Patent ID: 8550101

Claim:
A method of controlling fluid pressure downstream from a main valve, comprising the steps of: providing a main valve having a fluid inlet and a fluid outlet, the main valve being configured to open to increase fluid flow therethrough, and close to reduce fluid flow therethrough; associating a variable orifice with the main valve such that the flow area of the variable orifice changes as the main valve position changes; setting an upper pressure set point while selectively limiting a range of travel of a high pressure diaphragm of a control pilot valve apparatus, and setting a lower pressure set point by selectively limiting a range of travel of a low pressure flexible diaphragm of the control pilot valve apparatus; passing a fluid stream, having a pressure proportional to a fluid inlet pressure of the main valve, to an inlet of the variable orifice; placing a fixed orifice within a pilot control system associated with the main valve such that an inlet of the fixed orifice is in fluid communication with an outlet of the variable orifice; detecting a pressure differential between the inlet and an outlet of the fixed orifice; and hydraulically opening or closing the main valve in response to the detected fixed orifice pressure differential; using the control pilot valve apparatus, in fluid communication with the variable orifice, the fixed orifice, and the main valve, to detect the pressure differential between the inlet and outlet of the fixed orifice and open or close the main valve.