In ordinary usage people commonly used pneumatic actuators have made the following classification: pneumatic diaphragm actuator and cylinder type actuator, and according to the mode of action is divided into single function and double action, positive interaction (gas off) and reaction (gas open).

We only discuss a single action pneumatic actuators, general pneumatic diaphragm actuator can with reset spring, so are single function, general cylinder type actuator according to have reset spring is divided into single function and double action. In this way, single acting actuators people will match on single acting output valve positioner, double action actuator general with double action locator, this seems to have is natural.

But this concept foreign control valve manufacturer had a breakthrough and successful application, that is to use without spring single-acting pneumatic diaphragm actuator and use belt spring of the double action cylinder actuators, all of them with the double function valve positioner, can make full use of air pressure, realize accurate control, on the one hand, increase output force, on the one hand, provide fail safe mode, and at the same time, using double action locator into exhaust all through the locator and avoid the actuator cavity chamber and the outside air exchange.