Control Valve · Glossary

What is Cavitation?

vapour bubble collapseControl Valve

Cavitation is the formation and violent collapse of vapour bubbles when liquid pressure drops below vapour pressure in a valve and then recovers.

Cavitation Explained

At the vena contracta, liquid speeds up and pressure falls. If it falls below the vapour pressure, bubbles form; as pressure recovers downstream they collapse, causing noise, vibration and pitting of the trim and body.

It is reduced with low recovery valves, anti cavitation trims that drop pressure in stages, or by placing the valve where the pressure is higher.

Cavitation Formula

σ = (P₁ − P_v) ÷ (P₁ − P₂)

P₁, P₂	upstream and downstream absolute pressure
P_v	vapour pressure

Example: P₁ = 10 bar a, P₂ = 4 bar a, P_v = 0.03 bar a: σ ≈ 1.66. Compare with the maker limits for the valve.

Calculators for Cavitation

CalculatorCavitation Index CalculatorFree online calculator with formula and worked example.CalculatorCv Calculator for LiquidsFree online calculator with formula and worked example.

Free Downloads

Free downloadControl Valve Sizing Excel SheetFree download in Excel and PDF.Free downloadControl Valve Cheat SheetFree printable PDF cheat sheet.

Frequently Asked Questions

What is Cavitation?

Cavitation is the formation and violent collapse of vapour bubbles when liquid pressure drops below vapour pressure in a valve and then recovers.

What does cavitation sound like?

Like gravel flowing through the pipe.

Is cavitation the same as flashing?

No. In cavitation the bubbles collapse as pressure recovers; in flashing the outlet pressure stays below vapour pressure and the bubbles remain.

Learn more on the blog

Control valve passing causes

A practical guide on instrumentationblog.in with more detail on cavitation and how it is applied on real plants.

Read Full Article

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