Abstract: A stand-alone electropneumatic closed loop servo system, with a separate gas supply to an air actuated cylinder, provides pressure, position, or fluid flow control of a variable conductivity valve in a device by automatically varying the conductance of the device. The air cylinder defines a control chamber and a smaller volume response chamber separated by a piston operatively connected to the variable conductivity valve. The gas supply includes a constant pressure line, with a pressure regulator valve and a check valve, into the control chamber and a variable pressure line, with a variable pressure solenoid valve, into the response chamber. A feedback signal from the device to a controller is compared to a desired pressure set point. The controller signals the solenoid to vary its output pressure thereby causing the piston to move accordingly to actuate the variable conductance valve.