Shut-off trim including spring loaded check valve
In accordance with the present invention, there is provided a bi-directional shut-off trim for a valve which possesses the functional attributes of a pilot operated trim and a balanced trim through the integration of a spring loaded check valve into a pilot trim. In forward flow isolation, the bi-directional shut-off trim of the present invention acts as a normal pilot operated trim. In reverse flow, the check valve of the shut-off trim opens to balance the pressure on either side of the plug thereof.
1. A valve for regulating the flow of a fluid, the valve comprising:
a housing which includes an interior plug chamber, inflow and outflow passages which fluidly communicate with the plug chamber, and a seating surface disposed between the plug chamber and the outflow passage;
a reciprocally movable valve stem which extends into the plug chamber and defines a stem sealing surface; and
a shut-off trim disposed within the plug chamber between the inflow and outflow passages, the shut-off trim comprising:
a main pilot plug having a bore extending axially therethrough, the main pilot plug defining a main sealing surface, and a stem seating surface which is disposed within the bore thereof;
a plug plate attached to the main pilot plug and including at least one flow opening disposed therein which facilitates the fluid communication between the interior plug chamber and the bore of the main pilot plug; and
a check valve assembly which is disposed within the main pilot plug and fluidly communicates with the bore and the plug chamber;
the shut-off trim being reciprocally movable between a closed position wherein the main sealing surface of the main pilot plug is sealed against the seating surface of the housing and the stem sealing surface of the stem is sealed against the plug seating surface of the main pilot plug, and an open position wherein the main sealing surface of the main pilot plug is separated from the seating surface of the housing and the stem sealing surface of the stem is separated from the plug seating surface of the main pilot plug, the shut-off trim being configured such that the separation of the stem sealing surface from the plug seating surface occurs prior to the separation of the main sealing surface from the seating surface as the shut off trim moves from the closed position toward the open position, the stem acting against the plug plate to facilitate the separation of the main sealing surface of the main pilot plug from the seating surface.
2. The valve of claim 1 wherein the valve stem is sized and configured relative to the main pilot plug such that:
the movement of the stem in a first direction when the shut-off trim is in the closed position initially facilitates the separation of the stem sealing surface thereof from the plug seating surface, the stem thereafter acting against the plug plate in a manner facilitating the separation of the main sealing surface of the main pilot plug from the seating surface; and
the movement of the stem in a second direction opposite the first direction when the shut-off trim is in the open position causes the stem to act against the main pilot plug in a manner facilitating the sealed engagement between the main sealing surface thereof and the seating surface.
3. The valve of claim 2 wherein the check valve assembly is sized and configured to normally block direct fluid communication between the bore and the plug chamber when the shut-off trim is in the closed position.