Cavitation happens when pressure at the pump inlet drops below the vapour pressure of the liquid. Vapour bubbles form, travel into the higher-pressure part of the impeller, and collapse violently. Each collapse removes a tiny amount of metal.
How to recognise it
A distinctive rattling sound, often described as pumping gravel. Alongside it: vibration, fluctuating flow and pressure, and falling performance. Left running, it pits the impeller, damages seals and bearings, and eventually destroys the pump.
The root cause
Available NPSH is lower than the NPSH the pump requires. In practice that usually means the suction line is too long, too narrow, partially blocked, or the pump sits too high above the water source. Hot liquids make it worse, because vapour pressure rises with temperature.
Prevention
Keep the suction line short, straight and generously sized. Fit a strainer and keep it clean. Reduce the static lift where possible. And at selection stage, confirm available NPSH exceeds the pump requirement with a margin — not just barely.
