|Formation of cavitation|
Cavitation is very destructive and may wear out the trim and body parts of the valve in short time. Using hard internal materials provide a little improvement, but the harder materials also cost more and their use must be justified.
How can you minimize cavitation in control valves? You can change the process conditions and reduce operating temperatures. This may lower the vapor pressure enough to stop cavitation. Reducing the differential pressure across the valve can relieve or lower cavitation. Locating a control valve in the lowest elevation of the piping system and keeping the control valve as close as possible to the pump are also recommended practices.
Here is an excellent and thorough technical paper on cavitation in control valves courtesy of Samson Controls.