Affinity Laws for the Discflo Pump

There are four key variables in pump performance: capacity; head; power; and pump speed. The relationship between them can be expressed by the following equations, known as the affinity laws. Use these equations when the operating points you require are not shown on the curves.

In these equations,
Q = capacity (in GPM or m3/h)
H = total head (in ft or m)
BHP = brake horsepower (in HP or kW)
N = pump speed (in RPM)
D = Discpac diameter (in inches or mm)

For the same Discpac diameter, D:

For the same pump speed, N:

These equations can be used to estimate the pump's performance in terms of capacity, total head or power at a new Discpac diameter or pump speed, when the current performance is known.

Note: The affinity laws apply to the disc pump for the full range of capacity and head values, but for only a limited range of horsepower values, ±100 RPM from the existing value.