Double-acting air cylinders are the work horses of compressed air driven manufacturing equipment. These type of air cylinders are so named because compressed air is used to both extend and retract the rod – a double action.
Single acting air cylinders, on the other hand, use an internal spring or gravity to either extend or retract the cylinder rod.
In this first graphic, a double-acting air cylinder has compressed air entering the cylinder port at the rod-end of the cylinder.
The piston and rod combination are shaded in purple, and the compressed air is shown in blue.
Compressed air has pressurized the inside of the cylinder barrel, and in so doing, has driven the cylinder piston to the rear. The rod, which is attached to the piston, is retracted, and whatever tooling that might be attached to the rod end has been retracted as well.
The air that was in the rear of the cylinder has exited from the rear-cap cylinder port, through the exhaust port in the air valve, and out to atmosphere.
The second graphic shows that the opposite has occurred. Air has entered the rear cylinder cap port, driven the piston to the rod end, and the rod has extended, taking whatever rod end tooling to full rod extension.
Double-acting air cylinders can be manufactured in a repairable cylinder or non-repairable format.
They are usually manufactured to industrial standards including those of the National Fluid Power Association or the European standards ISO-6431 or ISO 6432 .
When selecting a double-acting air cylinder for your application, there are details you will need to clarify:
- How big a diameter or what force is required
- What is the rod length, which translates into how far you wish to move the object
- Does the application require a larger than standard rod and rod bearings
- What size and type of rod end thread is required, and does the application require a male or female thread
- Is position sensing required
- How will the cylinder be mounted
- How will the cylinder rod be connected to the tooling
- What fittings for the cylinder ports
- Will you need flow controls to adjust speed
- Will you need air cylinder cushions
- Will the application require a lubricator, or will the factory lubrication suffice
There are a huge number of manufacturers of double-acting cylinders in the world, most of whom are represented by stocking industrial distributors making this style of air cylinder among the most readily available for original purchase, and for MRO (maintenance, repair & overhaul) replacement.