Cavitation
Cavitation is the formation and subsequent collapse of vapour bubbles in a liquid when the local static pressure falls below the liquid's vapour pressure. In pumps it typically begins at the impeller inlet, where velocity is highest and pressure lowest; the bubbles are carried into higher-pressure regions and implode, producing shock waves and micro-jets that pit metal surfaces. Symptoms include a gravel-like noise, vibration, fluctuating discharge pressure, loss of head and flow, and eroded impeller vanes. The main causes are insufficient NPSH available, high liquid temperature, restricted or clogged suction lines, and operation far from the best efficiency point, including suction recirculation at low flow. Cavitation also occurs in control valves with high pressure drops. Preventive measures include raising suction pressure, reducing suction losses, lowering liquid temperature, using anti-cavitation valve trims and selecting cavitation-resistant materials.
Examples
- Pitting damage on a centrifugal pump impeller inlet
- Noise and vibration in a pump with a clogged suction strainer
- Anti-cavitation trim in a high-pressure-drop control valve