BIZOMAT MAKEOS · Pneumatics
Pneumatic Cylinder Air Demand
What reference-volume air demand does this cylinder cycle create?
Estimate ideal reference-volume consumption for a double-acting cylinder using absolute pressure and temperature.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Bore diameter | mm | Cylinder datasheet. |
| Rod diameter | mm | Rod diameter; single rod cylinder. |
| Stroke | mm | Travel per extension or retraction. |
| Supply gauge pressure | bar gauge | Working pressure at the cylinder. |
| Local ambient pressure | bar absolute | Local atmospheric pressure used to convert gauge to absolute. |
| Reference pressure | bar absolute | Pressure at which the reported litres are expressed. |
| Cylinder air temperature | °C | Average absolute-gas calculation temperature during filling. |
| Reference temperature | °C | Temperature at which the reported litres are expressed. |
| Complete cycles per minute | cycles/min | One extension plus one retraction is one complete cycle. |
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 diameter
- What it is
- The inside diameter of the cylinder barrel, which equals the piston diameter, from the cylinder datasheet.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.001 mm to 1000000 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 demand rises with roughly the square of bore.
- Get it right
- Use the nominal bore size, not the outside dimension of the cylinder profile.
What this means: Rod diameter
- What it is
- The diameter of the single piston rod, which takes up space in the rod-side chamber during retraction.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 1000000 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 reduces the retraction volume and so the air demand.
- Get it right
- It must be smaller than the bore; enter 0 if the cylinder has no rod-side reduction.
What this means: Stroke
- What it is
- The distance the piston travels in one extension or one retraction.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.001 mm to 1000000 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 demand is directly proportional to stroke.
- Get it right
- Use the stroke actually used in operation, not just the catalogue maximum.
What this means: Supply gauge pressure
- What it is
- The working supply pressure at the cylinder, read as gauge pressure (above local atmosphere).
- Units and format
- Enter a number in bar gauge: bar gauge. The form accepts 0 bar gauge to 100 bar gauge. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 bar gauge as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Air demand rises in proportion to absolute pressure (gauge plus ambient).
- Get it right
- Gauge pressure is what a normal gauge shows; the tool adds ambient pressure to make it absolute.
What this means: Local ambient pressure
- What it is
- The local atmospheric pressure, as an absolute pressure, used to convert the gauge supply pressure to absolute.
- Units and format
- Enter a number in bar absolute: bar absolute. The form accepts 0.001 bar absolute to 5 bar absolute. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 bar absolute as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- It adds to the gauge pressure, so a higher value raises demand slightly.
- Get it right
- It falls with altitude; use a local barometric value if you need precision.
What this means: Reference pressure
- What it is
- The absolute pressure at which you want the air volumes reported, for example the reference used by your compressor supplier.
- Units and format
- Enter a number in bar absolute: bar absolute. The form accepts 0.001 bar absolute to 5 bar absolute. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 bar absolute as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Reported litres are inversely proportional to the reference pressure.
- Get it right
- Match the reference condition used on the compressor or flow meter data you compare with.
What this means: Cylinder air temperature
- What it is
- The average temperature of the air in the cylinder while it fills, used for the gas-law conversion.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -273.14 °C to 1000 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Warmer cylinder air reduces the reported reference volume slightly.
- Get it right
- Enter °C; the tool converts to absolute temperature by adding 273.15.
What this means: Reference temperature
- What it is
- The temperature at which you want the air volumes reported, matching your compressor or flow data reference.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -273.14 °C to 1000 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Reported litres rise in proportion to absolute reference temperature.
- Get it right
- Use the same reference temperature as the supplier data you compare with.
What this means: Complete cycles per minute
- What it is
- How many complete cycles the cylinder makes each minute, counting one extension plus one retraction as one cycle.
- Units and format
- Enter a number in cycles/min: cycles/min. The form accepts 0 cycles/min to 10000 cycles/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 cycles/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Air demand per minute is directly proportional to cycles per minute.
- Get it right
- Do not count each stroke as a cycle; one out-and-back movement is one cycle.
Method and formulas
- Swept volume per full cycle (L) = [π × bore² / 4 + π × (bore² − rod²) / 4] × stroke / 10⁶.
- Absolute working pressure = gauge pressure + local ambient pressure.
- Reference litres/cycle = swept litres × (working absolute pressure / reference pressure) × ((reference °C + 273.15) / (cylinder °C + 273.15)).
- Multiply by complete cycles/min for reference L/min. At 50/20 mm, 100 mm stroke, 6 bar gauge plus 1 bar ambient and equal temperatures, the example uses 2.528982 reference L/cycle.
Limitations
- Ideal gas and swept chamber volumes only; tubing, dead volumes, leaks and valve losses are excluded.
- This is mean demand, not peak valve flow or compressor selection. Reference conditions must match when comparing air ratings.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- compressed air
- air consumption
- cylinder demand
Who it is for
- Automation engineers
- Maintenance teams
What you get
- Swept volume / complete cycle
- Working absolute pressure
- Reference volume / cycle
- Mean reference air demand
- Reference conditions
Interpreting the result
- Add measured leakage and auxiliary volumes, then check peak flow and pressure drop.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed CD pp. 3027–3036, 3421–3422. Topic reference; no source tables or recommended settings are reproduced.
- NASA Glenn: Equation of State (ideal-gas relationship) — https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/equation-of-state/
- Festo: Air consumption of cylinders — https://www.festo.com/ca/en/s/air-consumption
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
Pneumatics by the Numbers
What it covers: Size a pneumatic cylinder, time and cushion its stroke, choose valves and a safe fail state, count air and leak costs, supply clean air and commission and maintain the system.
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.