BIZOMAT MAKEOS · Pneumatics
Cylinder Air Consumption Check (Atmospheric Air per Cycle, Total Demand, Compressor Power)
How much compressed air do these cylinders use at their cycle rate, can my compressor supply it, and what shaft power does that take?
Air demand of double-acting pneumatic cylinders: the swept volume of the extend and return strokes with an allowance for dead volume and hoses, the atmospheric air per cycle at the working pressure, the total demand for the number of cylinders and their cycle rate plus a leakage allowance, and the theoretical and shaft power to compress it (as the compressor power tool), against the delivery of the compressor.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Bore | mm | Cylinder bore. |
| Rod diameter | mm | Rod diameter (the return stroke uses less air). |
| Stroke | mm | Cylinder stroke. |
| Cycles per minute (out and back) | Complete out-and-back cycles per minute of each cylinder. | |
| Number of cylinders | Number of identical cylinders. | |
| Working pressure (gauge) | bar | Working pressure. |
| Dead volume and hoses | % | Extra volume in ports, cushions and hoses as a share of the swept volume. |
| Leakage allowance | % | Allowance for leaks across the system. |
| Compressor | ||
| Compressor delivery (atmospheric air) | m³/min | Air the compressor delivers at this pressure, measured at atmospheric conditions. |
| Compression stages | stages | Number of compression stages. |
| Overall efficiency (adiabatic to shaft) | % | Overall compressor efficiency. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Bore
- What it is
- The inside diameter of each cylinder barrel. The full piston area fills on the extend stroke.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Air use grows roughly with the square of the bore.
- Get it right
- Use the nominal catalogue bore, not the barrel outside diameter.
What this means: Rod diameter
- What it is
- The diameter of the piston rod. The rod takes up space on the return side, so the return stroke uses less air.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger rod slightly reduces the air used on the return stroke.
- Get it right
- Take it from the catalogue for the chosen bore; it must be smaller than the bore.
What this means: Stroke
- What it is
- How far each piston travels in one direction. Every cycle fills the cylinder once each way over this length.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Air per cycle rises in direct proportion to the stroke.
- Get it right
- Use the travel the piston actually makes each stroke; for a cylinder that runs end to end this is its catalogue stroke.
What this means: Cycles per minute (out and back)
- What it is
- How many complete out-and-back cycles each cylinder makes per minute on average.
- Units and format
- Enter a plain number with no unit. The form accepts 0.000001 to 10000. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Total demand rises in direct proportion.
- Get it right
- Count a full cycle as out and back; one extend alone is half a cycle.
What this means: Number of cylinders
- What it is
- How many identical cylinders run at the same size, pressure and cycle rate.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 10000. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Total demand rises in direct proportion.
- Get it right
- Group different cylinders into separate runs of the tool and add the demands.
What this means: Working pressure (gauge)
- What it is
- The gauge pressure the cylinders are filled to on each stroke, set by the regulator feeding them.
- Units and format
- Enter a number in bar: bar (1 bar = 100 kPa). The form accepts 0.000001 bar to 50 bar. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 bar as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Higher pressure means more free air per cycle and more compressor power.
- Get it right
- Use gauge pressure; the tool adds atmospheric pressure itself to convert to free air.
What this means: Dead volume and hoses
- What it is
- Extra volume filled and exhausted each stroke beyond the swept volume: ports, cushions, fittings and the hose between valve and cylinder.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 200%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Long hoses between valve and cylinder add a lot; mount valves close to the cylinder to keep it small.
What this means: Leakage allowance
- What it is
- An allowance added to the total demand for air lost through leaks in fittings, hoses and valves across the system.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 200%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 15% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Total demand rises in direct proportion to one plus this allowance.
- Get it right
- Base it on a leak survey or the air drawn with all machines idle, rather than a guess.
Compressor
What this means: Compressor delivery (atmospheric air)
- What it is
- The free air delivery of the compressor: the volume of air it delivers per minute, measured at atmospheric conditions, at the working pressure.
- Units and format
- Enter a number in m³/min: cubic metres per minute. The form accepts 0.000001 m³/min to 100000 m³/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.5 m³/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the delivered (FAD) figure at your pressure from the compressor data sheet, not the swept or displacement volume.
What this means: Compression stages
- What it is
- The number of compression stages in the compressor, used in the ideal compression power formula.
- Units and format
- Enter a number in stages: stages. The form accepts 1 stages to 6 stages. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 stages as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from the compressor data sheet; it affects only the power estimate.
What this means: Overall efficiency (adiabatic to shaft)
- What it is
- The ratio of ideal adiabatic compression power to the shaft power the compressor actually draws.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 1% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 75% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A lower efficiency raises the shaft power estimate.
- Get it right
- Take it from the compressor data sheet or derive it from its rated shaft power and delivery.
Method and formulas
- Swept volume per cycle = (π D² ÷ 4 + π (D² − d²) ÷ 4) × stroke × (1 + dead volume).
- Atmospheric air = swept volume × (p + p_atm) ÷ p_atm; demand = free air × cycles × cylinders × (1 + leakage).
- Adiabatic and shaft power for the demand at the working pressure (as the compressor power tool).
- Example: 5.5014 L of atmospheric air per cycle; 253.06 L/min in total takes 1.4719 kW.
Limitations
- Cylinders filled to full pressure every stroke; pressure regulators on the return stroke save air.
- Average demand; short peaks need receiver volume.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a compressor before adding a machine
- Estimate the running cost of cylinders
- Compare bore sizes on air use
Who it is for
- Automation engineers
- Maintenance engineers
- Energy managers
What you get
- Atmospheric air per cycle
- Total demand
- Compressor capacity and power
Interpreting the result
- Air use grows with the square of the bore: one size down can save a third of the air.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3032–3041. Topic reference; no source tables or recommended settings are reproduced.
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