A pressure control system for controlling the pressure of a process fluid stream at a certain location having a pressure regulator disposed in the process fluid stream, through which the process fluid stream flows. In certain embodiments, an air column follows a tortuous path between a mouthpiece, having an input orifice between about one to about one-and-one-half inches in diameter, and an exit port. When power-off, the first input terminal of the switch is connected to a reference voltage, and the output terminal of the output network provides an operating DC bias which is gradually reduced.