NPSH and Cavitation: What Pump Users Should Check

Cavitation occurs when local liquid pressure falls below vapour pressure and vapour bubbles form and collapse inside the pump. Typical signs include crackling noise, vibration, unstable flow, reduced head and pitting on the impeller. NPSHa is determined by the installation. NPSHr is determined by the pump and operating point. Reliable operation requires NPSHa to exceed NPSHr with a suitable margin. To improve suction conditions, reduce suction-pipe losses, remove unnecessary fittings, increase pipe diameter, raise the liquid level, lower the liquid temperature where possible, avoid air pockets and keep strainers clean. Never treat noise alone as proof of cavitation. Confirm the operating point, pressure, temperature and system condition before changing equipment.