A pump performance curve plots head (vertical axis) against flow (horizontal axis); where your required flow and head cross the curve is the duty point, and the pump should operate near its best efficiency there.
The two axes
The horizontal axis shows flow (Q), here in L/min and m³/h. The vertical axis shows total head (H) in metres. Each coloured line is one pump model. As flow increases, head falls — that falling line is the pump’s capability.
How to read it in four steps
- Find your flow on the bottom axis (convert units if needed).
- Go up until you meet the curve of the model you are considering.
- Read across to the head axis — that is the head the pump delivers at that flow.
- Compare with the head you need. If the curve is above your required head, the pump can do the job.
Worked example
Suppose a site needs 50 m³/h at 20 m head. Find 50 m³/h on the flow axis, go up to the curve and read across. If the curve shows 25 m of head at that flow, the pump can do the job with a healthy margin. If it shows only 15 m, the pump falls short and you need a larger model. (Illustrative numbers — always confirm against the manufacturer curve for the exact model.)
| Term | Meaning |
|---|---|
| Duty point | Flow and head required in your system |
| Shut-off head | Maximum head at zero flow |
| Maximum flow | Flow at the end of the curve (very low head) |
| Best efficiency point (BEP) | Flow where the pump is most efficient |
| System curve | Head the pipework needs at each flow |
Practical tips
- Operate between roughly 60 % and 120 % of the best-efficiency flow.
- Do not select a pump at the very end of the curve — it will be inefficient and wear faster.
- If your duty is between two models, choose the larger and throttle, or ask for a trimmed impeller.
- Check the speed — curves are specific to the rpm (here n=2860 r/min).
Browse our pump range or send us your duty for a recommendation.
Frequently asked questions
What is a pump performance curve?
A graph showing how much head a pump produces at different flow rates.
What is the duty point?
The point where the system curve meets the pump curve — the actual flow and head the pump will deliver in your installation.
What is shut-off head?
The maximum head a pump produces at zero flow.
Why should I leave a margin?
Wear, fouling and pipe changes shift the duty point. A 10–20 % margin protects performance.