How to choose pneumatic actuator

Actuators have sub-electric and pneumatic. To pneumatic, for example, the pneumatic is divided into single role (spring reset) and double role. Pushed by the compressed air screw driven stem rotation. 1. According to the size of the gas source (instrument gas) to select the actuator 2. Torque required to turn the valve, too small to move, too large valve life is not long. Allow 30% of the torque to the general ok ok. 3. Installation platform, there are standards, as long as the valve according to the standard will not find fault.