FIELD OF THE DISCLOSURE

The present disclosure is directed to a gate valve. More particularly, the disclosure is directed to a gate valve which includes a bonnet seal assembly that in some embodiments provides two barriers to the environment in both the open and the closed position of the valve.

BACKGROUND OF THE DISCLOSURE

Prior art gate valves typically include a valve body, a flow bore which extends completely through the valve body, a gate cavity which extends partially through the valve body and intersects the flow bore, and a bonnet which is mounted to the valve body over the gate cavity. The bonnet comprises an axial stem bore within which a valve stem is movably positioned. One end of the valve stem is connected to a valve actuator and the other end is connected to a gate which is positioned in the gate cavity across the flow bore. In operation, the valve stem moves the gate between a closed position in which fluid flow through the flow bore is blocked and an open position in which fluid flow through the flow bore is permitted.

Prior art gate valves normally include a bonnet seal assembly for sealing the stem bore to thereby prevent fluid pressure in the gate cavity from escaping into the environment. Known bonnet seal assemblies typically include a thermoplastic stem packing, such as a UV stem packing, which is positioned between the valve stem and the stem bore. The stem packing provides a primary pressure containing barrier between the gate cavity and the environment.

Prior art bonnet seal assemblies usually also include a secondary sealing arrangement for isolating the stem packing from environmental fluids. Especially when the gate valve is used subsea, such as in the subsea oil and gas production industry, the secondary sealing arrangement prevents ingress of seawater and pressure into the bonnet which could cause the stem packing to fail. For example, certain prior art bonnet seal assemblies include a uni-directional seal that isolates the back of the stem packing from seawater pressure and vents leakage past the stem packing out through a relief valve in the bonnet. The secondary seal arrangement may also serve to isolate the actuator from fluid pressure in the gate cavity should the stem packing fail. For example, certain prior art bonnet seal assemblies include two bi-directional seals to isolate the valve actuator from any leakage past the stem packing.

Certain prior art gate valves are designed to include a metal “backseat” feature to supplement the sealing capability of the bonnet seal assembly. The backseat feature normally comprises a conical shoulder which is formed on the valve stem and a corresponding conical backseat surface which is formed at an end of the stem bore adjacent the gate cavity. When the valve stem is moved into its axially outer position to, e.g., close the gate valve, the shoulder will seal against the backseat surface and form a metal-to-metal barrier between the gate cavity and the stem bore. Thus, the stem packing and the backseat provide “dual barriers” between the gate cavity and the environment.

However, the backseat sealing arrangement is only engaged in one position of the valve stem, usually the closed position. The backseat is not engaged in the open position of the gate valve. In certain applications, the provision of a metal backseat sealing arrangement in both the open and closed positions of the gate valve would be desirable. Together with the stem packing, this would provide dual barriers between the gate cavity and the environment in both the open and closed positions of the gate valve, which would greatly enhance the sealing capability of the gate valve.

SUMMARY OF THE DISCLOSURE

In accordance with the present disclosure, a gate valve is provided which comprises a valve body; a flow bore which extends completely through the valve body; a gate cavity which extends partially through the valve body and intersects the flow bore; a bonnet which is mounted to the valve body over the gate cavity and comprises a stem bore which extends axially therethrough and is connected to the gate cavity; a valve stem which is movably positioned in the stem bore and comprises a first end which extends outwardly of the bonnet and a second end which extends into the gate cavity; a gate which is connected to the second end of the valve stem and is movable by the valve stem between a closed position in which fluid flow through the flow bore is blocked and an open position in which fluid flow through the flow bore is permitted; and a bonnet seal assembly for sealing the stem bore against fluid pressure in the cavity.

The bonnet seal assembly includes a generally cylindrical packing nut which is positioned in the stem bore around the valve stem and comprises first and second spaced-apart annular sealing surfaces which are formed concentrically with the stem bore; a third annular sealing surface which is connected to or formed integrally with the valve stem; and a fourth annular sealing surface which is formed concentrically in the stem bore. In in a first position of the valve stem, the first annular sealing surface sealingly engages the third annular sealing surface to thereby form a first seal to seal the annulus between the valve stem and the packing nut, and the second annular sealing surface sealing engages the fourth annular sealing surface to thereby form a second seal to seal the annulus between the packing nut and the stem bore. In this manner, the first and second seals together operate to seal the stem bore from fluid pressure in the gate cavity. Moreover, the first position of the valve stem corresponds to one of the open position or the closed position of the gate.

In accordance with one aspect of the disclosure, the third annular sealing surface may be formed on an actuator drive stem which is connected to the first end of the valve stem or on an adapter coupling which connects the actuator drive stem to the first end of the valve stem.

In accordance with another aspect of the disclosure, the stem bore may have an enlarged diameter bore portion within which the packing nut is positioned, and the fourth annular sealing surface may be located at an axially inner end of the enlarged diameter bore portion.

In accordance with yet another aspect of the disclosure, the first annular sealing surface may be formed proximate an axially outer end of the packing nut and the second annular sealing surface may be formed proximate an axially inner end of the packing nut.

In accordance with a further aspect of the disclosure, the bonnet seal assembly may further comprise a fifth annular sealing surface which is connected to or formed integrally with the valve stem axially inwardly of the third annular sealing surface, and a sixth annular sealing surface which is formed concentrically in the stem bore axially inwardly of the fourth annular sealing surface. In this embodiment, in a second position of the valve stem, the fifth annular sealing surface sealingly engages the sixth annular sealing surface to thereby form a third seal which operates to seal the stem bore against the fluid pressure in the gate cavity. Also, the second position of the valve stem corresponds to the other of the open position or the closed position of the gate.

In accordance with another aspect of the disclosure, the bonnet seal assembly may further comprise a stem packing which is positioned between the valve stem and the stem bore axially inwardly of the fourth annular sealing surface. In this embodiment, the stem packing provides a pressure containing barrier between the gate cavity and the environment. Thus, in the first position of the valve stem, the stem packing and the first and second seals provide two pressure containing barriers between the gate cavity and the environment, and in the second position of the valve stem, the stem packing and the third seal provide two pressure containing barriers between the gate cavity and the environment.

In accordance with yet another aspect of the disclosure, the bonnet seal assembly may further comprise first and second bi-directional seals which are mounted on the packing nut. In this embodiment, the first bi-directional seal is sealingly engaged between the valve stem and the packing nut and the second bi-directional seal is sealingly engaged between the packing nut and the stem bore.

In accordance with a further aspect of the disclosure, the gate valve may also comprise a pressure bleed port which extends laterally through the bonnet to a portion of the stem bore located between the first and second annular sealing surfaces, and a pressure relief valve which is mounted in the pressure bleed port.

In accordance with still another aspect of the disclosure, the bonnet seal assembly may further comprise a unidirectional seal which is positioned between the stem bore and a portion of the packing nut located between the first and second annular sealing surfaces. In this embodiment, the unidirectional seal is configured to seal against pressure in a portion of the stem bore located axially outwardly of the unidirectional seal.

In accordance with yet another aspect of the disclosure, the packing nut may be axially movably retained in the stem bore. The packing nut may be retained in the stem bore by a retainer nut which is secured to the bonnet axially outwardly of the packing nut. Also, the gate valve may comprise a spring member which is positioned between the retainer nut and the packing nut and is configured to bias the packing nut axially inwardly.

Thus, it may be seen that the bonnet seal assembly of the present disclosure provides backseat seals in both the open and closed positions of the gate valve. In some embodiments, the backseat seals are provided as metal backseat seals. In embodiments in which the bonnet seal assembly also includes a stem packing, the backseat seals, together with the stem packing, provide two pressure containing barriers between the gate cavity and the environment in both the open and closed positions of the gate valve. This greatly enhances the sealing capability of the gate valve.

The gate valve may be configured such that, when the valve is in the open position, the valve actuator imparts a continuous inwardly directed load on the packing nut, thus energizing the first and second backseat seals. In this position, the stem packing provides the primary barrier between the gate cavity and the environment and the first and second backseat seals provide the second barrier between the gate cavity and the environment.

The gate valve may also be configured such that, when the valve is in the closed position, the valve actuator imparts a continuous outwardly directed load on the valve stem, thus energizing the third backseat seal. Fluid pressure in the gate cavity may also contribute to the outwardly directed force on the valve stem. In this position, the third backseat seal provides the primary barrier between the gate cavity and the environment and the stem packing provides the second barrier between the gate cavity and the environment.

When the gate valve is in an intermediate position or the closed position, the volume behind (i.e., outwardly of) the stem packing is in communication, via the uni-directional seal, with the pressure relief valve and can therefore self-vent any pressure build-up behind the stem packing. This feature will prevent trapped pressure from degrading the wear life of the individual seals (which could result in migration of fluid pressure, e.g., from the gate cavity into the actuator), or otherwise impairing the performance of the bonnet seal assembly.

These and other objects and advantages of the present disclosure will be made apparent from the following detailed description, with reference to the accompanying drawings.

