Question

A pump is required to deliver 100 gpm at a head of 100 ft, but the pump rated capacity is 150 gpm at a head of 100 ft. If the pump speed is constant, what will be the effect of valving the pump discharge to reduce flow?

(A)

The system curve will shift downwards, and the pump efficiency will decrease.

(B)

The system curve will shift downwards, and the pump efficiency will increase.

(C)

The system curve will shift upwards, and the pump efficiency will decrease.

(D)

The system curve will shift upwards, and the pump efficiency will increase.

Answer 1

System curve is a graphical representation of discharge and head loss in a pipe system

This curve doesn't depend on pump characteristics

This curve is parabola as H depend on velocity square which means discharge square

As dicharge is reduced so curve shift upward as head is same so we discharge is reduced then curve shift upward to maintain same head

And
Efficiency of pump is directly proportional to discharge

If discharge is reduced then accordingly efficiency of pump reduce

Hence, option C is correct