Pneumatic actuators are mechanisms that convert the potential energy of a compressed gas, most frequently air, into mechanical energy to drive a piece of machinery. The compressed gas is directed into a space where its expansion drives a piston or shaft to initiate motion. Types of pneumatic actuators commonly found include single- or double-acting pneumatic cylinders, rotary actuators, and diaphragm actuators. Pneumatic cylinders can also operate based on a rodless design incorporating magnets, bands, or cables.
Cylinder-type pneumatic actuators use a valve to inject compressed gas into a closed chamber with a piston. The expansion of the gas forces the piston down the length of the cylinder. The piston is normally connected to a rod that moves to begin a mechanical operation. Pneumatic cylinders are often used in manufacturing settings such as assembly lines, loading and unloading product, or otherwise aiding the motion control of a process.
A single-acting cylinder uses a spring to return the piston to its starting position. A double-acting cylinder uses two different compressed gas streams, one at each end of the cylinder. One air stream pushes the piston away from the beginning point and the other pushes it back to the other end of the cylinder.
Rotary pneumatic actuators take the potential energy of the compressed gas and convert it into torque, or rotary movement. The actuator drives a rod through an arc, usually between 45 and 180 degrees of rotation. The interior of the actuator may use rotary vanes to create the movement or a rack and pinion configuration. Rotary actuators can operate in a smaller space than a cylinder which requires length for the stroke of the piston.
Another design is a diaphragm pneumatic actuator. In this configuration, a rod is connected to a diaphragm that divides a space into two chambers. Two separate compressed gas streams, one on each side of the diaphragm, create a pressure differential that causes the rod to be forced outward. Many of these actuators are fitted with a spring to return the rod to its original position.
Rodless designs of pneumatic actuators can operate within a shorter length than a rod-type cylinder. The stroke force created by the compressed air is contained within the actuator. The cylinder is supported on slides or bearings to smoothly convey the movement to the process and maintain load support throughout the piston stroke. The movement is controlled with coupled magnets, a sealing band, or cables.