Pneumatic Cylinders and Their Types

Pneumatic cylinders are used to produce linear and angular motion. They convert pneumatic energy into mechanical energy. There’s a wide variety of standard and non-standard cylinder types. Cylinders manufactured for general applications can withstand working pressures of up to 10 bar. For higher pressures, specially manufactured pneumatic cylinders should be used.

Types of Pneumatic Cylinders and Their Symbols

Single-Acting Cylinders

Single-acting cylinders can only do work in one direction. Motion in the other direction is provided by a spring force, the piston rod’s own weight, or an external force. They’re used for tasks such as clamping, lifting, and tensioning.

These cylinders consume less air and are cheaper to manufacture. Their stroke lengths are generally short. For this reason, they’re not commonly used for strokes longer than 100 mm. Since work is done against a spring, there’s an energy loss of about 20%.

In spring-return cylinders, part of the force generated is spent overcoming the spring force. If a spring outside the cylinder is used to return the cylinder, this type of cylinder is called weight-return (gravity-return).

The cylinder has a single air inlet port. The port on the other side allows air to flow in and out of the cylinder during motion. To prevent contamination, this port is covered with a filter.

Controlling a Single-Acting Cylinder with a 3/2 Valve

In the example circuit, when the 3/2 valve is triggered, ports 1 (supply) and 2 (to actuator) are connected, and the cylinder extends. For the return stroke, the directional valve must be returned to its original position.

The required force is provided by the spring, and the air remaining on the extend side is exhausted through the valve’s exhaust port.

Double-Acting Cylinders

A double-acting cylinder’s motion in both directions is provided by compressed air. This is the most widely used type of cylinder in pneumatic systems. This type of cylinder can do work both extending and retracting. Their stroke lengths are longer than single-acting cylinders.

There are two different surfaces that compressed air acts on. As a result, double-acting cylinders achieve two different speeds and forces on the extend and retract strokes.

Controlling a Double-Acting Cylinder with a 5/2 Valve

Because a double-acting cylinder’s motion requires compressed air in both directions, the valve used needs to pressurize one side while exhausting the air on the other side.

For this reason, double-acting cylinders are normally controlled with 5/2 (5-Port/2-Position) valves

Controlling a Double-Acting Cylinder with a 5/2 Valve

In the starting position, the cylinder is retracted, and while the retract side is under pressure, the extend side is open to atmosphere through the exhaust port.

When the valve’s position is switched, the compressed air at port 1 is routed to the extend side through port 4, and at the same time, port 2 opens to port 3, exhausting the air on the retract side. In this state, the cylinder extends. When the valve is returned to its original position, the sequence of motion reverses, and the cylinder returns to its starting position.

Tandem Cylinders

This type of cylinder is used to achieve high thrust forces. It’s made up of two or more cylinders with equal strokes joined end to end. The number of ports and the thrust force increase depending on the number of cylinders. To reduce air consumption when returning a tandem cylinder to its retracted position, it’s enough to send air to just one of the cylinders.

Thanks to tandem cylinders, a cylinder’s thrust force can be significantly increased without needing to increase the cylinder’s bore diameter or pressure.

Telescopic Cylinders

These cylinders consist of nested cylinders of different diameters. They’re used in places where a long stroke is needed but excessive space isn’t available. They’re used much more in hydraulic systems than in pneumatic systems. The effective surface area during the initial extend motion is small, so low forces are obtained.

Rotary Cylinders

These are used to obtain angular motion. They’re used for angular motion needed in places such as rotary tables, opening and closing large valves, robots, etc. Industrial applications generally need angular motion in increments of 90°. The most commonly used angular motion is 180°.