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Pumps | Interview Questions Blog Contains 


1. Why centrifugal pumps are widely used in process industries than positive displacement pumps?
2. When to use gear pumps?
3. When we need pumps in parallel and pumps in series?
4. What is priming in centrifugal pumps?
5. When do you use gear pump?
6. Comparing reciprocating & centrifugal pump
7. What is difference between Pump head & Discharge Pressure? How to convert Discharge pressure into Head?

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1. Why centrifugal pumps are widely used in process industries than positive displacement pumps?

Centrifugal pumps ate widely used in process industries. Because
1) 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. 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
Reciprocating pump

simple in construction



Complicated in construction



Requires less floor are
Requires more floor area

Suitable for large discharge
Suitable for small discharge

can handle dirty water
Cannot handle dirty water

Continuous delivery
Pulsating delivery

Need priming
Does not need priming

Less efficiency
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
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Thanks for reading - Pumps | Interview Questions
Naitik Patel
Industrial Guide

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