casing, all its cross- sections show practically the same amount of expansions.

Substantial thermal stresses in the inner casing needn’t be expected, because its outer and inner walls are exposed to almost the same temperature.

534. Explain the procedure of carrying out optical alignment? What is its advantage?

Fix the laser transducer and the reflector frame with the use of chain type bracket. 

Connects the connecting cable between transducer and control unit, which consists LCD monitor, entering keys of dimensions of foot length of movable machine. Enter the foot lengths in the control unit. 

Little shaft rotation required determining alignment, obtaining accurate alignment results with as 60-degree shaft rotation.

Finding out the result is simple by the three key operation of 

1. Enter dimension, 

2. Rotate shafts, 

3. Read results. 

Add or remove shims on front or and back feet of movable machine till achieving best

alignment results.

Advantages: 

1.easy operation, 

2.accurate, 

3.little shaft rotation is enough, 

4.online measurement can take all these elements into account and yields accurate repeatable thermal growth.

535.What is a governor? Name few types?

Governor is a device, which senses the speed of turbine and controls the steam to the turbine to

maintain the speed at a desired level to meet changes in load or steam flow.

Types:

1. Mechanical governor

2. Combined mechanical and hydraulic governor

3. Instrument governor

4. SG (simple governor)

5. TG (turbine governor), etc.

536. What is minimum and maximum governor speed of a governor?

The minimum and maximum speed set in a governor; in between of that speed only governor takes its control of the running machine to maintain speed constant.

To match the governor speed we would use speed step up or reduction gear mechanism in turbine of high speeds.

537.What is Woodward PGPL & SGX governors?

Both governors are controlled by pneumatic air pressure. 

PGPL used in high speed turbines with speed reduction gears. 

The actual speed of the governor is step down with the speed of the turbine.

SGX governors used in low speed turbines coupled directly with a flexible coupling.

538.Explain a problem faced by you in a governor & how did you overcome?

Problem- governor hunting

Overcome- changing new oil to full level

539.What is speed droop governor?

It is a governor with the facility of adjustable (variable) droop mechanism to run the machine at maximum droop with the difference load operational condition. Example- UG 8 woodward governor.

540.What is isochronous governor?

The governors are capable of operating at zero droop called as isochronous. An isochronous governor will maintain a constant speed up to 100% load. When an increase of load is placed on a turbine the actual speed will decrease temporarily. 

The governor will increase the steam to bring the turbine back to the original speed and carry the larger load. If a load is removed from a turbine, the speed will increase temporarily. 

The governor will decrease the steam to bring the turbine back to the original speed and carry the smaller load.

541. A governor is hunting? What are the on line & off line adjustments that can be tried?

Online: Changing new oil up to full level

Checking link freeness Clearing linkage looseness if any Setting valve travel correctly with governor linkage 

Offline: Adjust speed droop Checking worn out parts and correcting

542.What are the various trip systems available in a turbine? 

Over speed

Low lube oil pressure

Rotor displacement

High lube oil temperature

High vibration

543.How do you check OST in a turbine? How do you adjust OST?

When checking OST in a turbine, which should be decoupled from the driven unit to avoid the pump to run in the speed more than normal design and it is dangerous act so.

Run the turbine until over speed by allowing more by pass steam out of governor control to check the action of over speed function properly.

If it is not proper trip need to adjust by increase or reduce the spring force of over speed weight

through fastening adjusting screw to vary the desired over speed.

544.Why LLO trip is given for a turbine?

When the lube oil pressure comes down results the rapid damage of journal bearing due to insufficient lubrication and cause severe injure of equipment and environment. so for low lube oil trip should be given for a turbine. LLO trip actuate the latch cylinder of MSV to disconnect and the valve close suddenly to shut off the flow of steam. The turbine turns to idle trip position.

545.What is extraction cum condensing turbine?

From the outlet of steam from turbine, one part of steam is used for process operation with constant pressure and the other residual part of steam condensed by a condenser called as extraction cum condensing turbine.

546.What is the control mechanism for extraction cum condensing turbine?

Askania control mechanism.

547.What are the various parameters to be noted down for the above hydraulic circuit?

1. Speed control device

2. Pressure control system

3. Tripping device

4. Extraction control limit

548.What is gland ejector? What is ejector condenser?

Both ejectors are used in condensing turbine design which outlet pressure of steam is less than that of atmospheric.

Gland ejector is used in the gland area of the turbine for positive flow of leak off steam to atmospheric and to avoid the entry of atmospheric air into turbine.

Ejector condenser used in the surface condenser of turbine for sucking the steam from outlet, which pressure is less than atmospheric into the condenser.

549. What is hogging ejector? What is start up ejector?

Hogging ejector is a start up ejector to create the vacuum pressure in the outlet of turbine while

starting up the turbine pertaining positive rotation.

550.What are the auxiliaries for a steam turbine?

Ejectors, Condensers, Orifice, Lube oil filters/ coolers, Overload steam nozzles, Traps, Governors, etc. 

551.What is thrust collar?

It is a circular ring formed integral or fixed on the rotor shaft of the turbine. It is loaded on thrust bearings both side with a thrust clearance about 0.008 to 0.015 inches to take thrust load of rotor.

Rectangularity and the surface roughness of thrust collar should be care when fixing.

552. How is tachometer drive taken from the rotor?

Through the 50 or 60 teeth gear fixed on the rotor when the current frequency of tachometer is 50Hz or 60Hz respectively. 

A proximity probe provided with a magnetic sensible gap to sense the tooth of gear rotation and converts into number of revolution by electrical signal and shows on monitor.

553.What is pedestal trip?

It is a hydraulic trip device used to shut off trip valve when the turbine reaches over speed.

When the over speed trip weight actuate the trigger of spring loaded piston to release from its position cause a sudden pressure reduction by connecting the latch cylinder pressure oil of trip valve to drain.

The result of sudden latch disengages cause the trip valve to close immediately.

554.What is impulse and reaction turbine?

Impulse turbine: 

These are fitted with nozzles at the inlet end and steam passes through these converging nozzle passages, which reduce its pressure by increasing velocity progressively converting

heat energy into kinetic energy. Impulse rotor blades inlet edges set at an angle of 15 and 30 degree to the direction of rotation. 

The steam then leaves the blades at a similar angle to that of its energy. In impulse turbines the entire drop in pressure takes place in fixed nozzles, the pressure through out the stages remaining constant. 

High pressure service and have little end thrust on the rotor. It has high vibration of wheels.

Reaction turbine: Pressure drops in gradual and takes place continuously over the fixed and moving blades. 

In fixed blades velocity increases, the pressure of the steam falls as it passes over the moving

blades. 

The fixed blades correspond to nozzles, they change the direction of steam towards the moving blades, at the some time allow it to expand to a higher velocity. It is a simple, sturdy construction with less vibration and efficient in low-pressure service. 

Dummies require to reduce steam thrust on the end of the rotor. The fine blade tip clearances necessary are liable to cause stripping of the turbine.

555.What is static electricity?

It is a one method of generating electricity by the frictional contact of two dissimilar polarity elements,as the charge placed upon a glass rod by rubbing with silk or fur. It is the electricity at rest.

556.What is electrical run out?

Electrical run out refers to the apparent displacement measured by proximity probes, such as eddy current sensors, when monitoring a rotating shaft—but this displacement is not due to the actual physical movement of the shaft or a defect in its shape; instead, it arises from variations in the shaft's electrical properties, such as conductivity or magnetic permeability across its surface, which can affect sensor readings as the shaft rotates

557. What is gauss meter?

It is an instrument used to find out the density of magnetic flux.

558.What is pressure compounded & velocity compounded turbine?

Pressure compound: 

In which the steam pressure is dropped in number of stages of the turbine that is

the total pressure drop does not take place in the first nozzle ring but divided up equally between all the nozzle rings. To minimize heavy end thrust when the steam exists high pressure on inlet side, dummy piston is used.

Velocity compound: 

The steam is expanded through the sets of nozzles to a high velocity and is then

passed over the first moving blades. Only a portion of this high velocity is absorbed by this moving blade. 

The reminder being exhausted on to the next ring of fixed blades in the way of arc nozzles,

which change the direction of the steam with out affecting velocity and the steam is passed on to the next ring of moving blade. This process repeated until the total velocity is absorbed. The steam flows through the blades, the pressure remains constant, so there is no large end thrust to be balanced as the steam thrust acts in a rotary direction only. 

589.How do you demagnetize a rotor?

With the use of carbon slip ring brush

590.What is earth brush?

Through spring loaded carbon brushes which connected with earthing system properly

591. What is the compound used in the split half of the casing?

Coat of cement from ‘copallite’ and lay two threads of shoe maker’s twine or asbestos yarn around the joint approximately ¼ inches apart.

592.What is the principle of bolt heater?

Removals of high torque tighten bolts through elongation of bolt by the induction of heat transfer with the use of bolt heater.

593.What is centrifuge? Why it is used?

It is a machine used to clarify and purify the lube or seal oil to maintain the quality (flash point) of oil with in control. It removes contaminated unwanted gas, air, liquid (water) and solids from the circulated oil in the system by the principle of centrifugal force.

594.What is the filtration size of normal LO filter?

25 microns.

FINFANS

595.What is finfan?

To cool the fluids through fined air-cooled tubes with intensity of positive flow of air from a fan called finfan.

596.What are the various measurements to be taken on finfan?

1. Blade angle

2. Tip track

3. Bearing thrust allowance

4. Fit of fan hub and sheaves with shaft

5. Alignment of belt drive

597.How do you measure blade angle? What is the instrument used? How do you adjust?

Measuring angle with the use of bevel protractor positioned on the blade one-inch distance from the tip of blade. Angle is adjusted by releasing blades free to rotate from hub.

598.How do you measure tip track?

Tip track is the difference in the same line of rotation in the tip of all blades.

It is measured by marking line the end of blade with frame.

599.What is FRP blade? What is its advantage?

FRP – Fiber Reinforced Plastic, coated on sheet metal formed fan blade.

Advantages – less weight, high strength of bending and low cost.

600. What are the various methods of fixing the blade to hub? 

1. By hub split clip locking

2. Flanged bolted with slotted hole

3. Tensioned bolted with segmented lock rings

601.What are the various methods of drive arrangement available for finfan?

1. Direct couple with motor shaft

2. Belt drive

602.What are the PM jobs carried out on a finfan?

1. Periodic vibration measurement, 

2.Lubrication of fan bearings, 

3.Checking belt condition

4. Measuring any noisy operation