Pressure dips to its lowest point just past the restriction, at the vena contracta. If that dips below the liquid's vapor pressure, bubbles form, then implode as pressure recovers downstream, hammering trim and body walls with micro-jets that leave rough, cinder-like pits. It sounds like gravel in the line. Fixes include staged anti-cavitation trims, low-recovery valve styles and splitting the pressure drop across two valves.
Hear that gravel noise on the boiler feed recirc valve? That's cavitation, and the plug will look like a sponge.
Cavitation damage looks like rough, cinder-like pitting; flashing damage looks smooth and polished. Reading the trim tells you which one you have.
Also heard as
- cavitating
Do not mix it up with
- Flashing: In cavitation the bubbles collapse because pressure recovers; in flashing pressure stays below vapor pressure and the vapor carries on downstream.
Related terms
Flashing
Liquid partly turning to vapor through a valve because downstream pressure stays below its vapor pressure.
Cage
A slotted or drilled sleeve around a control valve plug that guides it and shapes how flow changes with travel.
Trim
The replaceable internal parts of a valve that touch the process fluid, such as seat, disc or plug, stem and cage.
Cv
Flow coefficient: US gallons per minute of 60 degree F water a valve passes with a 1 psi pressure drop.