BIZOMAT MAKEOS · Pneumatics
Pneumatic Cylinder Sizing, Air Use and Running Cost
What bore does this air cylinder need, how much air does it use, and what does that air cost?
Sizing of a double-acting pneumatic cylinder: minimum bore for the load at a recommended load ratio, the next standard bore, extend and retract forces, free air per cycle and average consumption (as the cylinder air consumption tool), peak flow while extending at speed, kinetic energy against the cushion capacity, and the yearly energy cost of the air.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Load force | N | Force the cylinder must produce while moving. |
| Maximum load ratio | % | Largest share of theoretical force to use (about 50–70% for dynamic loads). |
| Supply pressure | bar g | Supply pressure at the cylinder. |
| Rod diameter | mm | Rod diameter of the chosen cylinder. |
| Stroke | mm | Stroke length. |
| Cycles per minute | Full cycles (extend and retract) per minute. | |
| Extend speed | m/s | Piston speed while extending. |
| Moving mass | kg | Mass moved by the piston. |
| Cushion energy capacity | J | Energy the end cushion can absorb (from the cylinder maker). |
| Compressor specific power | kW per m³/min | Compressor power per unit of free air delivered. |
| Running hours per year | h | Hours per year the machine cycles. |
| Electricity price | $/kWh | Cost of electricity. |
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: Load force
- What it is
- Force the cylinder must deliver while moving the load on the extend stroke: the load itself, friction and any process force.
- Units and format
- Enter a number in N: newtons. The form accepts 0.000001 N to 1000000 N. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 600 N as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The minimum bore rises with the square root of force.
What this means: Maximum load ratio
- What it is
- Largest share of the cylinder’s theoretical force you will use, leaving the rest for seal friction, acceleration and pressure drop.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 10% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 70% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A lower ratio needs a larger bore.
- Get it right
- Type the percentage; a lower load ratio gives a larger bore and steadier motion.
What this means: Supply pressure
- What it is
- Air pressure available at the cylinder port while it moves, as gauge pressure above atmosphere.
- Units and format
- Enter a number in bar g: bar g. The form accepts 0.000001 bar g to 16 bar g. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 bar g as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Higher pressure lowers the minimum bore.
- Get it right
- Gauge pressure, as read on a regulator gauge; the tool adds atmospheric pressure itself for air use. Use the pressure after valve and tubing losses.
What this means: Rod diameter
- What it is
- Diameter of the piston rod of the cylinder you plan to use, from the maker’s catalogue. It reduces the retract force and the air used on the return stroke.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 200 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.
- Get it right
- It must be smaller than the standard bore the tool picks.
What this means: Stroke
- What it is
- Distance the piston travels from fully retracted to fully extended.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 5000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 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 per cycle rises in proportion to stroke.
What this means: Cycles per minute
- What it is
- Number of complete extend-and-retract cycles the cylinder makes each minute while the machine runs.
- Units and format
- Enter a plain number with no unit. The form accepts 0.000001 to 1000. 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
- Average air use and yearly cost rise in proportion.
- Get it right
- One cycle is out and back; do not count each stroke separately.
What this means: Extend speed
- What it is
- Piston speed while extending. It sets the peak air flow and the kinetic energy to be absorbed at the end of the stroke.
- Units and format
- Enter a number in m/s: metres per second. The form accepts 0.000001 m/s to 5 m/s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.3 m/s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Kinetic energy at the end of stroke rises with the square of speed.
What this means: Moving mass
- What it is
- Mass that moves with the piston: the load, tooling, brackets and the piston and rod themselves.
- Units and format
- Enter a number in kg: kilograms. The form accepts 0 kg to 10000 kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Kinetic energy at the end of stroke is proportional to moving mass.
What this means: Cushion energy capacity
- What it is
- Energy the cylinder’s end-of-stroke cushion can absorb, from the cylinder maker’s catalogue for the bore and cushion type.
- Units and format
- Enter a number in J: joules. The form accepts 0 J to 10000 J. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.5 J as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- If the moving load has more energy than this, an external shock absorber or slower end speed is needed.
What this means: Compressor specific power
- What it is
- Electrical power the compressor draws for each cubic metre per minute of free air it delivers, from its data sheet or measured power and flow.
- Units and format
- Enter a number in kW per m³/min: kW per m³/min. The form accepts 0.000001 kW per m³/min to 20 kW per m³/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6.5 kW per m³/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Yearly air cost rises in direct proportion.
- Get it right
- Use free air delivered, not compressed volume; a measured figure for your system is better than a catalogue one.
What this means: Running hours per year
- What it is
- Hours per year the machine actually cycles this cylinder.
- Units and format
- Enter a number in h: hours. The form accepts 0.000001 h to 8760 h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4000 h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Yearly air cost rises in direct proportion.
- Get it right
- Count running hours, not the hours the plant is open; an idle cylinder uses no air.
What this means: Electricity price
- What it is
- What you pay for one kilowatt-hour of electricity, including network charges, from your power bill or contract.
- Units and format
- Enter a number in $/kWh: money per kilowatt-hour. The form accepts $0/kWh to $10/kWh. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with $0.25/kWh as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Yearly air cost rises in direct proportion.
Method and formulas
- Minimum bore = √[4F ÷ (π p × ratio)]; next ISO bore from 8 to 320 mm.
- Air per cycle, as free air = (2A − A_rod) × stroke × (p + 1.013) ÷ 1.013.
- Peak free-air flow while extending = A v (p + 1.013) ÷ 1.013.
- Kinetic energy = ½ m v² against the cushion capacity; air cost = consumption × specific power × hours × price.
- Example: 600 N at 6 bar needs a 50 mm bore using 25.006 L/min of free air.
Limitations
- Theoretical forces; seal friction and pressure drop in valves and tubing reduce them.
- Isothermal air use; real use is higher with long tubing to the valve.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose a cylinder bore for an automation task
- Estimate compressed-air demand for a new machine
- Show the energy cost of cylinder air
Who it is for
- Automation engineers
- Machine designers
- Maintenance engineers
What you get
- Minimum and standard bore with forces
- Air per cycle, average consumption and peak flow
- Cushioning check and air cost
Interpreting the result
- Oversized cylinders waste air every stroke; lower pressure on the return stroke saves more.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3421–3425, 3030–3037. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Free air, pressure and mass flow
In Compressed Air Plant by the Numbers
What it covers: Work out what a cubic metre of compressed air means, convert free air delivery to mass and actual volume, state pressure ratios in absolute terms and meet the CA-1 compressor room.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
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