Actuators can be categorized by the energy source they require to generate motion. For example: Pneumatic actuators use compressed air to generate motion. Hydrolic actuators use liquid to generate motion. Electric actuators use an external power source, such as a battery, to generate motion. Thermal actuators use a heat source to generate motion.
The actuators are expected to operate under extreme ambient conditions, however they are generally not used for continuous operation since the motor heat buildup can be excessive. Limit and torque sensors (2) The limit switches signal when an end position has been reached. The torque switching measures the torque present in the valve.
Pneumatic Actuators : A simplified diagram of a pneumatic actuator is shown in Figure 1. It operates by a combination of force created by air and spring force. The actuator positions a control valve by transmitting its motion through the stem. A rubber diaphragm separates the actuator housing into two air chambers.