Why choose a Single Acting Cylinder?

Why choose a Single Acting Cylinder?

What is a single acting cylinder or actuator and why choose one? This article introduces single acting cylinders and advises when you should select single acting over double acting. As the name suggests a single acting cylinder uses air (pneumatic pressure) to drive the piston rod in one direction only; the return action is achieved using a spring.

So, there are two possible rest positions:

• Sprung In, where the piston is fully retracted at rest; and
• Sprung Out, where the piston rod is fully extended at rest

Why choose a single acting cylinder over a double acting cylinder?

There are four principle reasons why a single acting cylinder can be a more effective and/or efficient option:

• Fail safe - where safety may be a critical consideration, the single acting cylinder has a defined rest position in the event of a power failure
• Resets to a known position - the known rest position also makes for an easier reset sequence
• Consumes less air - because air is used in one direction only, there is less consumption compared to a double acting cylinder; this gives optimum efficiency and lower operating cost
• Easier to control - finally, control is relatively simple using a 3/2 way pneumatic valve; air flow from port 1 to port 2 extends (sprung in) or retracts (sprung out) the piston rod and exhausting air from port 2 to port 3 allows the spring to return the piston rod to its rest position.

What are typical applications for single acting cylinders?

Single acting cylinders are ideal where powered motion is required in one direction only:

• Clamping - a work piece can be held in position by jaws operated by the cylinder; a process, such as drilling, can then be carried out, before the spring retracts the jaws
• Positioning - a work piece, or product, can be pushed or pulled into place, for example onto a conveyor belt, before the spring acts and readies the cylinder for the next work piece
• Punching - The thrust from a single acting cylinder can be used to punch or mark an object; the spring then retracts the punch ready for the next object.

It will be noted that a double acting cylinder could be used for all the above applications, but without the benefits already defined.

Visit our Cylinders section to find out more.