The Posi-flate Model 7000 positioner causes rotation of a valve actuator in proportion to an input signal. The spool shifts and a differential pressure is created across the actuator, causing rotation. Rotation is fed back through the positioner shaft and cam. Cam rotation causes rotation of both follower arm and feedback arm about their respective pivot pins. Rotation of feedback arm changes compression in the feedback spring which forces the balance beam and spool back to their neutral positions. This shuts off the flow of air to the actuator.

Zero adjustment is made by varying spring compression via a screw in the feedback arm. Span adjustment is made by moving the point of contact between the follower arm and feedback arm via a carriage assembly featuring rack-and-pinion adjustment. Since both arms are parallel at zero, span adjustment does not affect zero setting.

When used on a Posi-flate butterfly valve as shown, the positioner is enhanced with the addition of controls which automatically inflate and deflate the seat. Once the disc is in the fully closed position, the seat is automatically inflated. When the positioner is energized to open, the seat deflates and the disc opens.