Pneumatic rotary actuators use pressurized air to rotate mechanical components. They are used in applications such as machine loading and unloading, material handling, product assembly, welding, packing, testing and quality control. There are several types of pneumatic rotary actuators. Single rack-and-pinion actuators drive a single rack that rotates the pinion. Double or four piston rack-and-pinion actuators drive racks on both sides of the pinion. Single rotary vane devices are actuated directly by pressurized air. Double rotary vane devices use two chambers of pressurized air to produce increased torque. Multi-motion rotary vane actuators are also available. Indexing or multi-position devices allow multiple position stops along strokes. Rotation angle, the angle to which an actuator can rotate before reaching its travel limit, varies widely among pneumatic rotary actuators. Common rotation angles are 45°, 90°, 120°, 135°, 180°, 225°, 270°, 325°, and 360°. Pneumatic rotary actuators with rotation angles less than 45° or greater than 360° are also available.
Specifications for pneumatic rotary actuators include operating pressure range, operating temperature, maximum torque, rotational element type, axial load capacity, radial load capacity, and linear stroke. Operating pressure range and operating temperature are expressed as full-required ranges. Maximum torque, the required range of torque output, if often measured in inch-pounds (in-lbs). Rotational elements for pneumatic rotary actuators include shafts and tables. Shafts are circular and often include a keyway. Single shafts provide outputs on one side of the actuator. Double shafts provide outputs on both sides. Rotating tables often include a bolt pattern for mounting other components. Shaft diameter or table diameter and shaft length or table height are important considerations. With output tables, the height or thickness does not include the actuator body. Axial load and radial load are measured in pounds (lbs). Linear stroke, the distance between the fully retracted and fully extended rod positions, is measured in inches (in).
Selecting pneumatic rotary actuators requires an analysis of product features. Devices with an adjustable angle of rotation can be adjusted via screws or other stop features on one or both ends of the angular stroke. Devices with stop cushioning contain air, a mechanical cushion, or a pad to soften the stop. Pneumatic rotary actuators that provide positional feedback include encoders or potentiometers. Some pneumatic rotary actuators include a closed loop air/oil system for hydraulic-like smoothness. Others surround the output shaft with a magnetic strip or band that can be read by a switch.