# Hydraulic Machines Questions and Answers – Multistage Centrifugal Pumps for High Discharge

This set of Hydraulic Machines Multiple Choice Questions & Answers focuses on “Multistage Centrifugal Pumps for High Discharge”.

1. The mechanical energy can be measured by ______
b) Isentropic compression
d) Isentropic expansion

Explanation: The mechanical energy in a centrifugal pump that is driven by the impeller mounted on a shaft is measured by isentropic compression. Thus, the correct choice is isentropic compression.

2. How many impellers does a multistage centrifugal pump have?
a) Zero
b) One
c) Exactly two
d) Two and more

Explanation: The centrifugal pump consists of two or more impellers. The impeller is mounted on one shaft or different shaft. A multistage centrifugal pump has more than two impellers. The multistage centrifugal is similar to the centrifugal pumps working.

3. The energy usage in pumping installation is determined by _______
a) Friction characteristics
b) Pipe diameter
c) Surface tension
d) Thermal expansion

Explanation: At each stage in the centrifugal pump, the fluid is directed to towards the centre. The energy usage in pumping installation is determined by Friction characteristics. Thus, it is the most suitable option.

4. Which among the following is a friction factor?
a) Newtons factor
b) Darcy’s factor
c) Transfer temperature
d) Heizenberg’s factor

Explanation: From the above, the factor that involves friction is determined by Darcy’s friction factor. The energy usage in pumping installation is determined by Friction characteristics. Thus, it is used in energy calculations in a pump.

5. What is the dimension for Darcy’s friction factor?
a) kg/m
b) N/mm
c) kg
d) Dimensionless

Explanation: Darcy’s friction factor is dimensionless. It is one of the major applications in Fluid dynamics. The energy usage in pumping installation is determined by Friction characteristics. Thus, it is dimensionless.
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6. Formation of bubbles in an impeller is called ______
a) Cavities
b) Defects
c) Friction
d) Heat burn

Explanation: Formation of bubbles in an impeller is called as its as its cavities. These cavities develop intense shockwaves in the impeller.

7. Centrifugal pump works by imparting _______
a) Potential energy
b) Kinetic energy
c) Heat energy
d) Electrical energy

Explanation: Centrifugal pump works by imparting kinetic energy to the liquid for rotating the impeller rotor.

8. What is the full form of NPSH in a pump?
a) Net pressure suction head
b) Net positive suction head
c) Non-pressure suction head
d) Net pressure super head

Explanation: The full form of NPSH is Net positive suction head. The head added by the pump is a sum of static lift. Thus, corresponds to the efficient working of the pump. Higher the NPSH, more efficient the pump is.

9. When the NPSH is low, it leads to ________
a) Breaking
b) Wear
c) Corrosion
d) Cavitation

Explanation: When the NPSH is low, it leads to cavitation. Cavitation is one of the major drawbacks that are seen in a centrifugal pump. There are various other problems as well. But, cavitation is due to low NPSH.

10. Wear of impeller can be worsened by __________
a) Draft tube
b) Pump pressure
c) Suspended solenoids

Explanation: Wear of impeller can be worsened by suspended solenoids. Wear and tear is one of the major drawbacks that are seen in a centrifugal pump. It affects the working of the impeller, thus resulting in an inefficient working.

11. Which pump is the most efficient centrifugal pump?
a) Electrical pump
b) Reciprocating pump
c) Heat pump
d) Pressure pump

Explanation: Reciprocating pump is the most efficient centrifugal pump because as the pressure increases, the flow rate remains constant.

12. Corrosion in the pump is developed due to _______
a) Pressure of air
b) Fluid properties
c) Draft tube
d) Tank dimensions

Explanation: Corrosion in the pump is developed due to fluid properties. The flow of fluid plays a major role in determining the corrosion developed. Fluid flow can broadly be classified into laminar and turbulent depending on its Reynolds number.

13. Over heating is a major problem faced in a pump.
a) True
b) False

Explanation: Over heating is a major problem faced in a pump. The temperature in a centrifugal pump is increases mainly due to the presence of low flow. Thus, by heating the fluid, the velocity of fluid flow increases.

14. What is the effect of cavitation in boat propeller?
a) It recirculates air
b) The pressurizes the air
c) It leads to fast spinning
d) It breaks the bubbles

Explanation: Cavitation in a boat propeller or a ship propeller leads to fast spinning due to the formation of bubbles.

15. Lack of prime is a problem faced in centrifugal pump.
a) True
b) False

Explanation: Yes, Lack of prime is a problem faced in centrifugal pump. It means that the centrifugal pump must be filled in order to operate in an effective way. The fluid must be filled in such a way so that it can pump.

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