Concept reference

The Pump Curve

C.1Plain-language definition

A pump curve is the machine’s answer to a range of imposed flows. For a typical centrifugal pump, developed head falls as flow rises. Efficiency, absorbed power and NPSH required add other constraints, so the useful object is a family of aligned curves—not a single head-flow line.

C.2Governing relation or decision logic

Hydraulic power is Ph = ρgQH in W; pump input power is Pin = ρgQH/ηp. Read Q, H, efficiency, input power and NPSHr at the same operating point and speed. A trimmed impeller or changed speed creates a different curve.

C.3The failure to name

A catalogue curve is not proof of guaranteed performance unless its test standard, tolerances and supplied configuration are identified. Reading efficiency at the duty flow but head from a neighbouring diameter curve creates a fictitious pump.

C.4Field review checklist

• Confirm model, impeller diameter, speed, fluid basis and test/guarantee information.
• Use one vertical line to read all performance quantities at the operating flow.
• Mark preferred/allowable operating regions and end-of-curve limits supplied by the manufacturer.
• Check motor load and NPSH across the full system envelope, not only rated duty.

C.5Where it fits in the course

§6.1 teaches curve anatomy; §6.2 adds efficiency and power.