Pneumatic Valve Sizing Calculator

Calculate required valve Cv/Kv flow coefficient for pneumatic systems with sub-critical and critical (choked) flow analysis.

Inputs

Required flow (SCFM)

Inlet pressure (PSIG)

Outlet pressure (PSIG)

Air temperature (°F)

Gas specific gravity

Sizing safety factor

Tab to move between fields

Results

Selected valve Cv

0.1

Calculated Cv (exact)0.02

Cv with safety factor0.03

Required Kv (metric)0.02

Selected valve max flow (SCFM)85.7

Flow regime (1=subsonic, 2=choked)1

Equivalent orifice (in)0.08

Suggested port size (NPT in)0.13

Kv With Safety0.03

How to Use This Calculator

Enter Required flow (SCFM), Inlet pressure (PSIG), and Outlet pressure (PSIG).
Set Air temperature (°F), Gas specific gravity, and Sizing safety factor.
Review the Selected valve Cv result.
Use Calculated Cv (exact) and Cv with safety factor to inform your decision.

What each input means

Required flow (SCFM): Standard cubic feet per minute of air required.
Inlet pressure (PSIG): Gauge pressure at the valve inlet.
Outlet pressure (PSIG): Gauge pressure at the valve outlet.
Air temperature (°F): Air temperature at the valve.
Gas specific gravity: Specific gravity relative to air (air = 1.0, nitrogen = 0.97).
Sizing safety factor: Extra Cv capacity for margin (25% typical).

What each result means

Selected valve Cv: Next standard Cv size that meets requirements with safety factor.
Calculated Cv (exact): Minimum Cv from flow conditions (before safety factor).
Cv with safety factor: Required Cv including sizing safety margin.
Required Kv (metric): Flow coefficient in metric units (Kv = Cv × 0.865).
Selected valve max flow (SCFM): Maximum SCFM capacity of the selected valve.
Flow regime (1=subsonic, 2=choked): 1 = sub-critical (normal), 2 = critical/choked flow.
Equivalent orifice (in): Equivalent sharp-edge orifice diameter for the selected Cv.
Suggested port size (NPT in): Recommended NPT port size for the selected Cv.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Required flow (SCFM) = 20, Inlet pressure (PSIG) = 90, Outlet pressure (PSIG) = 75, Air temperature (°F) = 70 = 6 input(s) provided
Calculate Selected valve Cv
Selected valve Cv
0.1 = 0.1
Calculate Calculated Cv
Calculated Cv
0.023 = 0.023
Calculate Cv with safety factor
Cv with safety factor = cvRequired * safetyFactor
0.029 = 0.029

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