Control Valve · Glossary

What is Flow Coefficient (Cv)?

Symbol: CvUS gpm at 1 psiControl Valve

Flow coefficient Cv is the flow of water in US gallons per minute through a valve with a pressure drop of 1 psi.

Flow Coefficient (Cv) Explained

Cv states the capacity of a valve at a given opening. Sizing calculates the Cv needed for the process, then a valve is chosen whose rated Cv covers it at a sensible opening.

IEC 60534-2-1 gives the full sizing equations with correction factors for piping, viscosity, choked flow and gas expansion.

Flow Coefficient (Cv) Formula

Cv = Q × √(SG ÷ ΔP) and Cv = 1.156 × Kv

Q	liquid flow (US gpm)
SG	specific gravity
ΔP	pressure drop (psi)
Kv	metric flow factor

Example: 200 gpm of water at 25 psi drop: Cv = 200 × √(1 ÷ 25) = 40.

Calculators for Flow Coefficient (Cv)

CalculatorCv Calculator for LiquidsFree online calculator with formula and worked example.CalculatorGas Valve Sizing CalculatorFree online calculator with formula and worked example.CalculatorCv Series and Parallel 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.Free downloadControl Valve Cheat SheetFree printable PDF cheat sheet.

Frequently Asked Questions

What is Flow Coefficient (Cv)?

Flow coefficient Cv is the flow of water in US gallons per minute through a valve with a pressure drop of 1 psi.

Why is Cv not a fixed number for a valve?

It changes with opening; data sheets give Cv at each travel, and the rated Cv at full open.

Can I add Cv of two valves?

In parallel, yes. In series, combine as 1/Cv² = 1/Cv₁² + 1/Cv₂².

Learn more on the blog

Control valve flow coefficient (Cv and Kv)

A practical guide on instrumentationblog.in with more detail on flow coefficient (Cv) and how it is applied on real plants.

Read Full Article

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