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The rod, which is attached to the piston, is retracted, and whatever tooling that might be attached to the rod end has been retracted as well.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.
When selecting a double-acting air cylinder for your application, there are details you will need to clarify:
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.