Control Valve · Glossary

What is Liquid Pressure Recovery Factor?

Symbol: FLdimensionlessControl Valve

Liquid pressure recovery factor FL describes how much pressure a valve recovers after the vena contracta; a high FL means low recovery.

Liquid Pressure Recovery Factor Explained

Valves with a streamlined path, such as ball and butterfly valves, recover a lot of pressure (low FL) and so cavitate and choke at lower pressure drops. Globe valves recover less (high FL).

FL comes from valve tests and is given by the maker for each type and opening.

Liquid Pressure Recovery Factor Formula

F_L = √[(P₁ − P₂) ÷ (P₁ − P_vc)]

P_vc	pressure at the vena contracta
P₁, P₂	upstream and downstream pressure

Liquid Pressure Recovery Factor: Typical Values

Globe valve	about 0.85 to 0.9
Ball valve	about 0.55 to 0.6
Butterfly valve	about 0.55 to 0.7

Calculators for Liquid Pressure Recovery Factor

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 Cheat SheetFree printable PDF cheat sheet.

Frequently Asked Questions

What is Liquid Pressure Recovery Factor?

Liquid pressure recovery factor FL describes how much pressure a valve recovers after the vena contracta; a high FL means low recovery.

Why does a butterfly valve cavitate easily?

It recovers much of its pressure drop, so the vena contracta pressure is far below the outlet pressure.

Does FL change with opening?

Yes, usually it decreases as the valve opens.

Learn more on the blog

Control valve flow coefficient (Cv and Kv)

A practical guide on instrumentationblog.in with more detail on liquid pressure recovery factor and how it is applied on real plants.

Read Full Article

More Control Valve Terms

Valve termPiping Geometry FactorPiping geometry factor Fp corrects valve capacity for reducers and other fittings attached directly to…Valve termSeat Leakage ClassSeat leakage class is the maximum allowed flow through a closed valve, defined by ANSI/FCI 70-2 and IEC…Valve termFail Safe PositionFail safe position is the position a valve goes to on loss of air or signal: fail open, fail closed or…Valve termAir to OpenAir to open means air pressure on the actuator opens the valve and the spring closes it, so the valve…Valve termValve ActuatorA valve actuator is the device that produces the force or torque to move a valve, using air pressure,…Valve termSpring RangeSpring range is the air pressure range over which a spring diaphragm actuator moves through full stroke…

All control valve terms · Full glossary A to Z