Air cylinders are pneumatic linear actuators driven by pressure differential in the cylinder chambers. Compressed gas (typically air) acts as the power to impart a force and cause actuation. The compressed gas is allowed to expand due to the pressure gradient, and forces a piston to move in the desired direction. One side of a piston flange can be pressurized to provide force and motion with a spring (providing return force after pressure is released), or both sides can be alternately pressurized for bi-directional powered motion.

Air cylinders are used in applications which push, pull, and lift objects, close doors, or hold, remove, and position parts. They are commonly used in materials handling and processing. Air cylinders are also important in fail safe systems.Image Credit --SMC Controls.