What is a Pneumatic Cylinder and How Does It Work?

Pneumatic cylinders are the muscle of compressed air systems. They convert air pressure into linear mechanical force, powering everything from simple clamps on a production line to complex multi-axis automation cells. Understanding how they work and what types are available will help you select the right actuator for any application.

How a Pneumatic Cylinder Works

At its core, a pneumatic cylinder is a sealed chamber with a piston inside. Compressed air is admitted to one side of the piston, creating a pressure differential that pushes the piston — and the rod attached to it — along the bore of the cylinder.

The force produced is determined by the piston area and the air pressure: Force (N) = Pressure (bar) × Bore Area (cm²) × 10. A cylinder with a 50mm bore at 6 bar produces approximately 1,178N (about 120kg) of thrust on the advance stroke.

Single-Acting vs Double-Acting Cylinders

This is the most fundamental distinction in pneumatic cylinder types:

Single-acting cylinders have one air port. Compressed air advances the piston; a return spring retracts it when the air is exhausted. They are compact and require only a 3/2 directional control valve, but the spring reduces effective thrust and limits stroke length.

Double-acting cylinders have two air ports — one at each end of the bore. Air alternately pressurises each side while the other exhausts, giving powered movement in both directions. Double-acting cylinders deliver more consistent force, longer strokes and faster cycle rates. They require a 5/2 directional control valve.

Cylinder Bore and Stroke

The bore is the internal diameter of the cylinder body, which determines the force output. The stroke is how far the piston travels. Standard bore sizes range from 12mm to 320mm in the ISO 15552 range, with strokes from 10mm to several metres on special-build cylinders.

When specifying a cylinder, you need to know the required force (to select bore), the required travel distance (to select stroke), and the mounting configuration (to match the machine structure).

ISO 15552 and Compact Cylinders

ISO 15552 (formerly ISO 6431 and VDMA 24562) is the standard profile cylinder used in the vast majority of industrial machinery. The standardised dimensions mean that cylinders from different manufacturers are interchangeable. This is the first type to consider for any general-purpose linear motion requirement.

Compact (short-stroke) cylinders to ISO 21287 are used where installation space is limited. They sacrifice stroke length for a much shorter overall body length. Typical strokes are 5mm to 100mm.

Round cylinders (ISO 6432) are smaller diameter cylinders for light-duty work in space-constrained locations.

Cushioning and End-of-Stroke Control

At high speeds, a piston reaching the end of its stroke creates a significant impact. Most ISO 15552 cylinders include adjustable pneumatic cushioning — air trapped in a cushion chamber decelerates the piston smoothly before it reaches the end cap, reducing noise and mechanical stress.

Key Selection Criteria

1. Required force — calculate from the load plus any friction allowance (typically add 25%)
2. Stroke length — measure the required travel with a margin for adjustment
3. Mounting style — foot, flange, pivot, rod clevis or tie-rod variations
4. Operating environment — stainless steel or coated cylinders for washdown, high-temperature seals for elevated temperatures
5. Speed — controlled by flow control valves on the exhaust ports

Parker is one of the world’s leading manufacturers of pneumatic cylinders, offering the full ISO 15552 range alongside compact and specialty actuators. Browse our Parker pneumatic cylinders and actuators for specifications and pricing.

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