A system and method for controlling fluid pressure downstream a main valve includes associating a variable orifice with the main valve such that the variable orifice opens as the main valve is opened and closes as the main valve is closed. A fluid stream taken from a fluid inlet of the main valve is passed to an inlet of the variable orifice. A fixed orifice is in fluid communication with an outlet of the variable orifice. A pressure differential between the inlet and outlet of a fixed orifice is detected by a control pilot device, which hydraulically opens or closes the main valve in response to the detected fixed orifice pressure differential between low pressure and high pressure set points.