Cavitation

The  formation, growth and collapse of vapour filled cavities or bubbles in a flowing liquid due to local fall in fluid pressure is called cavitation. The cavitation in a hydraulic machine affects in the following ways:

a) It causes noise and vibration of various parts.
b) It makes surface rough.
c) It reduces the discharge of a turbine.
d) It causes sudden drop in power output and efficiency.

The cavitation in reaction turbines can be avoided to a great extent by usins the following methods:

a) By installing the turbine below the tail race level.
b) By using stainless steel runner of the turbine.
c) By providing highly polished blades to the runner.
d) By running the turbine runner to the designed speed.