Answer / rajesh.

When a fluid passes a valve the fluid velocity increases. If the speed through the valve is high enough, the pressure in the liquid may drop to a level where the fluid may start bubble or flash. The pressure recovers sufficiently and the bubbles collapse upon themselves.
This situation is extremely destructive and may wear out the trim and body parts of the valve in short time which called Cavitation.
With an increasing fluid temperature the possibility for cavitation increases.

Cavitation can be avoided by using more than one control valve or more convenient - a multistage control valve.

I have a problem with a valve (air to close). When it is fully closed and try to open 1% it doesn't responce till 3% open suddenly more than 3% then back to 3%. I tried to tune positioner then removed it, the problem still exist. Any idea

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