How Does a Pneumatic Cylinder Work?

A pneumatic cylinder works by directing compressed air against an internal piston. The air pressure creates force across the piston area, moving the piston and the connected piston rod through a controlled stroke.

Extension

During extension, compressed air enters the cylinder and acts against one side of the piston. As pressure builds, the piston moves towards the opposite end of the barrel and the piston rod extends.

Air on the opposite side of the piston is allowed to exhaust through the other port or through the cylinder control valve.

Retraction

In a double acting cylinder, the valve reverses the airflow. Compressed air enters the rod side of the cylinder and moves the piston back towards its original position.

Retraction force is normally lower than extension force because the piston rod occupies part of the effective piston area on the rod side.

Single acting operation

A single acting cylinder uses compressed air for movement in one direction only. An internal spring or an external load returns the piston when the air pressure is removed.

Single acting cylinders can be spring return or spring extend, depending on the required fail position.

How is cylinder speed controlled?

Pneumatic cylinder speed is normally controlled using flow control valves. These regulate how quickly air can enter or leave the cylinder.

In many industrial applications, controlling the exhaust airflow provides smoother and more stable movement than restricting the incoming supply.

What controls the cylinder?

A pneumatic directional control valve determines which cylinder port receives compressed air. The valve may be operated:

• Manually
• Mechanically
• Pneumatically
• Electrically using a solenoid
• Through a PLC or machine control system

What affects cylinder force?

The main factors are:

• Cylinder bore
• Available air pressure
• Piston rod diameter
• Internal friction
• Spring force on a single acting cylinder
• External machine resistance

The theoretical force calculation does not account for every real operating loss. A suitable margin should normally be allowed when selecting a cylinder for an application.

What happens at the end of the stroke?

Many cylinders include mechanical or pneumatic cushioning to reduce the impact of the piston reaching the end cover. Cushioning becomes particularly important with higher speeds, heavier loads and longer strokes.

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