Control Valves, Rotary Actuators, Linear Actuators, Actuators
Actuators can be classified into two types based on their motion. Two primary actuator types are rotary, and linear. An example of a rotary actuator is an electric motor, which is an actuator that converts an electrical signal into a rotating motion of its shaft. Linear actuators, on the other hand, produce a non-rotary motion, such as a sliding motion, or piston motion in response to an input signal. The distinction is somewhat abstract, however, as a linear actuator can be built using a normal rotary motor as its basis, and vice verse. In each case, the initial motion produced is mechanically converted to the other motion-type. Linear actuators can be electrically operated or pneumatic. The pneumatic diaphragm actuator is more popular and used to actuate linear valves such as globe, three-way (diverting or mixing) and angle valves. Pneumatic linear actuators have the simplest construction and provide very precise control of flow.
Rotary actuators, with shafts performing up to 90-degree rotary motion, are mounted on rotary valves such as ball, butterfly, rotary plug and segmented ball valves. These actuators are derived from linear actuators, and use a gearbox or lever system to convert the linear motion into a rotary motion. The actuator construction, where compressed air acts on a rotary vane instead of a piston, has not established itself on the market. The most popular pneumatic rotary actuator is the reciprocating piston cylinder assembly.
In contrast to the pneumatic version of rotary actuators, the rotary motion of electric actuators is inherent. A complex linear unit is needed to transform the rotary motion into a linear stroke.