The power required to drive a centrifugal pump is usually known as the brake horsepower. It can be expressed in terms of the water horsepower divided by efficiency.
In the metric system kilowatts (kW) are used. Due to hydraulic, mechanical and volumetric losses in a pump the actual or water horsepower available for work on the fluid is less than the total horsepower supplied.
Pump efficiency is the ratio of the water horsepower delivered by the pump and the brake horsepower delivered to the pump shaft. When selecting a pump, a key concern is optimizingpumping efficiency. The energy usage in a pumping installation is determined by the flow required, the height lifted and the length and friction characteristics of the pipeline. The power required to drive a pump is defined simply using SI units by:
- P is the input power required (W)
- BHP is the brake horsepower
- ρ is the fluid density (kg/m3 )
- g is the standard acceleration of gravity (9.81 m/s2 )
- H is the net pump head added to the flow (m)
- Q is the flow rate (m3 /s)
- η is the efficiency of the pump