Control Valve · Glossary

What is Choked Flow?

maximum flow through a valveControl Valve

Choked flow is the condition where flow through a valve stops increasing even though the downstream pressure is lowered further.

Choked Flow Explained

For liquids, choking happens when vapour forms at the vena contracta. For gases, it happens when the velocity at the vena contracta reaches sonic speed.

Sizing must use the choked pressure drop instead of the actual one, otherwise the valve is undersized.

Choked Flow Formula

ΔP_choked = F_L² × (P₁ − F_F P_v), F_F = 0.96 − 0.28 √(P_v ÷ P_c)

F_L	liquid pressure recovery factor
P_v, P_c	vapour and critical pressure
P₁	upstream absolute pressure

Example: Liquid sizing per IEC 60534-2-1. For gas, flow chokes when x ≥ F_γ x_T.

Calculators for Choked Flow

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

Free Downloads

Free downloadControl Valve Sizing Excel SheetFree download in Excel and PDF.Free downloadGas Control Valve Sizing Excel SheetFree download in Excel and PDF.

Frequently Asked Questions

What is Choked Flow?

Choked flow is the condition where flow through a valve stops increasing even though the downstream pressure is lowered further.

Does choked flow damage the valve?

Liquid choking means flashing or severe cavitation, which can. Gas choking itself is not damaging but causes noise.

Can I get more flow when choked?

Only by raising upstream pressure or using a larger valve.

Learn more on the blog

Control valve flow coefficient (Cv and Kv)

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

Read Full Article

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