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العربيةSingle Acting Pneumatic Cylinders
A single acting pneumatic cylinder uses compressed air to move the piston in one direction only; a built-in spring, or the load itself, moves it back when the air is exhausted. It needs a single air port and a 3/2 valve and uses about half the air of a double acting cylinder, but the spring shortens the practical stroke and reduces the output force.
Fenitsa builds spring-return versions on request on the bodies of its pneumatic cylinder ranges — ISO 15552 and CETOP, Ø32–Ø100 mm. This page explains how they work, how to calculate the net force and when a double acting cylinder is the better choice.
How a Single Acting Air Cylinder Works
Air enters through the single port in the rear cap and acts on the full piston area. The piston travels forward, pushes the rod out and compresses the return spring. When the valve switches, the port is connected to exhaust, the pressure falls and the spring drives the piston back to its rest position.
The opposite chamber is not pressurised. It breathes to atmosphere through a small vent, which is why a filter or silencer on the vent is worth fitting in dusty or wet areas — otherwise the cylinder draws dirt in on every return stroke.
Because only one side is powered, the working stroke has the full air force minus the spring, while the return stroke has only the spring force. Speed and force on the return cannot be adjusted with air pressure.
- Rear cap (cap end)
- Rear clevis mounting
- Port A — cap end (full bore side)
- Barrel (cylinder tube)
- Tie rods and nuts
- Piston
- Piston seal
- Wear (guide) rings
- Piston rod
- Front head (gland)
- Rod bearing (guide bush)
- Rod seal
- Wiper (scraper)
- Breather (vent) — rod side open to air
- Cushioning spear and adjusting screw
- Static O-rings
- Rod eye
- Return spring
Cap-side chamber — pressure acts on the full piston area
Spring Return, Spring Extend and Load Return
Three ways to make the piston come back.
| Type | Rest position | Air does | Typical job |
|---|---|---|---|
| Spring return (push type) | Rod retracted | Extends the rod against the spring | Clamping, ejecting, pushing parts off a conveyor |
| Spring extend (pull type) | Rod extended | Retracts the rod against the spring | Stops and locks that must stay closed when the air is off |
| Load return (no spring) | Depends on the load | Lifts or pushes; the load returns the piston | Vertical lifting of light loads where gravity lowers the rod |
Spring return is the most common version. Spring extend is chosen when the safe position is “rod out”. A load-return design has no spring at all, so it keeps the full air force, but it only works where the load reliably pushes the piston back.
Force Formula: Air Force Minus Spring Force
Fnet = p × A − FspringA = π × D² / 4With pressure p in bar and bore D in mm, the air force in newtons is p × 0.1 × A (A in mm²). The spring force is not constant: it is lowest at the start of the stroke and highest at the end, where the spring is most compressed. Size the cylinder so that the net force at the end of the working stroke still does the job, then add a margin of 1.5 to 2 for dynamic loads and friction.
Spring force depends on the spring chosen for the stroke, so it is stated in the quotation for your cylinder rather than in a general table. The table below gives the theoretical air force before the spring is subtracted.
| Bore | Piston area (cm²) | N at 4 bar | N at 6 bar | N at 8 bar | lbf at 6 bar (87 psi) |
|---|---|---|---|---|---|
| Ø32 mm | 8.04 | 322 | 483 | 643 | 108 |
| Ø40 mm | 12.57 | 503 | 754 | 1,005 | 170 |
| Ø50 mm | 19.63 | 785 | 1,178 | 1,571 | 265 |
| Ø63 mm | 31.17 | 1,247 | 1,870 | 2,494 | 420 |
| Ø80 mm | 50.27 | 2,011 | 3,016 | 4,021 | 678 |
| Ø100 mm | 78.54 | 3,142 | 4,712 | 6,283 | 1,059 |
For push and pull values of any bore and pressure, use the pneumatic cylinder force calculator.
Air Consumption
Free air per working stroke, 100 mm stroke at 6 bar.
| Bore | Litres per cycle | L/min at 10 cycles/min |
|---|---|---|
| Ø32 mm | 0.56 | 5.6 |
| Ø40 mm | 0.87 | 8.7 |
| Ø50 mm | 1.36 | 13.6 |
| Ø63 mm | 2.16 | 21.6 |
| Ø80 mm | 3.48 | 34.8 |
| Ø100 mm | 5.44 | 54.4 |
Air consumption per cycle ≈ A × stroke × (p + 1.013) / 1.013. A single acting cylinder fills only one chamber per cycle, so it uses about half the air of a double acting cylinder of the same size. Scale the values linearly for other strokes and cycle rates; hoses and valve volume add a little on top.
Where Single Acting Cylinders Make Sense
Clamping and holding
Short, repeated clamping strokes in fixtures; the spring releases the part if the air is lost.
Ejecting and pushing
Pushing parts off a conveyor or out of a tool, where the return stroke carries no load.
Stops, gates and locks
Spring-extend versions keep a stop closed until air is applied — a fail-safe rest position.
Light lifting
Load-return cylinders lift a light load and let gravity bring it down.
Single vs Double Acting Pneumatic Cylinders
| Single acting | Double acting | |
|---|---|---|
| Air ports | One (plus a vent) | Two |
| Valve | 3/2 | 5/2 or 5/3 |
| Return stroke | Spring or load | Compressed air |
| Force on the return | Spring force only | Full pull force (piston area minus rod area) |
| Usable stroke | Short — limited by the spring | Long strokes possible |
| Air consumption | About half | Both chambers filled every cycle |
| Position on air failure | Defined by the spring | Stays where it is (unless valve logic moves it) |
| Speed control | Working stroke only | Both directions |
All standard Fenitsa catalogue cylinders are double acting; see double acting pneumatic cylinders for the full force table from Ø32 to Ø320 mm.
What to Tell Us When You Order
- Bore and strokeCylinder bore and working stroke in mm.
- Force at the end of the strokeThe net force you need after the spring, and the working pressure available.
- Spring return or spring extendWhich rest position the machine needs when the air is off.
- Mounting and rod endRear clevis, flange, foot or trunnion; rod clevis or spherical rod end.
- EnvironmentTemperature and contamination. PU seals cover −20 °C to +80 °C; Viton seals are available for higher temperatures.
- QuantityOne-off or series, and the delivery schedule.
Send Us Your Cylinder Data
Bore, rod, stroke, working pressure, mountings and quantity — or a drawing or photo of the cylinder you want to replace. Our engineers reply with a technical proposal and a quotation. info@fenitsa.com.
Single Acting Pneumatic Cylinder – FAQ
Short answers from our engineers.
What is a single acting pneumatic cylinder?
An air cylinder that is powered in one direction only. Compressed air extends (or retracts) the piston, and a spring or the external load moves it back when the air is exhausted.
Which valve does a single acting cylinder need?
A 3/2 directional valve: one position supplies air to the single port, the other exhausts it so the spring can return the piston. A double acting cylinder needs a 5/2 or 5/3 valve instead.
How do you calculate the force of a single acting cylinder?
Take the air force, F = p × A, and subtract the spring force. Because the spring force grows as it is compressed, check the net force at the end of the working stroke, where it is lowest.
What happens if the air supply fails?
The spring returns the piston to its rest position. That is why spring-return cylinders are chosen for clamps, stops and locks that must go to a known position when the air is lost.
Can a single acting pneumatic cylinder have a long stroke?
Usually not. The compressed spring takes up length inside the cylinder and its force rises with stroke, so single acting designs are kept short. For long strokes a double acting cylinder is the practical choice.
Do single acting cylinders use less air?
Yes. Air is used only for the working stroke, so consumption is roughly half that of a double acting cylinder of the same bore and stroke.
Related Pages
Double Acting Pneumatic Cylinders
Push and pull force Ø32–Ø320 mm at 6 bar.
ISO 15552 Cylinder FMY (Ø32–Ø100)
Magnetic piston, adjustable cushioning, ISO mountings.
Single Acting Hydraulic Cylinders
The same principle with oil at 160 bar.
Pneumatic Cylinder Force Calculator
Force in N, kgf and lbf for any bore and pressure.