### Pump Laws

It is often necessary to determine how a pump will operate under differing operating conditions. The operating conditions of a pump that can most readily be changed are the impeller diameter and the rotational speed of the pump. In order to predict how the pump will behave prior to changing the speed or the impeller diameter.

The first affinity law is that the flow rate (Q) is directly proportional to the size of the diameter of the pump impeller (D) and/or the rotational speed (N) of the pump.

The second affinity law is that the total head (H) is directly proportional to the square of the size of the diameter of the pump impeller (D) and/or the square of the rotational speed (N) of the pump.

The third affinity law is that the power (P) is directly proportional to the cube of the size of the diameter of the pump impeller (D) and/or the cube of the rotational speed (N) of the pump.