Calculate the Net Positive Suction Head available (NPSHa) and check it against the pump’s required NPSH. Pick a positive-displacement pump — triple-screw, gear, lobe, liquid-ring or AODD — and its required NPSH (NPIPr) auto-fills; enter the suction pressure, vapour pressure, static head and friction loss to get NPSHa, the margin and a pass/fail verdict, with a reference table of best-efficiency flow and materials for every pump.
Cavitation occurs when the local pressure at the pump inlet falls to the liquid’s vapour pressure, flashing vapour bubbles that collapse violently and erode the pump. To avoid it, the Net Positive Suction Head available (NPSHa) at the inlet must comfortably exceed the NPSH required (NPSHr) by the pump — for positive-displacement pumps this required value is the Net Positive Inlet Pressure required (NPIPr).
Values are computed from first-principles hydraulics and published pump data. Confirm the pump’s NPSHr at the actual duty point and speed with the manufacturer’s curve before finalising the installation.
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