Single Acting Vs Double Acting Pneumatic Cylinders

In single-acting cylinders, pressurised air enters through only one intake port, while in double-acting cylinders, the compressed air enters through two opposing ports. This means the double-acting cylinder is driven in both directions under pressure, whereas the single-acting cylinder’s return is effected by mechanical means. These simple factors have a major bearing on the movement and speed of your cylinder. 

Choosing between single-acting and double-acting pneumatic cylinders depends not only on the number of its intake ports, but on other factors such as your specific application specs and how much force and motion you’ll need. When choosing between the two types of pneumatic cylinders, it helps to know how they differ and what their advantages and disadvantages are. Then you’ll be in a better position to decide how each device will best match your application requirements.

Pneumatic Cylinders: General Operating Principle

The general operating principle of pneumatics is to convert static energy into kinetic energy. In a pneumatic actuator, this means applying the power of compressed air to move a mechanical object, creating linear or sometimes circular motion. If you connect a compressed air supply to a pneumatic cylinder at one end, the force of the air pressure pushes the piston rod inside it to move in a linear fashion. When this is connected to a machine application, it drives the mechanical action. 

You can control the piston rod's movement with a number of valves, which regulate the flow of compressed air into and out of the cylinder. The size, shape and fabric of your cylinder have a direct effect on its operational efficiency and accuracy, together with the compressed air’s pressure and flow rates. 

Single-Acting Pneumatic Cylinders

A single-acting pneumatic cylinder works on the principle of unidirectional power. You attach the compressed air supply to the intake port at one end of the cylinder, and its pressure causes the piston to extend its rod to the other end. There, it will encounter and compress a spring-loaded return mechanism, or some other external load. When you shut off the compressed air supply, the compressed air is exhausted and the spring forces the piston to retract its rod and return to its original position.

Single-Acting Cylinders come in two different varieties: 

• The push type, where the compressed air pushes the piston out

• The pull type, where the compressed air pulls the piston into the cylinder

Some Advantages and Disadvantages of Single-Acting Pneumatic Cylinders

Advantages

• When you require only unidirectional motion, single-acting cylinders are usually cheaper to buy and more cost-effective to run.

• Their design is simple, with a smaller housing and fewer ports, so they’re easy to install.

• Single-acting cylinders typically require less air pressure, so you save on power, as well as on valve and piping costs.

• They’re safer to operate. The spring returns the piston automatically to its start position if there’s any loss of air pressure.

Disadvantages

• A lower level of precision and control.

• Less drive power to the piston rod as the return spring offers resistance.

• The spring mechanism takes up too much space, so the working area is limited.

• Springs are prone to failure and deterioration, leading to inconsistent piston strokes.

Common Applications for Single-Acting Pneumatic Cylinders

• Clamping parts or components in place while they’re shaped, drilled or cut.

• Ejecting finished parts from moulds or conveyor belts.

• Lifting loads with machinery such as vehicle jacks or pneumatic lifts.

Double-Acting Pneumatic Cylinder

Double-acting pneumatic cylinders use compressed air intake ports at both ends of the piston, so the piston moves in both directions under pressure. You control the airflow to each port with a system of pneumatic valves. Double-acting cylinders are useful for machines requiring powered motion in more than one direction. They need no spring to extend and retract the piston, so they involve fewer mechanical parts. They’re used more widely than single-acting cylinders because piston movement is faster, rendering them more efficient and precise. 

Advantages and Disadvantages of Double-Acting Pneumatic Cylinders

Advantages

• More precise motion control since pressurised air moves the piston both ways.

• Stronger, faster, and more energy-efficient. 

• Greater reliability, as they’re not dependent on the spring return mechanism. 

• Greater design variation with a wide range of stroke and bore sizes.

• More likely than single-acting pneumatic cylinders to be ISO compliant.

Disadvantages

• They can be more expensive than single pneumatic cylinders as they require more compressed air.

• Compressed air consumption is sometimes calculated at different rates. 

• They need a larger housing, and may have to be coupled with another machine system if you use them as feed cylinders.

Common Applications for Double-Acting Pneumatic Cylinders

You’d likely choose double-acting pneumatic cylinders for applications demanding precise control of force and motion, such as:

• Robotic applications, where precision control is essential for robotic arms and delicate components.

• Material handling applications, such as lifting equipment or conveyor systems, where their precision control provides safe and efficient operation.

• Machine tools like lathes or milling machines, where precision control allows for accurate and efficient machining.

Single-Acting vs Double-Acting Cylinders: Which One Should You Choose?

Although you use compressed air to drive both systems, they perform quite differently. You’ll likely choose single-acting cylinders for light assembly work or industrial applications requiring only unidirectional force. If your applications demand higher force, efficiency and speed, you’ll probably opt for double-acting cylinders. 

Your budget is also going to be a factor when considering the initial purchase price against the costs of maintenance. Single-acting cylinders are typically cheaper and easier to install, but require more maintenance. Double-acting cylinders offer faster, stronger and more efficient performance, and their superior design usually justifies the higher initial cost.