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Pneumatic cylinder air consumption and force

Enter bore, rod, stroke, pressure and cycle rate to see how much free air the cylinder uses, the peak flow, how much force it delivers and which standard bore carries the load. For several machines, paste the list from Excel.

Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.

Pre-sizing
Cylinder
Pressure and load
Dead volume and tubing (optional)

Enter zero for tube and dead volume to calculate from stroke only. Extend time gives the peak flow that sizes the valve and filter-regulator.

Several cylinders? Paste the list from Excel

One row per cylinder: name; bore; rod; stroke (mm or in, following the page units); cycles per minute; quantity; acting (2 = double, 1 = single). Pressure, tubing and dead volume above apply to all.

See what was read
—Free air consumption
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Consumption versus working pressure

Average free-air consumption of the set at the cycle rate entered. Each psi less saves air in proportion to absolute pressure.

Tap the chart to see the values.

Available force by standard bore

Extend force at the efficiency entered and working pressure, for ISO 6432 and ISO 15552 bores. The line is the load divided by the maximum ratio.

Tap the chart to see the values.

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Method, assumptions and references

Equations used

Areas: A = π D² ÷ 4; annulus An = A − π d² ÷ 4; compression ratio r = (p + p_atm) ÷ p_atm
Free air per cycle = r × [A·s·(1 + vm) + V_tube] + r × [An·s·(1 + vm) + V_tube] (second term for double acting only)
Average flow = air per cycle × cycles per minute × quantity; peak = r × [A·s·(1 + vm) + V_tube] ÷ extend time
Force: F_theoretical = p·A; F_available = p·A·η − F_spring; retract = p·An·η (double) or F_spring (single); D_min = √(4 (F + F_spring) ÷ (π p · ratio))

Assumptions and limits

  • Chamber filled to working pressure on every stroke and exhausted to atmosphere; free air referred to 14.7 psia and ambient temperature (FAD).
  • For single acting, spring force is taken at end of stroke (worst case) and only the cap-end chamber uses air.
  • An 80% to 90% efficiency covers seal friction; the maximum load ratio keeps force in reserve to accelerate the mass. Long rods in compression need a buckling check.
  • Standard rods: the most common ones in the ISO 15552 and ISO 6432 series; check the maker’s catalog.

Standards and technical documents

  • ISO 15552: Pneumatic fluid power — Cylinders with detachable mountings, 1 000 kPa (10 bar) series, bores from 32 mm to 320 mm
  • ISO 6432: Pneumatic fluid power — Single rod cylinders, 1 000 kPa (10 bar) series, bores from 8 mm to 25 mm
  • ISO 4414: Pneumatic fluid power — General rules and safety requirements for systems and their components
  • ISO 6358: Pneumatic fluid power — Determination of flow-rate characteristics of components
  • Festo Didactic: Pneumatics, basic level
  • Atlas Copco: Compressed Air Manual, 8th ed.

U.S. regulations

  • OSHA 29 CFR 1910.147: control of hazardous energy (lockout/tagout), including pneumatic energy
  • OSHA 29 CFR 1910.212: general requirements for machine guarding
  • ANSI B11.0: safety of machinery

Frequently asked questions

How much air does a 2.5 in bore cylinder use?

At 90 psig, each inch of extend stroke uses about 35 in³ of free air. A double acting 2.5 × 5/8 in cylinder with a 12 in stroke uses about 0.47 ft³ per cycle before tubing; at 10 cycles per minute, about 4.7 cfm.

Why does retraction use less air?

On retraction air fills only the annulus, the bore area minus the rod area. With a 5/8 in rod in a 2.5 in bore, the annulus is about 94% of the area.

What force margin should I use?

Makers recommend loads up to 70% of theoretical force for horizontal motion and up to 50% for vertical. For 225 lbf at 90 psig and 70%, the minimum bore is about 2.1 in: the next ISO bore is 63 mm (2.48 in).

Does the tube between valve and cylinder count?

Yes. Two 5 ft tubes of 1/4 in ID add about 5.9 in³ per cycle; on small short-stroke cylinders the tubing share can exceed 30%.