Air cylinders are the final component in a pneumatic or compressed air control or power system. Air cylinders, or pneumatic cylinders, are devices that convert compressed air power into mechanical energy. This mechanical energy produces linear or rotary motion. In this way, the air cylinder functions as the actuator in the pneumatic system, so it is also known as a pneumatic linear actuator. The air cylinder consists of a steel or stainless steel piston, a piston rod, a cylinder barrel and end covers. As compressed air moves into a cylinder, it pushes the piston along the length of the cylinder. Compressed air or a spring, located at the rod end of the cylinder, pushes the piston back. Valves control the flow of compressed air to the cylinder. The choices for cylinder housing styles include the following: tie-rod, smooth body, pancake, rectangular, multiple bore, stainless steel, rodless, compact, miniature/microcylinder, clean profile and twin-rod cylinder.