Pneumatics

Know Your Pneumatics: Single or Double Acting? Choosing the Right Cylinder

Know Your Pneumatics: Single or Double Acting? Choosing the Right Cylinder - Bus Doors Opening - Parker Hannifin - Pneumatic Division EuropeThe 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. This style of linear actuator is utilized in a variety of industrial sectors, factory automation and packaging, plus transportation and life science applications.

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

 

Single acting cylinders

A single acting cylinder is one 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.

There are two types of single acting cylinder:

  • ‘Push’ type – where the application of air pressure produces a thrust, thus ‘pushing’ the piston

Know Your Pneumatics: Single or Double Acting? Choosing the Right Cylinder - Single Acting Cylinder Push Type - Parker Hannifin - Pneumatic Division Europe

  • ‘Pull’ type – where the application of air pressure produces a thrust, thus ‘pulling’ the piston

Know Your Pneumatics: Do I need a single or double acting cylinder? - Single Acting Cylinder - Push Type - Parker Hannifin - Pneumatic Division Europe

Know Your Pneumatics: Single or Double Acting? Choosing the Right Cylinder - P1P Single Acting Cylinder - Parker Hannifin - Pneumatic Division Europe

Single acting cylinders, such as Parker's P1P Series, are typically used for applications where work is done only in one direction, such as clamping, positioning, marking, stroking and light assembly operations.

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
  • Slight reduction of thrust due to the opposing spring force

 

Double acting cylinders

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.

Air pressure is applied alternatively 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.
Know Your Pneumatics: Single or Double Acting? Choosing the Right Cylinder - Double Acting Cylinder - Parker Hannifin - Pneumatic Division Europe
Double acting 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.

Know Your Pneumatics: Single or Double Acting? Choosing the Right Cylinder - P1D Double Acting Cylinder - Parker Hannifin - Pneumatic Division EuropeDouble acting cylinders, such as Parker's P1D Series, are the most widely used of all designs of linear actuators. They account for approximately 95% of all cylinders used in pneumatic control circuits.

Advantages:

  • Generally, ISO standards are based on the design of double acting cylinders
  • More extensive range of double acting cylinders than for single acting cylinders, giving many more options of bore and stroke sizes
  • Many variations on the basic double acting cylinder design

Disadvantages:

  • Cannot be simply held in a mid-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

 

Learn more

Discover the 6 steps to specifying linear actuators in our blog Know Your Pneumatics: Specifying Linear Actuators.

 

Know Your Pneumatics: Single Acting vs Double Acting Cylinders - Kevin Hill, European Product Manager Pneumatic Actuators - Parker Hannifin - Pneumatic Division EuropeArticle contributed by Kevin Hill, European product manager pneumatic actuators, Pneumatic Division Europe, Parker Hannifin Corporation.

 

 

 

 

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