How it works
- what a pump gives you — A centrifugal pump has no fixed output. It has a curve — head falling as flow rises. Ask it for more flow and it gives you less head, whether you wanted that or not.
- the system curve — The pipework answers with its own curve: a fixed static head you must lift against, plus friction that grows with the square of flow. Static lift is there at zero flow; friction is nothing at zero flow and dominates at the top end.
- the duty point — The pump runs where the two curves cross, and nowhere else. You do not choose the flow — you choose the two curves, and the intersection chooses the flow. Close a valve and you steepen the system curve, walking the duty point up and to the left.
- NPSH and cavitation — The suction side is where pumps are actually killed. If absolute head at the impeller eye falls to the vapour pressure, water flashes to steam, the bubbles collapse on the vane, and the impeller erodes. Keep NPSH available above NPSH required with a metre in hand — and remember hot water leaves you far less room.
- what governs it — Head sets the duty point, efficiency sets the power bill, and NPSH decides whether the pump survives. Push the temperature up or the suction level down and watch the margin close: that is the number that strands installations, not the head.
Design parameters
The panel opposite runs the same correlations as the P-200 design sheet, so the animation and the calculator cannot disagree. Drag any of them and the picture responds.
- Design flow — m³/h
- Static head — m
- Friction at design flow — m
- Pump efficiency — %
- Suction lift (−) / head (+) — m
- Water temperature — °C
Open the full P-200 design sheet for the governing equations, the accepted design envelopes and the worked calculation.