Water hydraulics
Pump hydraulic and input power
- where
- hydraulic power (W)
- fluid density (kg/m³)
- gravitational acceleration (m/s²)
- volume flow (m³/s; any unit you pick is converted)
- pump differential head (m)
- input power (W)
- overall pump and motor efficiency (fraction; any unit you pick is converted)
Explain this equation
Works out the power a pump puts into the water, and the electrical power it is likely to draw. Use it to estimate pump energy at a duty point.
ρ × g × h is the pressure the pump adds, written as head. q is the volume flow. P_hyd is the useful hydraulic power. η is the overall pump and motor efficiency.
Power is pressure times volume flow. Dividing by efficiency gives the input needed, since some power is lost as heat and friction.
Sense check: 12 L/min at 5 m head is about 10 W hydraulic. At 40% efficiency that is around 25 W input, typical of a domestic circulator. Double the head or the flow and the power doubles.
Watch out: efficiency changes along the pump curve. Check the actual duty point and minimum flow.
Enter your values to see the result.
Good to know
Efficiency varies with duty point. Verify pump curve and minimum flow.
Sources
Results are arithmetic only. Worked examples are not recommended design settings. This library does not provide automatic gas pipe selection, live gas tightness tests, purging procedures, combustion acceptance limits, installation approval or commissioning certification. Manufacturer data and the applicable current method remain essential.