Cavitation

• Cavitation: Cavitation is defined as the phenomenon of formation of vapor bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure and the sudden collapsing of these vapor bubbles in a region of high pressure. When the vapor bubbles collapse, a very high pressure is created. The metallic surface, above which the liquid is flowing, is subjected to these high pressures, which cause pitting action on the surface. Thus cavities are formed on the metallic surface and also considerable noise and vibrations are produced.

Precaution against cavitation: the following precautions should be taken against cavitation:
i) The pressure of the flowing liquid in any part of the hydraulic system should not be allowed to fall below its vapor pressure. If the flowing liquid is water, then the absolute pressure head should not be below 2.5m of water.
ii) The special materials or coatings such as aluminium-bronze and ss, which are cavitation resistant materials, should be used.
Effects of cavitation: the following effects of cavitations:
i) The metallic surfaces are damaged and cavities are formed on the surfaces.
ii) Due to sudden collapse of vapor bubble, considerable noise and vibrations are produced.
iii) The efficiency of a turbine decreases due to cavitation. The work done by water or output horse power becomes less and thus efficiency decreases.