Valve Positioner

What is a Valve Positioner?

As a common control valve accessory, the valve positioner delivers pressurized air to the valve actuator so that the position of the valve stem or shaft corresponds to the set point from the control system. Valve positioners are typically pneumatic or analog I/P and are used when a valve requires throttling action. They require position feedback from the valve stem or shaft and deliver pneumatic pressure to the actuator to open and close the valve

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How It Works

Pneumatic Valve Positioners

Legacy processing units may use pneumatic pressure signaling as the control set point to the control valves. In a common pneumatic positioner design, a pneumatic input signal is received from a control device and modulates the supply pressure to the control valve actuator, providing an accurate valve stem or shaft position that is proportional to the pneumatic input signal.

Analog I/P Valve Positioners

Most modern processing units use a 4 to 20 mA DC signal to modulate control valves. This introduces electronics into the positioner design and requires that the positioner convert the electronic current signal into a pneumatic pressure signal (current-to-pneumatic or I/P). In a typical analog I/P positioner, the converter receives a DC input signal and provides a proportional pneumatic output signal through a nozzle/flapper arrangement. The pneumatic output signal provides the input signal to the pneumatic positioner.

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Control Valves & Accessories Handbook

A helpful resource on a variety of valve topics, including positioner basics and how they can benefit your process.

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