Three-position pneumatic actuator provides operation mode of 0°-45°-90or0°-90°-180°. The middle position is carried out by two assisting pistons' movement to produce the machinery brake. This position is adjustable, like 90stroke actuator can provide the position of 20°,30°,50°,75°etc positions. In order to control the operation of RP three-position pneumatic actuator, a ser of solenoid valve system which used to control series of air supply pressure actuator is needed according to following description:(the output torque and dimension of three-position double acting stroke actuator should refer to corresponding standard actuator parameter). Position 1(middle position): This position is carried out by the air supply pressure enters into port 2 and port D separately, and the air expel from port 4. As a matter of fact, air pressure supply to the port D and compel the accessory piston move to central, then the handspike that acts as machinery limit makes the inner piston stop at the assigned position. Position 2(wide open position): This position is carried out by the air supply pressure enter into port 2 and port C at the same time(C port may haven't air go through), the air expel from port 4 and port D. In this case, the air pressure expel from the port 2 constantly to make the internal piston to wide open position. Position3 (wide close position): This position is carried out by air supply pressure enter into port 4, and air expel from port 2.