Cylinders are mechanical devices used for translating a pressure medium into a kinetic motion, typically by means of a piston rod. This medium forces the piston to move in whichever direction is required. The piston itself is a cylinder or disc, with the piston rod transferring the mechanical energy of the applied force it develops by means of kinetic energy onto whatever object needs to be moved.
Most pneumatic cylinders with piston rods fall into two or three general categories, although they may vary in size, appearance and function. Single-acting cylinders create their drive force in only one direction and use a spring to return the piston rod to its starting position. This type of pneumatic cylinder is limited by its spring, which takes up space in the cylinder, as well as using up part of the force developed by the piston.
Double-acting cylinders use the driving force of compressed air through two intake ports to move the piston rod in two directions, for both extending and retracting strokes. This kind of cylinder is not limited in stroke length by a spring, but can be more prone to bending and buckling.
Both single and double-acting pistons can be incorporated into a pneumatic telescopic cylinder, which has a piston rod that is nested into a series of hollow telescoping stages. This produces a segmented piston with a noticeably longer stroke, but the piston is more flexible due to its segmented design and can only bear minimal loads.