September 23, 2020

Fundamental Pump Laws

By Mac MacCormack

Fund. pump feat. image

It doesn’t matter what size, shape or design of the pump its purpose is to move fluids. Head loss that must be overcome makes the task a bit more complicated and the type of pump makes a difference.

Two of the basic pump laws are volumetric flow rate and pump power:


Volumetric Flow Rate:

The capacity of a centrifugal pump is directly proportional to its speed.

Expressed mathematically:

V @ N whereas; V = Volumetric flow rate and N = Speed

If  pump speed is doubled, pump capacity will double. If cut 50%, capacity will be halved. Discharge head is directly proportional to the square of pump speed.

Expressed mathematically:

Hp @ N2

If a pump’s speed is doubled, its discharge head will go up by a factor of four.


Pump Power:

Power required  by the pump’s driver is directly proportional to the cube of the pump speed.

Expressed mathematically:

P @ Nwhereas: P = Power required and N = Speed

If the pump’s speed is doubled, the power required by its driver will go up by a power of 8!


Why is this important? I will discuss this in a future blog about troubleshooting centrifugal pumps.