Pump Power & Efficiency

Correctly calculating a pump system’s power requirement is necessary both for correct motor selection and for estimating operating costs. Power is calculated across an increasing three-stage chain:

1. Hydraulic power (Ph): the useful power actually transferred to the fluid — calculated with the formula ρgQH.
2. Shaft power (Ps): the power that must be applied to the shaft to compensate for the pump’s mechanical inefficiencies (seal losses, hydraulic losses) — Ps = Ph/ηpump.
3. Electrical power (Pe): the total power drawn from the grid, also accounting for the motor’s own inefficiency — Pe = Ps/ηmotor.

Important note about head (H): this value must include not just the static height difference, but also all friction losses (hL) in the pipeline. For a correct pump selection, the head loss calculated with the Pipe Pressure Loss tool must be added to the static height.

For motor power selection, a typical 10% safety margin is added on top of the calculated requirement, then rounded up to the nearest standard motor power.