Pneumatic Valve Cv Calculator
SI
Imp
Imperial
Inputs
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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.
Results
Default result
Edit inputs
Required valve Cv
1.11
Pass
Subcritical shortcut range.
Also computed
Downstream / upstream pressure
(P₂/P₁)
0.903
Pressure drop
(ΔP)
0.7
bar
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.
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