HYDRAULIC MACHINES INTERVIEW QUESTIONS AND ANSWERS :­

1. Reciprocating pumps are no more to be seen in industrial
applications (in comparison to centrifugal pumps) because of 
(a) high initial and maintenance cost 
(b) lower discharge 
(c) lower speed of operation 
(d) necessity of air vessel 
(e) all of the above. 
Ans: a

2. In a centrifugal pump casing, the flow of water leaving the
impeller, is 
(a) rectilinear flow 
(b) radial flow 
(c) free vortex motion 
(d) forced vortex 
(e) none of the above. 
Ans: c

3. Head developed by a centrifugal pump depends on 
(a) impeller diameter 
(b) speed 
(c) fluid density 
(d) type of casing 
(e) (a) and (b) above. 
Ans: e

4. For starting an axial flow pump, its delivery valve should be 
(a) closed 
(b) open 
(c) depends on starting condition and flow desired 
(d) could be either open or closed 
(e) partly open and partly closed. 
Ans: b

5. The efficiency of a centrifugal pump is maximum when its
blades are 
(a) straight 
(b) bent forward 
(c) bent backward 
(d) bent forward first and then backward 
(e) bent backward first and then forward. 
Ans: c

6. In a centrifugal pump casing, the flow of water leaving the 
(a) radial 
(b) radial 
(c) centrifugal
(d) rectilinear 
(e) vortex. 
Ans: e

7. Centrifugal pump is started with its delivery valve 
(a) kept fully closed 
(b) kept fully open 
(c) irrespective of any position 
(d) kept 50% open 
(e) none of the above. 
Ans: a

8. Axial flow pump is started with its delivery valve 
(a) kept fully closed 
(b) kept fully open 
(c) irrespective of any position 
(d) kept 50% open 
(e) none of the above. 
Ans: b

9. When a piping system is made up primarily of vertical lift
and very little pipe friction, the pump characteristics should
be 
(a) horizontal 
(b) nearly horizontal 
(c) steep 
(d) first rise and then fall 
(e) none of the above. 
Ans: c

10. One horsepower is equal to 
(a) 102 watts 
(b) 75 watts 
(c) 550 watts 
(d) 735 watts 
(e) 33000 watts. 
Ans: d

11. Multistage centrifugal pumps are used to obtain 
(a) high discharge 
(b) high head 
(c) pumping of viscous fluids 
(d) high head and high discharge 
(e) high efficiency. 
Ans: b

12. When a piping system is made up primarily of friction
head and very little of vertical lift, then pump characteristics
should be 
(a) horizontal 
(b) nearly horizontal 
(c) steep 
(d) first rise and then fall 
(e) none of the above. 
Ans: b

13. In a single casing, multistage pump running at constant
speed, the capacity rating is to be slightly lowered. It can be
done by 
(a) designing new impeller 
(b) trimming the impeller size to the required size by
machining 
(c) not possible 
(d) some other alterations in the impeller 
(e) none of the above. 
Ans: b

14. If a pump is handling water and is discharging a certain
flow Q at a constant total dynamic head requiring a definite
B.H.P., the same pump when handling a liquid of specific
gravity 0.75 and viscosity nearly same as of water would
discharge 
(a) same quantity of liquid 
(b) 0.75 Q 
(c) Q/0.75 
(d) 1.5 Q 
(e) none of the above. 
Ans: a

15. The horse power required in above case will be 
(a) same 
(b) 0.75 B.H.P.
(c) B.H.P./0.75 
(d) 1.5 B.H.P. 
(e) none of the above. 
Ans: b

16. Low specific speed of a pump implies it is 
(a) centrifugal pump 
(b) mixed flow pump 
(c) axial flow pump 
(d) any one of the above 
(e) none of the above. 
Ans: a

17. The optimum value of vane exit angle for a centrifugal
pump impeller is 
(a) 10­15° 
(b) 20­25° 
(c) 30­40° 
(d) 50­60° 
(e) 80­90°. 
Ans: b

18. In a centrifugal pump, the liquid enters the pump 
(a) at the top 
(b) at the bottom 
(c) at the center 
(d) from sides 
(e) none of the above. 
Ans: c

19. For small discharge at high pressure, following pump is
preferred 
(a) centrifugal 
(b) axial flow 
(c) mixed flow 
(d) propeller 
(e) reciprocating. 
Ans: e

20. In centrifugal pumps, maximum efficiency is obtained
when the blades are 
(a) straight 
(b) bent forward 
(c) bent backward 
(d) radial 
(e) given aerofoil section. 
Ans: c