Understanding a Pump Performance Curve

A curve relates flow and head at a specified speed and configuration. The operating point depends on pump performance and system requirements. Maximum flow and head are usually different points. Review power, efficiency and NPSH where approved data is available.

The pump curve

The horizontal axis shows flow and the vertical axis shows head. As flow increases, the head the pump can develop falls. The highest head is reached at low flow; the highest flow is reached at low head. A curve is valid only for the speed, impeller diameter and fluid basis stated on it.

The system curve

Your pipework has its own curve: the static lift is present even at zero flow, and friction losses rise as flow increases. The duty point is where the pump curve and the system curve cross. Changing the hose diameter, the pipe length or the discharge level moves the system curve, and therefore the duty point.

Other values on a curve

• Power: the power the pump needs at each flow, used to check the engine or motor.
• Efficiency: how much of that power becomes useful hydraulic work.
• NPSH required: the suction conditions the pump needs to avoid cavitation, compared with the NPSH available on site.

SmartCo publishes curves only from original manufacturer data for approved models. Where a curve is not yet published, request the datasheet for the model you are considering.