Find Your Fit: Single Acting Cylinders Vs. Double Acting Pneumatic Cylinders

For a successful pneumatic system, choosing the right cylinder for your unique industry is essential.

Responsible for converting compressed air into mechanical energy, pneumatic cylinders contribute to powering the pneumatic system. Single and double acting cylinders are two common types of pneumatic cylinders and are responsible for powering a wide variety of industries.

The most popular style of pneumatic actuator consists of a piston and rod moving inside a closed cylinder, designed to move in a straight line to deliver linear motion.

How Does a Pneumatic Cylinder Work?

When looking to specify linear actuators, there are two types of operating principles: single acting and double acting. We will explore these variations, typical applications, and advantages and disadvantages.

Single Acting Cylinders

How Does a Single Acting Cylinder Work?

A single acting cylinder: Parker's P1P Series

A single acting pneumatic cylinder is a cylinder where the thrust or output force is developed in only one direction.

The piston is returned by a fitted spring, or by some other external means such as a weight, mechanical movement, gravity, or an external spring. They have a single port to allow compressed air to enter the cylinder to move the piston to the desired position.

Single acting cylinders are typically used for applications where work is done only in one direction, such as clamping, positioning, marking, stroking and light assembly operations.

There are two types of single acting cylinders:

Advantages

• Simple design

• Compact size

• Reduction in valve and piping costs

• Air consumption is halved compared with the equivalent sized double acting cylinder

Disadvantages

• Return spring side of the cylinder is vented to atmosphere – may allow the ingress of foreign matter, which may lead to malfunctioning and reducing the life of the cylinder.

• Spring operation with extended cylinder life can become inconsistent and provide uncertain end of stroke positions.

• Bore size and stroke of the cylinder is restricted due to limitations of the spring size and force.

• A slight reduction of thrust due to the opposing spring force.

Double Acting Cylinders

How Does a Double Acting Cylinder Work?

A double acting cylinder: Parker's P1F Series

A double acting pneumatic cylinder is one where the thrust, or output force, is developed in both extending and retracting directions.

Double acting cylinders have a port at each end and move the piston forward and back by alternating the port that receives the high-pressure air, necessary when a load must be moved in both directions such as opening and closing a gate.

Double acting cylinders are the most widely used of all designs of linear actuators. They account for approximately 95% of all cylinders used in pneumatic control circuits.

Here's how they work:

Air pressure is applied alternately to the opposite ends of the piston. Application of air pressure produces a thrust in the positive (push) stroke, and a thrust in the negative (pull) stroke.

Double acting pneumatic cylinders are typically used in all applications where the thrusts and stroke lengths required are in excess of those available from single acting cylinders.

Small double acting cylinders are also used for applications where positive end-of-stroke positions are required for both strokes.

Advantages

• Generally, ISO standards are based on the design of double acting cylinders.

• A more extensive range of double acting cylinders than for single acting cylinders, giving many more options of bore and stroke sizes.

• Many variations are available on the basic double acting cylinder design.

Disadvantages

• Cylinders cannot be simply held in a mid-position as the cylinders do not have a mechanism to stay in that position.

• Air is a compressible medium – if a pneumatic cylinder is to be used as a feed cylinder, it has to be coupled to a hydraulic slave cylinder to give a constant feed.

• Long stroke cylinders need adequate guiding of the piston rod to work properly.
  

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