This invention relates generally to a regulator valve which incorporates a diaphragm to control the flow of fluid through the valve and diaphragm support means for preventing rupture of the diaphragm.
It is well known in the art that a regulator valve may incorporate a deformable elastomeric diaphragm that is used to control the magnitude of fluid flow through the valve. Such valves are disclosed in U.S. Pat. No. 4,624,442, entitled "Control Regulator Having a Rolling Diaphragm, and U.S. Pat. No. 4,619,436, entitled "Control Regulator Having a Fabric Reinforced Diaphragm," both of which are assigned to Fisher Controls International, Inc. and are incorporated herein by reference. To control the flow in such a valve, the diaphragm is controllably deformed, or moved, so that it selectively covers or uncovers a plurality of apertures in a baffle positioned between an upstream fluid inlet and a downstream fluid outlet. The extent to which the apertures are covered by the diaphragm determines the flow rate through the baffle, and thus the valve.
The movement of the diaphragm, and thus the flow rate through the valve, may be controlled by a pilot pressure supplied to a control chamber in fluid communication with one side of the diaphragm. The pilot pressure may be based upon the difference between the fluid inlet and outlet pressures. A diaphragm support element may be included in the control chamber to provide a surface against which the diaphragm may abut to help control its movement.
It is possible for the above-described valves to be improperly used under certain circumstances, such as during "startup." Prior to startup, a regulator valve may be fluidly isolated from the pipeline or conduit to which it is attached by three shutoff valves: an upstream shutoff valve fluidly coupled to the regulator valve inlet, a downstream shutoff valve coupled to the regulator valve outlet, and a pilot shutoff valve. During startup, these three shutoff valves are opened to fluidly couple the regulator valve to the pipeline. During the startup procedure, the inlet shutoff valve should be opened prior to the opening of the pilot shutoff valve. Opening those two valves in that sequence will temporarily cause a relatively large pressure differential across the diaphragm. That pressure differential, although it may be several hundred pounds per square inch (psi), will not rupture the diaphragm because the diaphragm will be supported by the diaphragm support element in the control chamber of the regulator valve.
However, if the fluid inlet and pilot shutoff valves are opened in the wrong sequence during startup, with the pilot shutoff valve being opened first, a relatively large differential pressure may be exerted across the diaphragm in the opposite direction, in which case the resultant force may cause the diaphragm to rupture. The consequences of diaphragm rupture can be serious, causing at least the delay and expense of replacing the diaphragm and perhaps safety hazards or environmental damage.