This set of Hydraulic Machines Questions and Answers for Campus interviews focuses on “Net Positive Suction Head – NPSH”.
1. In hydraulic head, NPSH is used for the analysis of __________
a) Adiabatic expansion
b) Priming
c) Wear
d) Cavitation
View Answer
Explanation: In hydraulic head, net positive circuit is used for the analysis of cavitation. It determines the cavitation present in the centrifugal pump by different methods.
2. NPSH is the difference between _______
a) Suction pressure and vapour pressure
b) Vapour pressure and suction pressure
c) Suction pressure and heat
d) Shaft and head
View Answer
Explanation: NPSH is defined as the difference suction pressure and vapour pressure. It is called as the net positive suction head.
3. What can NPSH be used to determine _______
a) Friction characteristics
b) Pipe diameter
c) Cavitation
d) Thermal expansion
View Answer
Explanation: NPSH is used to determine the cavitation in pumps. NPSH is defined as the difference suction pressure and vapour pressure. It is called as the net positive suction head.
4. The measure of how close the fluid is to the given point is called _________
a) Flashing
b) Darcy’s factor
c) Transfer temperature
d) Heizenberg’s factor
View Answer
Explanation: The measure of how close the fluid is to the given point is called flashing. It is one of the major methods in the NPSH to determine the cavitation.
5. What is the dimension for Darcy’s friction factor?
a) kg/m
b) N/mm
c) kg
d) Dimensionless
View Answer
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. NPSH is relevant ________
a) Outside the pumps
b) Inside the pumps
c) Away from the pumps
d) Series and parallel with the pumps
View Answer
Explanation: NPSH is relevant inside the pumps. hydraulic head, net positive circuit is used for the analysis of cavitation. It determines the cavitation present in the centrifugal pump by different methods.
7. With the increase in cavitation, the drag coefficient of the impeller ______
a) Increases
b) Decreases
c) Same
d) Independent
View Answer
Explanation: With the increase in cavitation, the drag coefficient of the impeller increases. When the flow output is higher, impellers are connected in parallel. The impeller is mounted on one shaft or different shaft.
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
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
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. What is positive suction head?
a) Draft tube is above
b) Pump pressure is above
c) Liquid level is above
d) Turbine head is above
View Answer
Explanation: Positive suction head is defined as the point in which the liquid level is above the centre line of the pump.
11. NPSHr is determined by using ______
a) Pump pressure
b) PumpLinx
c) Heat transfer
d) Chemical energy
View Answer
Explanation: NPSHr of a pump can be determined by using Pumplinx. The full form of NPSH is Net positive suction head. The head added by the pump is a sum of static lift.
12. Corrosion in the pump is developed due to _______
a) Pressure of air
b) Fluid properties
c) Draft tube
d) Tank dimensions
View Answer
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. Calculation of NPSH in a turbine is different from the calculation of NPSH in a pump.
a) True
b) False
View Answer
Explanation: Calculation of NPSH in a turbine is different from the calculation of NPSH in a pump. It is mainly because the point at which the cavitation will first occur is in a different place.
14. If we use two lower capacity pumps in parallel, cavitation ________
a) Increases
b) Decreases
c) Same
d) Independent
View Answer
Explanation: If we use two lower capacity pumps in parallel, cavitation decreases. It happens when the NPSh value is bought in its safety limit.
15. Vapour pressure is strongly dependent on temperature in a pump.
a) True
b) False
View Answer
Explanation: Yes, Vapour pressure is strongly dependent on temperature in a pump. It will thus increase the net positive suction head of the centrifugal pump.
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