Pumps | Interview Questions Blog Contains
1. Why centrifugal pumps are widely used in
process industries than positive displacement pumps?
Centrifugal pumps ate widely used
in process industries. Because1) They are simple to construct and operate
2) Installation and maintenance are easy
3) Casing can be made of up variety of materials
4) Noise free operation
5) No need of safety valve at discharge side in case of single stage centrifugal pumps
6) Can handle variety of liquids. The impeller MOC can be altered accordingly.
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2. When to use gear pumps?
When we need to handle high
viscous liquids we need gear pumps as they deliver a higher discharge pressure
(even up to 200 bars) than centrifugal pumps. They are used to pump
paints, resins, adhesives, pitch. diesel, crude oil etc. They are positive displacement
pumps.
3. When we need pumps in parallel and pumps in series?
If we need a higher discharge
flow (Q) we have to go for pumps in parallel arrangement. If we need a higher
head (H) we need to go for pumps in series
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4. What is priming in centrifugal pumps?
Priming is a technique used to
drive away the air entrapped in the suction line of a centrifugal pump.
3. When we need pumps in parallel and pumps in series?
If we need a higher discharge
flow (Q) we have to go for pumps in parallel arrangement. If we need a higher
head (H) we need to go for pumps in series[ads id="ads1"]
4. What is priming in centrifugal pumps?
Priming is a technique used to
drive away the air entrapped in the suction line of a centrifugal pump. If the
air present in the suction line are not removed the pump won’t be able to suck
the liquid from the reservoir as air is lighter medium whereas liquid is
heavier medium.
So the whole suction line and the part of casing is filled with water and the air is removed via the air vent. Also if air is allowed to enter to the impeller they will damage the impeller by flashing (cavitation).
Normally cavitation won’t occur in pump which is continuously in service as there is a little chance for the air to get into the suction line.
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5. When do you use
gear pump?
The gear pump is commonly used in the
chemical industry for handling high viscosity liquids including molasses,
paints, and greases.
6. Comparing
reciprocating & centrifugal pump
Centrifugal pump
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Reciprocating pump
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simple in construction
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Complicated in construction
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Requires less floor are
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Requires more floor area
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Suitable for large discharge
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Suitable for small discharge
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can handle dirty water
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Cannot handle dirty water
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Continuous delivery
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Pulsating delivery
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Need priming
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Does not need priming
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Less efficiency
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High efficiency
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7. What is difference between Pump head & Discharge Pressure? How to convert Discharge pressure into Head?
Head
Pump head is an elevation up to where Fluid will be lifted. It is length from Impeller eye to Fluid destination.Head's Unit is Meter
Discharge Pressure
- Centrifugal Pump generating Discharge pressure by creating centrifugal force.
- Discharge Pressure's Unit is Kg/cm2.
- Conversation of Pressure to Head
P = 0.1 * Head * Specific Gravity
8: What is Positive displacement pump? Name different types Positive displacement pump?
Positive displacement pump are those which discharge specific amount & quantity is constant.
Positive displacement pumps are that which prevents undesirable flow and pumps the fluid within the closed space.
Positive displacement pumps example are: Multistage pumps, Process type pumps, Chemical process pumps, canned motor pumps, Centrifugal pumps, Paper stroke pumps and deep well turbine pumps.