The Laws of Affinity are mathematical expressions that define changes in the capacity of the pump, load, and BHP when changes occur in the speed of the pump, in the diameter of the impeller, or both.
According to the laws of affinity:
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. The flow, Q, varies in direct proportion to the ratio of the diameter of the rotor, D, or the ratio of revolutions N:
- . The manometric height, H, varies in direct proportion to the square of the ratio of diameters of the rotor, D, or the square of the ratio of revolutions N:
- . The power varies in direct proportion to the cube of the ratio of diameters of the rotor, or the cube of the ratio of revolutions:
Subscript 1 refers to the initial condition and 2 to the new condition.
Note: The Laws of Affinity are only valid under conditions of constant efficiency.
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