Pneumatic Valve Cv Calculator

Inputs

Required air flow (Q)

Free-air flow through the valve.

Nl/min

Upstream pressure (P₁)

Gauge pressure before the valve.

bar

Downstream pressure (P₂)

Gauge pressure after the valve.

bar

Gas temperature (T)

Gas temperature used in the shortcut equation.

°C

Gas specific gravity (SG)

Specific gravity relative to air. Use 1.0 for air.

Default result

Required valve Cv

1.11

Pass

Subcritical shortcut range.

Also computed

Downstream / upstream pressure(P₂/P₁)0.903

Pressure drop(ΔP)0.7bar

Method notes 2 notes

This is a screening estimate for dry air using the common subcritical Cv shortcut. For final valve selection use the valve maker flow curves or ISO 6358/ISA sizing data.
When downstream/upstream absolute pressure ratio drops below about 0.53, air flow is choked; increasing pressure drop will not raise flow the same way.