Laws of affinity

The laws of affinity express the mathematical relationship between flow, pump speed (rpm), head and power consumption for centrifugal pumps.

The laws of affinity express the mathematical relationship between flow, pump speed (rpm), head and power consumption for centrifugal pumps. The laws shows that even a small flow reduction will result in significant power reductions and hence energy consumption. The laws are the foundation of energy savings.

When one of the variables involved in pump performance is changed the other variables can be calculated by means of the law of affinity.

Q1/Q2 = n1/n2
H1/H2 = (n1/n2)2
P1/P2 = (n1/n2)3

Q = flow [m3/h]
n = pump speed [rpm]
H = head [bar]
P = power [kW]

The formulas show that if the pump speed is reduced by 50%, the flow will be reduced to 50% as well. The head will be reduced to 25%, and power consumption will be reduced to 12.5%.





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