Electric regulator positioner is the main accessory of control valve.

When the input signal of the electric control valve increases, the moment motor generates electromagnetic field, and the baffle is far away from the nozzle by the electromagnetic field force. The distance between nozzle and baffle becomes larger, eliminating the upper pressure on the axis inside the pilot valve. The affected line axially moves to the right, pushing the valve core blocking the base, and the air pressure is input to the actuator through the base.
With the increase of the internal pressure in the chamber of the actuator of the electric control valve, the push rod of the actuator decreases, and the displacement of the push rod of the actuator is transmitted to the slide plate through the feedback rod. This displacement change is transmitted to the range feedback rod, pulling the range spring. When the force of the range spring and the moment motor is balanced, the baffle returns to its original position and the distance between the baffle and the nozzle is reduced. With the decrease of the amount of air discharged through the nozzle, the upper pressure of the spool increases. When the spool returns to its original position, the valve core re-plugs the base and stops the air pressure input to the actuator. When the motion of the actuator stops, the positioner keeps stable.
Electric regulator valve positioner is the main accessory of control valve. It works according to the principle of moment balance. It takes the displacement of valve stem as the input feedback measurement signal, and the output signal of controller as the setting signal. When there is deviation between the two, it changes the output signal to the actuator.

The one-to-one correspondence between the displacement of the stem and the output signal of the controller is established by the action of the actuator of the electric control valve. Therefore, the valve positioner consists of a feedback control system with the stem displacement as the measurement signal and the controller output as the setting signal. The control variable of the control system is the output signal of the valve positioner to the actuator.