Three position ALPHA actuator provide an operation of 0°, 45°, 90°or 0° , 90°, 180°.The midway position is achieved by a mechanical stop of movement on the 2 auxiliary pistons. This midway stop positions adjustable. Example:90°actuator can provide 20°, 30°, 40°, 50° , 70°etc. Following is the principle of operation:

1, Fully Closed Position
From chart 1 we can see that this position is obtained when air is supplied to port 4 and port 2 is in the state of exhaust air.

2, Fully Open Position
From chart 2 we can see that this position is obtained when air is supplied to port 2 and port C, meantime, port 4 and port D are in the state of exhaust air.

3, Midway Position
From chart 2 we can see that this position is obtained when air is supplied to port 2 and port D, meantime, port 4 and port C are in the state of exhaust air. In fact that the midway position is achieved by a mechanical stop of movement on the two auxiliary pistons.