How to Read a Pump Curve and Find Your Duty Point
Flow on one axis, head on the other — and four lines that decide whether your pump runs efficiently or destroys itself. A practical walkthrough.
Every centrifugal pump we build is tested against a performance curve before dispatch. That single chart tells you almost everything about how the pump will behave in your plant — if you know how to read it.
The axes
The horizontal axis is flow (m³/hr or LPM). The vertical axis is head (metres) — the pressure the pump develops, expressed as a column of liquid. The falling curve from left to right is the head-capacity curve: as flow increases, the head the pump can produce decreases.
Your duty point
Your plant presents the pump with a system curve — static lift plus friction losses, which rise with the square of flow. Where your system curve crosses the pump curve is the duty point: the flow and head the pump will actually deliver. You do not choose the duty point by picking a pump; the intersection chooses it for you. This is why 'give me a 5 HP pump' is not a specification — flow, head and liquid are.
Best Efficiency Point
Somewhere near the middle of the curve sits the Best Efficiency Point (BEP), where the pump converts the most shaft power into useful hydraulic work. Running far left of BEP (throttled discharge) recirculates liquid inside the casing, heats it, and loads the bearings radially. Running far right starves the suction and invites cavitation. A good selection keeps continuous duty within roughly 70–110% of BEP flow.
The other lines on the curve
The power curve shows the motor load across the range — check that the motor is not overloaded at the far right of the curve if your system could ever run there. The efficiency curves (the arcs) show the efficiency islands around BEP. The NPSH-required curve, rising steeply at high flows, tells you the minimum suction pressure the pump needs; your installation must provide more, with margin.
A worked example
You need 20 m³/hr of water-like liquid against a calculated system head of 28 m. On our PP/PVDF magnetic drive curve, 20 m³/hr at 28 m sits inside the efficient band of the mid-size impeller — a clean selection. Had the required head been 40 m, the same casing would sit at the far left of its curve; we would move you to the process pump range instead of letting you run a pump throttled to death.
The practical takeaway
Send us three numbers — flow, total head, and liquid — and we return a selection with the duty point plotted on the test curve. Ten minutes of curve reading at the enquiry stage prevents years of seal failures, vibration and energy waste on the shop floor.
Have a duty point to discuss?
Send it over — an applications engineer responds within 24 working hours.