Pneumatics
Pneumatic Air Consumption Calculator
Estimate average free-air demand for one or more identical pneumatic cylinders. Enter bore, rod, stroke, gauge pressure and complete cycles per minute to see chamber volumes, per-cycle consumption and total flow at the stated reference pressure.
Your estimate
- Total free-air consumption
- 50.013 L/min
- Total free-air flow in m³/min
- 0.05 m³/min
- Total free-air flow in CFM
- 1.766 ft³/min
- Free air per complete cycle / cylinder
- 5.001 L
- Extension swept volume / cylinder
- 0.393 L
- Retraction swept volume / cylinder
- 0.33 L
- Free air per extension / cylinder
- 2.718 L
- Free air per retraction / cylinder
- 2.283 L
- Absolute operating pressure
- 7.013 bar(a)
Free-air estimates use 1.01325 bar absolute reference pressure, equal temperatures and ideal-gas behavior. Single-acting means air-powered extension and unpowered return. Dead volume, tubing, valves, leakage and pressure drops are excluded. These are average demands, not certified compressor or valve sizing.
Total free-air consumption: 50.013 L/min. Total free-air flow in m³/min: 0.05 m³/min. Total free-air flow in CFM: 1.766 ft³/min. Free air per complete cycle / cylinder: 5.001 L. Extension swept volume / cylinder: 0.393 L. Retraction swept volume / cylinder: 0.33 L. Free air per extension / cylinder: 2.718 L. Free air per retraction / cylinder: 2.283 L. Absolute operating pressure: 7.013 bar(a)
Cylinder volume and free-air conversion
Extension swept volume Vext = πD²L/4. Retraction swept volume Vret = π(D² − d²)L/4. With dimensions in millimetres, divide cubic millimetres by 1000000 for litres. Extension and retraction are calculated separately for double-acting cylinders.
At equal temperature, the ideal-gas free-air equivalent is Vfree = Vswept × Pabsolute / Preference. This model uses Preference = 1.01325 bar absolute and Pabsolute = gauge pressure + 1.01325 bar, assuming the same atmospheric pressure at the cylinder and reference conditions.
One stroke versus one complete cycle
A double-acting cycle has one air-powered extension and one air-powered retraction. Consumption per cycle is (Vext + Vret) × pressure ratio. The rod occupies volume, so the stroke quantities are usually unequal.
Single-acting mode assumes air-powered extension and an unpowered, usually spring-driven, return. Only extension air is counted. Reverse-acting or other arrangements need a different model.
Pressure, cycle rate and cylinder count
Free-air demand scales with absolute pressure ratio, not gauge pressure alone. Increasing gauge pressure from 3 to 6 bar does not exactly double the ratio, because atmospheric pressure is added first. Check force requirements before selecting pressure.
Total L/min = free-air litres per cycle per cylinder × cycles per minute × cylinder count. Each cylinder runs at the entered rate; a blank count means one. Zero cycles produces zero minute consumption while the per-cycle quantity remains visible.
Interpreting L/min, m³/min and CFM
Swept volumes are geometric chamber volumes. Free-air stroke, cycle and flow results instead describe equivalent air at 1.01325 bar absolute and equal temperature. Keep these quantities separate.
Divide L/min by 1000 for m³/min or by 28.316846592 for cubic feet per minute. CFM here uses that same reference; it is not a claim of standardized SCFM or normal litres under a particular temperature standard.
Compressor sizing considerations
This is average cylinder demand, not compressor selection. Valves and tubing must also support peak flow during motion. Simultaneous actuators can create peaks much larger than the average; receivers and the network influence pressure stability.
Real systems use extra air through leakage, pilots, tubing and dead volumes. Pressure losses, temperature and system efficiency affect operation. Compare demand with compressor delivered capacity at the relevant pressure and reference conditions, using a justified margin.
Model boundaries
Assumptions include ideal gas, equal temperatures, full strokes, identical cylinders and a conventional single rod. Filling clearance volume and idle leaks are excluded. Zero gauge pressure returns a geometric atmospheric-volume equivalent but does not imply force to move the cylinder.
Use the related Cylinder Force Calculator to examine pressure and effective area. Neither result certifies the design or replaces manufacturer guidance.
Examples
Double-acting cylinder
- Input
- 50 mm bore, 20 mm rod, 200 mm stroke, 6 bar gauge, 10 complete cycles/min, 1 cylinder
- Result
- Extension swept volume 0.392699 L; retraction 0.329867 L; free air 5.001271 L/cycle and 50.013 L/min.
Single-acting extension
- Input
- Same dimensions and pressure, 10 cycles/min, air-powered extension with spring return
- Result
- Free air 2.718082 L/cycle; 27.181 L/min. No powered return volume is counted.
Four identical cylinders
- Input
- Double-acting example, 4 cylinders, each at 10 cycles/min
- Result
- 200.051 L/min total; 0.200051 m³/min; 7.065 CFM at the stated reference.
Frequently asked questions
Why add atmospheric pressure?
Gas volume ratios require absolute pressure. At 6 bar gauge, the model uses 7.01325 bar absolute divided by a 1.01325 bar reference.
Is a cycle one stroke?
No. A complete cycle is extension plus return. Double-acting mode includes air for both directions; single-acting mode counts powered extension only.
Are L/min results compressed chamber volume?
No. Flow results are free-air equivalents at the stated reference pressure and equal temperature. Swept volumes are shown separately.
Does rod diameter affect consumption?
Yes, for the powered return of a double-acting cylinder. A larger rod reduces annular return volume but leaves extension volume unchanged.
Does this include leaks and tubing?
No. Add justified allowances for valves, dead space, leakage and actual installation conditions.
Can this select a compressor directly?
No. Consider delivered capacity, reference conditions, other users, duty cycle, simultaneous demand, pressure losses and reserve margin.
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