What is the function of a positioner?

• A. Uses air to position the valve
• B. Uses electricity to move the stem
• C. Stores energy for actuation
• D. Indicates valve position with lights

Answer: (A)

A positioner is the device that takes a control signal and translates it into the exact air pressure needed to move the valve stem to the commanded position. It continuously compares the desired position from the controller with the actual valve position and modulates compressed air to the actuator to correct any difference. This arrangement allows precise, quick, and stable valve movement and helps the valve maintain the correct position despite changes in load, friction, or supply pressure. Because a pneumatic positioner uses air pressure to drive the actuator, that is why using air to position the valve is the best description of its function. The other ideas describe different components or roles (electric movement, energy storage, or merely indicating position) and don’t capture the corrective, air-driven positioning function of a positioner.