Cavitation in end-suction pumps: cause, symptoms and cure

Cavitation happens when the pressure at the impeller eye falls below the vapour pressure of the liquid. The bubbles that form collapse a fraction of a second later, and the resulting micro-jets erode the impeller surface until it looks like it has been shot-blasted.

The symptoms are usually noticed before the damage: a rattling or gravel-like noise from the casing, a flow rate that wanders, vibration that appears only at certain duties, and a discharge pressure that never quite reaches the curve. If the impeller is inspected and the damage is concentrated on the suction side of the vanes, cavitation is the first suspect.

The cure is almost always on the suction side of the installation rather than in the pump. Check the net positive suction head available against the figure in the datasheet, look for a strainer that has been allowed to block, a suction line one size too small, an elbow fitted directly onto the inlet, or a liquid hotter than the original design case.

Where the installation cannot be changed, a low-NPSH impeller or a slower-running pump will often recover the duty. Both are worth costing against the price of repeated impeller replacement.

Send us the duty point, the fluid temperature and a photograph of the damaged impeller and we can normally confirm the cause and quote the right fix from the existing range.