# Pneumatic Valve Sizing

• All stated pneumatic formulas assume 68 degrees F at sea level
• All strokes and diameters are in inches
• All times are in seconds
• All pressures are PSI

### Valve Sizing for Cylinder Actuation

SCFM = 0.0273 x Cylinder Diameter x Cylinder Diameter x Cylinder Stroke / Stroke Time x ((Pressure-Pressure Drop)+14.7) / 14.7
Cv Required = 1.024 x SCFM / (Square Root of (Pressure Drop x (Pressure-Pressure Drop+14.7)))
Pressure 2 (PSIG) = Pressure-Pressure Drop

### Air Flow Q (in SCFM) if Cv is Known

Valve Cv x (Square Root of (Pressure Drop x ((PSIG - Pressure Drop) + 14.7))) / 1.024

### Cv if Air Flow Q (in SCFM) is Known

1.024 x Air Flow / (Square Root of (Pressure Drop x ((PSIG-Pressure Drop) + 14.7)))

### Air Flow Q (in SCFM) to Atmosphere

SCFM to Atmosphere = Valve Cv x (Square Root of (((Primary Pressure x 0.46) + 14.7) x (Primary Pressure x 0.54))) / 1.024
Pressure Drop Max (PSIG) = Primary Pressure x 0.54

### Flow Coefficient for Smooth Wall Tubing

Cv of Tubing =(42.3 x Tube I.D. x Tube I.D. x 0.7854 x (Square Root (Tube I.D. / 0.02 x Length of Tube x 12)
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