Valve positioners compare a control signal to a valve actuator’s position and move the actuator accordingly. They are used with both linear valves and rotary valves. Valve positioners are used when the 0.2 to 1 bar pressure in the diaphragm chamber is not able to cope with friction and high differential pressures.
The positioner is fitted to the yoke of the actuator and is linked to the spindle of the actuator by a feedback arm in order to monitor valve position. When a control signal differs from the valve actuator’s position, the valve positioner sends the necessary power to move the actuator until the correct position is reached. This uses a high air supply. Positioners should be installed if the valve is intended for use in a control application.