Cavitation occurs when the pump discharge is extremely high. It normally occurs in a pump
that is running at less than 10% of its best efficiency point. The high discharge pressure
causes the majority of the fluid to circulate inside the pump instead of being allowed to
flow out the discharge. As the liquid flows around the impeller it must pass through the
small clearance between the impeller and the pump cutwater at extremely high velocity.
This velocity causes a vacuum to develop at the cutwater similar to what occurs in a
venturi and turns the liquid into a vapor. A pump that has been operating under these
conditions shows premature wear of the impeller vane tips and the pump cutwater. In
addition due to the high pressure condition premature failure of the pump mechanical seal
and bearings can be expected and under extreme conditions will break the impeller shaft.