Pneumatic control valve positioners use the flapper/nozzle system. They require compressed air to make everything work correctly and use a signal of 3-15 pounds per square inch to receive the data from the controller. The input tells the bellows to expand or compress, depending on the signal. The bellows move the flapper assembly and the beam that measures the valve stem feedback through the cam.

The working principle of the electro-pneumatic control valve positioner resembles that of the pneumatic control valve positioner. But rather than a pneumatic signal, you get an analog signal, usually 4-20 milliamps. The signal creates an electromotive force (EMF) based on the electrical signal applied to a coil. This force moves the flapper and increases or decreases the air to the valve actuator. You also have feedback from the valve stem and positioner to decrease or increase the output to the valve actuator if needed.

We stock this product in various brands, with varying input/output signals.

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