What is meant by cavitations in control valve?

When a liquid enters a valve and the static pressure at the vena contractadrops to less than the fluid vapor pressure and the recovering to above fluid vapourpressure, this pressure recovery causes an implosion or collapse of the vapourbubbles formed at the vena contracta. This condition is called cavitation.

Formation of bubbles & colapsing of bubbles due to loss of NPSH( Net Posative Suctio Head) inside the pump/valves produces resonance/ enormous stress, if it continue for alonger time it may rapture the valves or pump is known as cavitation.

the internal part wear out of bubbles and force of water gradually !!!