The three-position pneumatic actuator has two models 0° -45° -90° and 0 -90° -180º. The piston will move toward both ends after the air enters from the gas port (2); for the actuator that is fixed with auxiliary pistons for reach the middle position by mechanical limit, you can adjust the middle angle simply using the external adjust丨ngbofts at both ends, such as 20° .30°, 50° and 75° as well as 95° ,120°，130° , 150°and 175° etc.
The operation of the three-position pneumatic actuator is realized based on a set of solenoid-controlled circuit systemr with its controlling principle as follows:
Position 1 (middle position)
When the air supply pressure enters from the gas port 2 and D. the air will be discharged from the gas port 4 and C; the gas port 2 is for internal piston movement while the gas port D is for limiting the internal piston locating it in the prefixed middle position though the auxiliary piston push rod.
Position 2 (fully-open position)
When the air supply pressure enters from the gas port 2 and C. the air will be discharged from the gas port 4 and D; the internal piston at the gas port 2 will continue to move while the gas port C is (or removing limit of the auxiliary piston push rod and making the internal piston reach the fully-open position.
Position 3 (fully-closed position)
When the air supply pressure enters from The gas port 4. the air will be discharged from the gas port 2. and the internal piston will move toward the fully-open position.The spring with resetting model of 0-45-90 i$ available, which is able to compel the internal piston to return to the fully-closed position in case of air or pov/er cut-off (air supply failure).