Patent ID: 6866061

Claim:
A back pressure valve, comprising: (a) a first housing including a first chamber formed therein having a fluid inlet and a fluid outlet for a first fluid, the fluid outlet being an outlet of the back pressure valve; (b) a second housing including a second chamber formed therein; (c) a flexible diaphragm having an outer peripheral edge portion abutting the second housing and closing off the second chamber; (d) a back pressure member moveably disposed in the first chamber of the first housing for controlling fluid flow between the fluid inlet and the fluid outlet, wherein the first chamber is defined by the first housing and the back pressure member; and wherein the flexible diaphragm is fixed onto and moveable together with the back pressure member, whereby pressure in the second chamber determines fluid pressure required to maintain the back pressure member in a steady position; (e) a reference inlet and a reference outlet, for a reference fluid, provide in the second housing, and a control valve means in the second housing connected to the reference inlet and the reference outlet, for controlling the pressure in at least part of the second housing applied to the flexible diaphragm and the back pressure member; wherein the back pressure member is moveable to a closed position in which the back pressure member seals off fluid flow between the fluid inlet and the fluid outlet; wherein the first chamber includes a bore, wherein the fluid inlet and the fluid outlet open into the bore, and wherein the back pressure member is slidably mounted in the bore for movement within the bore; wherein the back pressure valve further comprises a sleeve member disposed within the first housing and providing said bore for the back pressure member, the sleeve member being fixed to the first housing and having a lower opening that is closed by the back pressure member in the closed position and that permits fluid to flow from the fluid inlet to the fluid outlet when the back pressure member is in an open position: wherein the back pressure member comprises a valve plug disposed substantially within the sleeve member; and wherein the back pressure member further comprises an annular seat member disposed at a lower end thereof, whereby, when the back pressure member is in the closed position, the annular seat member abuts a circular shoulder of the sleeve member to thereby close said lower opening.