Valve positioner is a device used to place the valve in the correct position by increasing or reducing the air load pressure on the actuator. Instead of the process controller sending signals directly to the actuator to move the valve, the valve positioner senses the exact position of the valve and communicates with the actuator to move the valve. Valve positioners are usually installed on the egg yolk or top shell of pneumatic actuators (for linear control valves) or near the shaft end (for rotary control valves). Either setting, the positioner is mechanically connected to the stem or stem. This compares the position of the valve with the position required by the controller.