A flow control valve (FCV) controls the flow of liquids, gases, and air. By pneumatically adjusting the position of a needle valve on the seat, the Proportion-Air FCV valve flow control valve goes above and beyond that. Using a companion driver unit, an external PID controller regulates the flow control valves in the FCV-M series. The PID controller uses a 4-20 mA or DC signal to control and continually monitor valve position.