ABSTRACT
Cavitation is caused by local vaporization of the fluid, when the local static pressure of a liquid falls below the vapor pressure of the liquid. Small bubbles or cavities filled with vapor are formed, which suddenly collapse on moving forward with the flow into regions of high pressure. These bubbles collapse with tremendous force, giving rise to as high a pressure as 3500 atm. In a centrifugal pump, these low-pressure zones are generally at the impeller inlet, where the fluid is locally accelerated over the vane surfaces. In turbines, cavitation is most likely to occur at the downstream outlet end of a blade on the lowpressure leading face. When cavitation occurs, it causes the following undesirable effects:
1. Local pitting of the impeller and erosion of the metal surface. 2. Serious damage can occur from prolonged cavitation erosion. 3. Vibration of machine; noise is also generated in the form of sharp cracking sounds
when cavitation takes place. 4. A drop in efficiency due to vapor formation, which reduces the effective flow areas.
