How to determine the power of centrifugal pump prime mover

1, first using the following formula to calculate the pump shaft power

Where: Q - pump rated flow, m3 / h;
H - pump rated head, m;
r - medium weight;
η - efficiency of the pump rated conditions,%;
Pa - pump rated conditions of shaft power, kW.
2, select the appropriate safety factor K, to calculate the prime mover is equipped with power P
P = K·Pa P = K · Pa
When Pa ≤ 15kW time, K = 1.25;
When 15kW
When Pa> 55kW time, K = 1.1
3, the reference specifications of the original motivations to select the right mover.