1. What is Absolute Pressure?
The existing gauge pressure plus atmospheric pressure. At sea level the gauge pressure in
pounds per square inch is 0 PSI. Adding 14.7 gives the absolute pressure in pounds per square inch (PSIA).
This is a pressure measured from a base of absolute zero. We breathe air at a pressure of approximately 14.7 pounds per square inch absolute (psia).
We don't notice this pressure because it is always around us and its called atmospheric pressure.
However, if we look at an unused pressure gauge it reads 0 psi. The absolute pressure of a system therefore equals the sum of Atmospheric Pressure and Gauge Pressure. See PSIG.
2. What is Absolute Temperature?
The temperature of a body referred to the absolute zero, at which point the volume of an ideal gas is theoretically zero. (absolute zero = - 459.67°F / - 273.15°C).
3. What is Activated Alumina?
An adsorption type of desiccant used in some desiccant dryers.
4. What is Adiabatic Compression?
A type of compression where no energy transfer as heat is transferred to or from the gas during the compression process.
5. What is Adsorption?
The accumulation of gasses, liquids or solutes on the surface of a solid or liquid. This term is often used when describing the action of desiccant dryers. Not to be confused with "absorption".
6. What is Adsorbent Filter?
A filter medium primarily intended to hold soluble and insoluble contaminants on its surface by molecular adhesion.
7. What is Air Plant Capacity?
"Standard Cubic Foot," or its abbreviation "SCF," used as a measure of Compressed Air means
that quantity of dry air (0% RH) which in gaseous form would occupy a volume of one cubic foot at 60 degrees Fahrenheit temperature and 14.70 pounds per square inch absolute pressure. One thousand SCF shall be abbreviated herein as "MCF".
8. What is Air Receivers?
Steel tanks in to which the compressed air or gas is discharged from the compressor.
Receivers help to eliminate pulsation in the discharge line (for reciprocating compressors) and also act as storage capacity during intervals when the demand exceeds the capacity of the compressor.
Use proper size tank as furnished and/or recommended by manufacturer.
Do not reduce tank size or restrict discharge air line from compressor tanks.
9. What is Aftercoolers?
Heat exchangers that remove the heat of compression of the air or gas after compression is completed.
They are also one of the most effective means of removing moisture from compressed air. Compressed air normally contains some moisture which can cause damage to air devices.
Aftercoolers, which assist in removing this moisture by lowering the temperature of the air, can be either of the water-cooled or the air-cooled type.
10. What is ANR?
Atmosphere normale de reference. The term ANR is not usually applied to cfm, it is the new European replacement for Free Air Delivered (FAD) and usually follows the metric measurement of air flow, such as Cu Meters per Minute ANR.
11. What is Asset Monetization?
When a company like an energy service provider builds, buys, owns, maintains and operates your existing energy systems or equipment.
12. What is Axial Compressor?
An aerodynamic machine, usually multistage. The air is drawn through a series of rotors (propeller like) and stators until the desired working pressure is achieved.
It is called axial because the air essentially enters one end of the compressor and is ejected at pressure from the other end.
This type of compressor is usually applied to very high capacity compressed air requirements.
13. What is Bar?
A unit of pressure equal to 1,000,000 Dynes / cm2 , 0.99 atmospheres.
A measurement of pressure, 100kPa = 1 bar.
This corresponds very closely to 1 atmosphere and the two are often confused.
1 bar = 14.504 psi.
1 atmosphere = 14.7 psi.
14. What is Barometric pressure?
Is the absolute atmospheric pressure existing at any given point in the atmosphere.
It is the weight of a unit column of gas directly above the point of measurement.
It varies with altitude, moisture and weather conditions.
15. What is Base Air Requirement (BAR)?
The quantity of compressed required by the customer to meet normal system demand as defined in Standard Cubic Feet per Minute (SCFM).
The BAR is established to cover the maximum requirement of the customer during the normal production cycle.
16. What is Base Monthly Facility Fee?
The "Base Monthly Facility Fee" is a fixed monthly charge to supply the Base Air Requirement.
17. What is Bernoulli's Principle?
In physics, the concept that as the speed of a moving fluid (liquid or gas) increases, the pressure within that fluid decreases.
Originally formulated in 1738 by the Swiss mathematician and physicist Daniel Bernoulli, it
states that the total energy in a steadily flowing fluid system is a constant along the flow path. An increase in the fluid's speed must therefore be matched by a decrease in its pressure.
Bernoulli's principle applies in nozzles, where flow accelerates and pressure drops as the tube diameter is reduced.
It is also the principle behind orifice or Venturi flow meters.
These meters measure the pressure difference between a low- speed fluid in an approach pipe and the high-speed fluid at the smaller orifice diameter to determine flow velocities and thus to meter the flow rate.
Bernoulli's principle is sometimes mistakenly used to explain the net force in a system that
includes a moving fluid, such as lift on an airplane wing, thrust of a ship's propeller, or drifting of a spinning baseball.
The principle, however, only applies to systems that do not produce a net force.
18. What is Blower?
A compression device that is designed to discharge at lower pressures.
Usually a blower discharges below ratios, although this figure can vary based on manufacturer.
19. What is Booster Compressors?
Machines for compressing air or gas from an initial pressure, which is above atmospheric pressure, to a still higher pressure.
20. What is Boyle's Law?
States that the volume of a gas, held at a constant temperature, will vary inversely with the pressure.
21. What is Brake Horsepower?
The actual or useful horsepower of an engine, usually determined from the force exerted on a friction brake or dynameter connected to the drive shaft.
22. What is Breathing Air?
Be careful with this! Not all compressor systems can produce breathing quality air.
The compressed air requires special treatment to meet OSHA Grade D breathing air requirements. Leave the supply of breathing air to experts.
23. What is British Thermal Unit (BTU)?
The quantity of heat required to raise the temperature of one pound of water from 60° F to 61°F at a constant pressure of one atmosphere.
24. What is Bypass Valve?
An automatic or manual valve that causes the flow to be vented. In centrifugal compressor applications this valve is also referred to as a blow-off valve.
25. What is Celsius ( °C)?
Also known as the centigrade scale. The international temperature scale where water freezes at 0 (degrees) and boils at 100 (degrees).
26. What is Clean Room?
An enclosure in which air characteristics such as temperature, humidity, contamination and pressure are maintained at a specific level.
27. What is Clean Pressure Drop?
The pressure drop across a filter element as measured under steady state flow conditions using a clean test fluid across a clean filter element.
This is not necessarily the pressure drop that will be realized by a clean filter in an actual operating condition.
Clean, wetted pressure drop should be specified to better understand the actual operating characteristic.
28. What is Closed Loop System?
A cooling system used with the CDA AIR Stations. The system in which a glycol/water and corrosion inhibitors are circulated through a air to coolant heat exchanger and storage tank in a closed loop.
Heat picked up from the compressors by circulating fluid is transferred to the atmosphere through the heat exchangers.
29. What is Closed Loop Evaporative System?
The same as the closed loop cooling system with the addition of spray bars.
During periods of high ambient temperature, water is sprayed on the air to coolant heat exchanger.
Evaporative cooling increases the heat exchanger's effectiveness, reducing the temperature of the coolant returned to the compressor.
30. What is Cogeneration?
1. Any of several processes that either use waste heat produced by electricity generation to satisfy thermal needs, or process waste heat to electricity, or produce mechanical energy.
2. The use of a single prime fuel source in a reciprocating engine or gas turbine to generate both electrical and thermal energy to optimize fuel efficiency.
The dominant demand for energy may be either electrical or thermal. Usually it is thermal with excess electrical energy, if any, being transmitted into the local power supply lines.
31. What is Competitive Transition Charge (CTC)?
A non-by-passable charge representing the transition cost assessed to recover the reasonable uneconomic portion of the costs associated with
1. Fixed costs from generation units
2. Costs associated with existing purchase power commitments and contracts
3. Unrecovered regulatory assets
4. Nuclear decommissioning expenses.
CTC allows customers to take service from competitive suppliers who will provide commodity service over existing utility facilities in the deregulated state.
CTC will be reduced over time as the generation and power supply contracts are sold and the profit from these sales is passed on to the ratepayers.
Compressors: Machines designed for compressing air or gas from an initial intake pressure to a higher discharge pressure.
32. What is Compressed Air?
Air that has been pressed into a volume smaller than it normally occupies. As compressed air exerts pressure, it has stored potential energy.
The compressed air performs work when released and allowed to expand to its
33. What is Compressor Module?
Also referred to as an AIR Station Module, a "Compressor Module" is a complete, prefabricated compressor system.
The components of a complete Compressor Module are inlet filter, compressor, after cooler, prefilter, air dryer, after filter and associated subsystems.
The Compressor Module is prefabricated and delivered to the customer’s site. Several Modules are assembled together to create an AIR Station.
34. What is Compressor Station?
"Compressor Station" means the facility to be installed, owned and operated by Seller for the compression, drying, delivery and metering of Compressed Air. The CDA product is referred to as an AIR Station
35. What is Compressor Station Site?
"Compressor Station Site" means the plot of land or building to be furnished by the Buyer, subject to Seller's approval, for the Compressor Station.
The Compressor Station site, location and boundaries will be defined as part of the final contract execution.
36. What is Condensate?
The liquid that forms when compressed air is cooled, or when air is compressed at constant temperature.
The condensate produced by compressed air is water, although it may be contaminated with oil, dirt or other materials present in the incoming air.
37. What is Coriolis Force?
An apparent force used mathematically to describe motion, as of air, relative to a non inertial uniformly moving frame of reference.
38. What is Central Operation Management System (COMSYS)?
"COMSYS" is the group of systems that allow CDA to maintain a telepresence in the compressor system. Using COMSYS CDA can continuously monitor and control the Compressor Station.
39. What is CENTRY™ Control Panels?
The family of control panels developed and marketed by Clean Dry Air, Inc. The CENTRYPCS (Plant Control System) and CENTRYCLC (Compressor Level Controller) are used in the CDA AIR Stations.
40. What is Check Valve?
In an air system, a valve that permits air flow in one direction only.
41. What is Compressed Air Distributing System?
"Compressed Air Distributing System" means the system of trunk and service pipelines now or hereafter constructed, owned, or operated and maintained by Buyer and used to transport Compressed Air from the Compressor Station to the various use points within the facilities owned or operated by Buyer.
42. What is Dalton's Law?
States that the total pressure is equal to the sum of the partial pressures for a mixture of independent substances ( the constituent gases).
The partial pressure is the pressure each constituent gas would exert if it alone occupied the volume of the mixture.
43. What is Delivery Point of Compressor?
The "Delivery Point" is the connection between the Compressed Air Distributing System and the Compressor Station.
Each party shall supply a flange to mate with the other's connecting flange on all piping connections.
The locations of such flanges shall be considered the delivery point (the "Delivery Point"). Unless otherwise agreed to, it is the buyer’s responsibility to connect from the compressor station Delivery Point to their Compressed Air Distributing System.
44. What is Deliquescent Dryers?
A dryer which employs a chemical in the form of a tablet to absorb moisture. The chemical degrades into a liquid which is drained off periodically.
Similarly the dryer has to be 'topped up' with new tablets to continue working. Demand: The flow of air required to satisfy usage at specified temperature and pressure conditions.
45. What is Demand Controller?
Sometimes also called a "demand expander". We have to be politically correct when discussing these devices.
There are users of these devices that claim great reductions in energy costs. We just have not been able to understand the fluid dynamic principles that support the theory of operation.
We believe they may be successful in lowering the demand side pressure which in turn would cause the leaks to "leak less". Of course you always want to minimize the production side system pressure so there is still a disconnect.
This is a device that is placed within the air system. It is sold on the basis that they maintain constant system pressure.
We can see some benefit in applications where non-modulating (on-line/off-line control) compressors are applied.
Be careful if the device you are considering requires storage capacity that is maintained at pressures higher than actual system pressure or point of use requirements .
On a fundamental level this is inefficient. CDA neither recommends nor not recommends these devices.
46. What is Deregulation?
Deregulation splits off two lines of the power business that have been controlled by regulated monopoly utilities.
It allows new players to compete in providing electric services setting their own prices rather than negotiating with state regulators on a fixed rate.
47. What is Desiccant?
A substance such as calcium oxide or silica gel that has high affinity for water and it is used as a drying agent.
48. What is Diffuser?
An item within an aerodynamic compressor which converts the velocity head into a static head.
The diffuser usually consists of a set of vanes at specific angles so that the discharged air is efficiently slowed down.
49. What is Discharge Pressure?
The actual pressure that is available from the air compressor. This is not the same as the system pressure or the required pressure.
It is important to ensure that a new compressor has a discharge pressure which is great enough to overcome losses through pipes and any air treatment, so that it can meet the required system pressure.
50. What is Dryer?
A device designed to minimize water in compressed air systems. Several types are available, refrigerated, desiccant.
51. What is Electric Power Grid?
A complex infrastructure of electric power lines and substations that support the delivery of electricity generated by linked power plants.
52. What is Electronic Data Interchange (EDI)?
Electronic exchange of data for customer enrollment, billing data exchange, termination of service, etc.
53. Energy Savings Performance Contracting (ESPC)?
ESPC is a method of reducing energy use and costs at no capital cost to the company. Under an ESPC, an energy services company (ESCO) pays all costs involved in identifying, installing, operating and maintaining the energy-efficient equipment and improvements.
The ESCO is compensated by receiving a share of the cost savings resulting from these improvements. At the end of the contract (which can extend to 25 years) the company owns all the improvements and receives all of the continuing savings.
54. What is Fahrenheit ( °F)?
The international temperature scale where water freezes at 32 (degrees) and boils at 212 (degrees).
55. What is Federal Energy Regulatory Commission (FERC)?
The agency that monitors sales of electricity across state lines and regulates the use of transmission lines for such sales.
56. What is Firm Capacity Plant?
A "Firm Capacity" plant is one in which all the major components in the plant are backed up. For example, in a CDA Compressor Station that requires two modules to meet the contract requirement a complete third module would be installed to meet the classification of Firm.
A Firm Capacity plant requires significantly more capital investment on the part of CDA. The customer should specify a Firm Capacity plant when they cannot tolerate any reduction in the delivered compressed air capacity due to machine maintenance or failure.
57. What is Fouling?
Accumulation of foreign matter, such as mud or debris, in a cooler, pipe, or valve. In a cooler, H2O DP and DT will be seen to increase, as well as CTD (.H2O T in to Air T out)
58. What is Free Air Delivered (FAD)?
Air at normal atmospheric conditions. Be careful, since the altitude (barometer) and temperature vary at different localities and at different times, it follows that this term does not mean air under identical conditions.
It is much more desirable to define SCFM and specify the required capacity.
59. What is Gas and Mechanical Horsepower?
The total brake horsepower consumed by a compressor is made up of two components.
First, the gas horsepower which is only the power required to compress the air.
Second, the mechanical horsepower, which is the power consumed by compressor itself.
Mechanical horsepower is sometimes referred to as parasitic loss, it is the power consumed by the gear train or running gear.
60. What is Hot Start?
The compressor is started automatically, depending on demand. Control panel is energized with no "pre- start" cycle required, as pre-lubrication pump and buffer (seal) air are always "on".
A state of pre-start exists. Steam turbine compressors are "slow-rolling" to maintain "pre-start" turbine temperatures at an adequate, recommended level.
A higher level of instrumentation and monitoring accessories are recommended when Hot Starting.
61. What is Incremental Air Fee?
The "Incremental Air Fee" is the charge for compressed air consumed above the BAR and is charged based on the quantity consumed.
Incremental Air Requirement (IAR): The quantity of air required in excess of the Base Air Requirement. Air compressors are designed as frame sizes. Each frame size will deliver up to a certain amount of flow. Many times the air requirement of a customer will fall in the middle to bottom of a compressor frame.
This creates additional available capacity from the compressor or AIR Station. This additional capacity may not be utilize initially, but is available, usually at a reduced rate, to the customer in the future.
Incremental air capacity can be intentionally built into the AIR Station, but this usually results in additional capital cost which is reflected in the facility fee.
62. What is Independent System Operator (ISO)?
A regulatory body responsible for the operation and control of the statewide transmission grid.
ISO ensures efficient use and reliable operation of the transmission grid consistent with fulfillment of rigorous planning and operative reserve criteria.
ISO adopts inspection, maintenance, and repair and replacement standards of transmission facilities under its control as well as standards for safety and reliability during periods of emergency and disaster. It also participates in all relevant Federal Regulatory Commission proceedings.
63. What is Inlet Filter?
Specified and applied to assure that the air entering the compressor is free of foreign matter.
Many types of inlet filters are available. It is important to the long life of a compressor that the correct inlet filter is selected.
64. What is Intercoolers?
Heat exchangers for removing the heat of compression of the air or gas between consecutive stages of multistage compressors.
65. What is Interruptible Capacity Plant?
An "Interruptible Capacity" plant does not have an installed spare and can suffer decreases in delivered capacity.
An Interruptible Capacity plant is designed to accommodate rapid hookup of rental air compressors to minimize capacity reductions.
This type of plant requires a lower capital investment, which is reflected in a lower facility fee.
66. What is Investment Grade Site Survey?
Once a customer indicates their intent to enter into an air contract with CDA , we will conduct an investment grade site survey.
This is a detailed review of the station site and all aspects of installing and starting the air station.
The Survey may include soil samples and review of potential underground obstructions. During the Survey the various air station interfaces to the customer's plant will be defined.
67. What is Kelvin?
A unit of absolute temperature equal to 1/273 of the absolute temperature of the triple point of water.
In Kelvin, absolute zero (absence of heat) is - 273.16 °K.
68. What is Kilowatt Hour (kWh)?
Unit of measure equal to 1,000 watts used continuously for one hour.
69. What is Line Filter?
Installed in the compressed air line, line filters are designed to trap entrained foreign matter harmful to pneumatic tools, equipment and instrumentation.
70. What is Load Shape?
The variation in the magnitude of the power or compressed air load over a daily, weekly or annual period.
71. What is Mach Number?
The ratio of the actual velocity at a given point to the velocity of sound in the same gas at the conditions existing at this point.
These are known as local conditions.
72. What is Maximum Instantaneous Compressed Air Delivery Rate?
The Base Air Requirement plus the Incremental Air Requirement. This is the maximum capacity available from the AIR Station with all compressors running and fully loaded.
73. What is MAWP?
The Maximum Allowable Working Pressure. This data should be found on the pressure vessel nameplate.
It represents the maximum pressure at which the vessel may operate. The lowest set safety valve should be set at the MAWP.
74. What is Maximum Operating Pressure?
This is different than MAWP. This is the highest operating pressure the system or component is designed to withstand.
75. What are Moisture separators?
Devices for collecting and removing moisture precipitated from the air or gas during the process of cooling.
Moisture separators are designed to trap and expel, automatically or manually, any oil or condensed moisture which develops in a compressed air system.
76. What are Multi-stage Compressors?
It is also called compound compressors, they are those in which compression from initial to final pressure is completed in two or more distinct steps or stages.
N cu m/min (also N cu m/hr): Volume flow rate measured in normal cubic meters per minute (or hour), i.e. related back to normal inlet conditions.
77. What is NTP?
Normal Temperature and Pressure. This is based upon a temperature of 32 deg F (0 deg C) and a pressure of 1 bar.
78. What is Nozzle?
A projecting part with an opening, as at the end of a hose, for regulating and directing a flow of fluid.
79. What is Oil-free compressor?
The term generally applies to the condition of the air either when it leaves the compressor, or after filtration.
An oil-free compressor will have no lubrication on the compression side of the machine.
However this may not result in oil- free compressed air, simply due to the fact that the ambient air being sucked into the compressor will contain hydrocarbons which will condense into liquid oil further down stream.
80. What is Oil-less compressor?
A term applied to compressors that contain no oil. A small reciprocating compressor with PTFE piston rings and PTFE bearer rings, sealed for life bearings and no sump oil would be called an oil-less compressor.
81. What is Package Power?
The total power absorbed by a compressor, including the power absorbed by all pumps, fans, coolers and the like. This is the figure to look for when buying a compressor.
82. What is Pascal?
SI unit of pressure equal to one Newton per square meter. 1 Pa is a very small unit of pressure.
For this reason kPa (1000 Pascal's) is more often used. 1 psi = 6.8948 kPa.
83. What is Piston Displacement of a Compressor Cylinder?
The volume swept through by the piston. This is expressed as a rate, such as cubic feet per minute.
The piston displacement of a multi-stage reciprocating compressor is that of the first stage only, since the same gas passes through all stages in series.
84. What is Pneumatic working?
It is relating to air other gasses. Run by or using compressed air: a pneumatic drill. Fill with air, especially compressed air: a pneumatic tire.
85. What are Portable Compressors?
Used in the construction industry or as emergency compressed air backup, portables consist of a compressor and driver mounted that they may be readily moved as a unit.
86. What is Positive Displacement compressor?
This describes reciprocating, rotary lobe, rotary vane and screw type compressors.
This type of compressor does not 'stall' and potentially can reach pressures well in excess of the design pressure.
87. What is Pressure Dew Point?
In some sales leaflets this is referred to as PDP. The PDP is the temperature at which water will condense out of the pressurized compressed air.
Two components define pressure dew point, the dew point temperature at a specified line pressure.
88. Pressure Swing Dryer?
A desiccant dryer either heat less or heat reactivated.
89. What is PSIA?
Pounds per Square Inch Absolute.
This is the pressure of a system measured from absolute zero. It is exactly 1 atmosphere more than PSIG.
90. What is PSIG?
Pounds per Square Inch Gauge.
This is the pressure of a system which you would see displayed on a normal pressure gauge.
It is the pressure of the system, over and above atmospheric pressure.
91. What is Rankine?
A scale of absolute temperature using Fahrenheit degrees in which the freezing point of water is 491.69° R and the boiling point of water is 671.69° R.
92. What are Reciprocating Compressors?
Those in which each compressing element consists of a piston moving back and forth in a cylinder.
Classified as a positive displacement compressor. Single acting reciprocating compressors are those in which compression takes place on but one stroke per revolution in each compressing element.
Double acting compressors are those in which compression takes place on both strokes per revolution in each compressing element.
93. What is Receiver?
The vessel used to contain compressed air. As a general rule of thumb most systems need a minimum of a 'one minute receiver'.
Although wholly inaccurate, the following will provide the basis of most systems. 700 cfm
compressor at 7 barg. 700/7 = 100 cubic ft receiver. 700 cfm compressor at 10 barg. 700/10 = 70 cubic ft receiver.
94. What is Relative Humidity?
The ratio of the partial pressure of the water vapor to the saturation pressure at the air temperature.
95. What is Reynolds Number (Re)?
Represents the ratio of inertia to viscous force. At low Re the viscous effects dominate and the flow is laminar.
At high Re the inertial forces dominate leading to turbulent flow.
96. What are Safety Valves?
Pressure limiting devices used on all air receivers built to code. They limit pressure to the maximum working pressure allowable.
Safety valves are also installed in air lines between the compressor discharge and receiver when a equipment shut-off valve is present.
Don't take the operation of your safety valves for granted. Compressed air has and will kill! Have your system and safety valves inspected by a compressed air specialist.
97. What is Saturation?
The condition in which air at a specific temperature contains all the water vapor it can hold; 100% relative humidity.
Occurs when the vapor is at the dew point or saturation temperature corresponding to its partial pressure.
A gas in never saturated with a vapor. However, the space occupied jointly by the gas and vapor may be saturated.
98. What is Scaling?
Build-up of foreign matter on the interior (H2O) surface of coolers and pipe.
Often caused by the precipitating- out of calcium carbonates due to high temperatures at the "hot" end of a cooler.
With a cooler, seen as an increase of CTD (high air temperature) and lower temperature rise. Unfiltered, untreated, and oxygenated water are the most frequent causes in pipe.
99. What is Separator?
The term used to describe the filter inside an oil injected screw compressor which removes the hot oil from the hot compressed air.
The separator element is a consumable component which traps oil (and dirt) particles down to 1 micron.
This means that a separator element may last for years in a clean factory and only months in a dusty factory.
100. What is S.I.: System International?
The international system of unit measurement.
101. What is Site Survey?
Before CDA can finalize a Contract AIR™ proposal, a site survey must be completed.
A Site Survey Form is used to gather needed information on plant layout, the station site, etc.
The time required to complete the survey can be greatly reduced if the customer begins to gather the information prior to CDA arriving onsite.
102. What is Slippage?
This refers to the compressed air lost due to in-efficiency in the design of the compressor. In a reciprocating compressor, some of the air will seep back past the gaps in the piston rings.
In a screw compressor, some air will slip back through the small gaps which exist between the screw compressor rotors. This loss is called slippage.
103. What is Snifting Valve?
This is a safety relief valve which works backwards and is used in vacuum systems. Instead of venting compressed air out of the system like a normal safety relief valve, it lifts at a pre-set vacuum to allow air into the system thereby protecting the vacuum pump.
104. What is Specific Gravity?
The ratio of the mass of a solid or liquid to the mass of an equal volume of distilled water at 4° C (39 °F) or of a gas to an equal volume of air or hydrogen under prescribed conditions of temperature and pressure.
105. What is Specific Power Consumption?
A quick and easy way of comparing compressor efficiencies, as long as you have exactly the right information before you start.
The total package power is divided by the actual volume delivered at a specified pressure.
It is usually expressed as " X " HP per 100 cfm. Some people turn this figure around and quote X CFM per HP, or X Cu Meters/hour per kW.
106. What is Stack Up?
The interaction between the stages of a centrifugal compressor. When a multi-stage compressor is designed, each stage can operate at only one point its characteristic curve. The point is determine by the design conditions of temperature, flow and pressure.
As the design conditions change the point on the stage characteristic curve will shift. The interaction of each stage curve is referred to as the "stack up" of the compressor.
107. What is Stall in Centrifugal pump?
In a centrifugal compressor stage stall is mild form of surge. It is the flow at which the stage is no longer making any ratio, but has not surged.
The flow actually becomes detached from the tips of the impeller rendering it ineffective.
Stall can be heard as a rumbling in the discharge pipe. Running for extended periods of time in stall can cause a impeller blade failure due to vibration and fatigue.
108. What is Static Head?
This is indicated by a pressure gauge on a pipe or system. It is not necessarily the total pressure of the system, particularly if the velocities are high. See velocity head.
109. What is Stonewall?
Sometimes called choke, it the point at the opposite end of the centrifugal characteristic from the natural surge point.
Stonewall is the maximum flow that can be passed through a centrifugal compressor impeller.
Swept Volume: Watch out for this one! This term is mainly used by companies selling small compressors because it
makes their compressors look bigger than they really are. The swept volume is the actual displacement of the piston,
forgetting such losses as bumping clearances, valve clearances, ring losses and the like. If a compressor is rated for a
delivery of 15 cfm, swept, be prepared to actually get about 10 Scfm delivered.
Telepresence: Being there without being there. The main idea of ubiquitous telepresence (UT) is to allow CDA experts
to project their physical presence anywhere on the Internet. Specifically, CDA experts are given the ability to explore
and interact with many remote systems (e.g., all sites on COMSYS) through remote sensing and observation devices.
Torr: A unit of pressure used with vacuum pumps, equal to 1mm of mercury and 133.32 Pascal's.
Turbine: A rotary engine that converts the energy of a moving stream of water, steam, or gas into mechanical energy.
The basic element in a turbine is a wheel or rotor with paddles, propellers, blades, or buckets arranged on its
circumference in such a fashion that the moving fluid exerts a tangential force that turns the wheel and imparts energy
to it. This mechanical energy is then transferred through a drive shaft to operate a machine, compressor, electric
generator, or propeller. Turbines are classified as hydraulic, or water, turbines, steam turbines, or gas turbines. Today
turbine-powered generators produce most of the world's electrical energy. Windmills that generate electricity are known
as wind turbines
Vacuum Pumps: Machines for compressing air or gas from an initial pressure which is below atmospheric to a final
pressure which is near atmospheric. Absolute vacuum is a theoretical void in which no particles exist. However, even
outer space contains pressure, 10**(-19) torr. A vacuum pump is a machine which sucks in air from a closed or
restricted space. The harder it works, the closer it gets to absolute vacuum. The air delivered from a vacuum pump is
called 'aspired air'.
Velocity Head: This is best explained by analogy, imagine a fireman's hose. The pumps are delivering water through
the hose at 100 psig, however you can easily cup your hands around the water jet. Stand in front of the jet and you end
up on your back. The pressure from the hose is almost entirely velocity pressure which is the same as velocity head. Venturi: A short tube with a constricted throat used to determine fluid pressures and velocities by measurement of
differential pressures generated at the throat as a fluid traverses the tube.
Volumetric Efficiency: In positive displacement compressors it is the ratio of the actual capacity of the compressor to
displacement and is expressed in per cent.
Vortex: A spiral motion of fluid within a limited area, especially a whirling mass of water or air that sucks everything
near it towards its center.
Wet Bulb Temperature: Is used in psychrometrics and is the temperature recorded by a thermometer whose bulb has
been covered with a wetted wick. A sling psychrometer has both a wet and a dry bulb thermometer mounted on a
common swing handle. The psychrometer is whirled around, providing the necessary air flow over the wet bulb. The wet
and dry bulb readings permit the determination of relative humidity of the atmosphere. Some psychrometric calculations
can be performed using the psychrometric calculator.
Newton’s Law
Newton’s first law states a body at rest will remain at rest, or a body in motion will continue in straight-line motion unless
subjected to an external applied force. That means, if one sees a bend in the flow of air, or if air originally at rest is
accelerated into motion, there is a force acting on it. Newton’s third law states that for every action there is an equal and
opposite reaction.
Newton’s second law that relates the acceleration of an object to its mass and to the force on it; F=ma)
What is the surface finish of seal faces?
Silicon / tungsten carbide 0.05 micrometers C.L.A
Alumina ceramic 0.30 micrometers C.L.A
Satellite or other metals 0.12 micrometers C.L.A
Carbon 0.25 micrometers CL.A
What is the flatness of seal faces?
Up to 75mm diameter 2 light bands (0.0006 mm)
Over 75 mm diameter 3 light bands (0.0009 mm)
What are the recommended tolerances for a mechanical seal?
Shaft diameter in seal area : nominal size +0.00/-0.05 mm
Shaft finish in seal area : 0.8 micrometers C.L.A
Shaft end play : 0.1 maximum
Shaft run out in seal area:
Size 25 mm 50 mm 75 mm 100 mm
Tolerance 0.03 0.05 0.08 0.10
(Full indicator movement)
Square ness of shaft to stuffing box face:
Size 25 mm 50 mm 75 mm 100 mm
Tolerance 0.05 0.05 0.08 0.10
(Full indicator movement)
Concentricity of sleeve and box bore:
Size 25 mm 50 mm 75 mm 100 mm
Tolerance 0.05 0.08 0.1 0.13
(Full indicator movement)