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

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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 ______
a) Adiabatic expansion
b) Isentropic compression
c) Adiabatic compression
d) Isentropic expansion
View Answer

Answer: b
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
View Answer

Answer: d
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
View Answer

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

Answer: b
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
View Answer

Answer: d
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.

6. Formation of bubbles in an impeller is called ______
a) Cavities
b) Defects
c) Friction
d) Heat burn
View Answer

Answer: a
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
View Answer

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

Answer: b
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
View Answer

Answer: d
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.
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10. Wear of impeller can be worsened by __________
a) Draft tube
b) Pump pressure
c) Suspended solenoids
d) Turbine head
View Answer

Answer: c
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
View Answer

Answer: b
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
View Answer

Answer: b
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
View Answer

Answer: a
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
View Answer

Answer: c
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
View Answer

Answer: a
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.

Sanfoundry Global Education & Learning Series – Hydraulic Machines.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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