Pump Basics: Affinity Laws

Law 1- Speed is directly proportional to Flow.

Law 1 means that as RPM is reduced, flow (GPM) is reduced in a linear relationship. For example, if RPM drops to 70% of the original, GPM drops to 70% of the original.

Law 2 – Head is proportional to Flow squared.

Law 2 means that as RPM is reduced, pressure (feet of head) is reduced by the square. For example, if RPM drops to 70% of the original, feet of head would drop by (70% x 70%) = 0.72 = 0.49 or 49% of the original.

Law 2 – Input power is proportional to Flow cubed.

Law 3 means that as RPM is reduced, power consumption (brake horsepower) is reduced by the cube. In the same example the power would drop to (0.7 x 0.7 x 0.7) = (0.7)3 = 0.343 or 34.3% of the original.