Gate valve with improved bonnet seal assembly

1. A gate valve comprising:

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, the bonnet comprising 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, the valve stem comprising a first end and an opposite second end which extends into the gate cavity;

a gate which is connected to the second end of the valve stem, the gate being 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 comprising:

a generally cylindrical packing nut which is positioned in the stem bore around the valve stem, the packing nut comprising 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 is configured to sealingly engage the first annular sealing surface; and

a fourth annular sealing surface which is formed concentrically in the stem bore and is configured to sealingly engage the second annular sealing surface;

wherein 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;

wherein in a second position of the valve stem, at least one of the first and second annular sealing surfaces does not sealingly engage its respective third or fourth annular sealing surface;

wherein the first and second seals together operate to seal the stem bore from fluid pressure in the gate cavity;

wherein the first position of the valve stem corresponds to one of the open position or the closed position of the gate; and

wherein the bonnet seal assembly further comprises first and second bi-directional seals which are mounted on the packing nut, the first bi-directional seal being sealingly engaged between the valve stem and the packing nut and the second bi-directional seal being sealingly engaged between the packing nut and the stem bore.

2. A gate valve comprising:

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, the bonnet comprising 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, the valve stem comprising a first end and an opposite second end which extends into the gate cavity;

a gate which is connected to the second end of the valve stem, the gate being 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 comprising:

a generally cylindrical packing nut which is positioned in the stem bore around the valve stem, the packing nut comprising 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 is configured to sealingly engage the first annular sealing surface; and

a fourth annular sealing surface which is formed concentrically in the stem bore and is configured to sealingly engage the second annular sealing surface;

wherein 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;

wherein in a second position of the valve stem, at least one of the first and second annular sealing surfaces does not sealingly engage its respective third or fourth annular sealing surface;

wherein the first and second seals together operate to seal the stem bore from fluid pressure in the gate cavity;

wherein the first position of the valve stem corresponds to one of the open position or the closed position of the gate; and

wherein the gate valve further comprises:

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.

3. A gate valve comprising:

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, the bonnet comprising 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, the valve stem comprising a first end and an opposite second end which extends into the gate cavity;

a gate which is connected to the second end of the valve stem, the gate being 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 comprising:

a generally cylindrical packing nut which is positioned in the stem bore around the valve stem, the packing nut comprising 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 is configured to sealingly engage the first annular sealing surface; and

a fourth annular sealing surface which is formed concentrically in the stem bore and is configured to sealingly engage the second annular sealing surface;

wherein 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;

wherein in a second position of the valve stem, at least one of the first and second annular sealing surfaces does not sealingly engage its respective third or fourth annular sealing surface;

wherein the first and second seals together operate to seal the stem bore from fluid pressure in the gate cavity;

wherein the first position of the valve stem corresponds to one of the open position or the closed position of the gate; and

wherein the bonnet seal assembly further comprises 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, the unidirectional seal being configured to seal against pressure in a portion of the stem bore located axially outwardly of the unidirectional seal.

4. A gate valve comprising:

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, the bonnet comprising 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, the valve stem comprising a first end and an opposite second end which extends into the gate cavity;

a gate which is connected to the second end of the valve stem, the gate being 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 comprising:

a generally cylindrical packing nut which is positioned in the stem bore around the valve stem, the packing nut comprising 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 is configured to sealingly engage the first annular sealing surface; and

a fourth annular sealing surface which is formed concentrically in the stem bore and is configured to sealingly engage the second annular sealing surface;

wherein 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;

wherein in a second position of the valve stem, at least one of the first and second annular sealing surfaces does not sealingly engage its respective third or fourth annular sealing surface;

wherein the first and second seals together operate to seal the stem bore from fluid pressure in the gate cavity;

wherein the first position of the valve stem corresponds to one of the open position or the closed position of the gate; and

wherein the packing nut is axially movably retained in the stem bore.

5. The gate valve of claim 4 , wherein the third annular sealing surface is 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.

6. The gate valve of claim 4 , wherein the bonnet seal assembly further comprises:

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;

wherein 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; and

wherein the second position of the valve stem corresponds to the other of the open position or the closed position of the gate.

7. The gate valve of any of claims 4 - 6 , wherein the bonnet seal assembly further comprises:

a stem packing which is positioned between the valve stem and the stem bore axially inwardly of the fourth annular sealing surface, the stem packing providing a pressure containing barrier between the gate cavity and the environment;

wherein 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

wherein 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.

8. The gate valve of claim 4 , wherein the stem bore comprises an enlarged diameter bore portion within which the packing nut is positioned, and wherein the fourth annular sealing surface is located at an axially inner end of the enlarged diameter bore portion.

9. The gate valve of claim 8 , wherein the first annular sealing surface is formed proximate an axially outer end of the packing nut and the second annular sealing surface is formed proximate an axially inner end of the packing nut.

10. The gate valve of claim 4 , wherein the packing nut is retained in the stem bore by a retainer nut which is secured to the bonnet axially outwardly of the packing nut.

11. The gate valve of claim 10 , further comprising a spring member which is positioned between the retainer nut and the packing nut and is configured to bias the packing nut axially inwardly.

12. A gate valve comprising:

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, the bonnet comprising 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, the valve stem comprising a first end and an opposite second end which extends into the gate cavity;

a gate which is connected to the second end of the valve stem, the gate being 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 comprising:

a generally cylindrical packing nut which is positioned in the stem bore around the valve stem, the packing nut comprising 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;

wherein 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;

wherein the first and second seals together operate to seal the stem bore from fluid pressure in the gate cavity;

wherein the first position of the valve stem corresponds to one of the open position or the closed position of the gate; and

wherein the third annular sealing surface is 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.

13. The gate valve of claim 12 , wherein the bonnet seal assembly further comprises:

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;

wherein 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; and

wherein the second position of the valve stem corresponds to the other of the open position or the closed position of the gate.

14. The gate valve of any of claims 12 , wherein the bonnet seal assembly further comprises:

a stem packing which is positioned between the valve stem and the stem bore axially inwardly of the fourth annular sealing surface, the stem packing providing a pressure containing barrier between the gate cavity and the environment;

wherein 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

wherein 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.

15. The gate valve of claim 12 , wherein the bonnet seal assembly further comprises first and second bi-directional seals which are mounted on the packing nut, the first bi-directional seal being sealingly engaged between the valve stem and the packing nut and the second bi-directional seal being sealingly engaged between the packing nut and the stem bore.

16. The gate valve of claim 12 , further comprising:

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.

17. The gate valve of claim 12 , wherein the bonnet seal assembly further comprises 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, the unidirectional seal being configured to seal against pressure in a portion of the stem bore located axially outwardly of the unidirectional seal.

18. The gate valve of claim 12 , wherein the stem bore comprises an enlarged diameter bore portion within which the packing nut is positioned, and wherein the fourth annular sealing surface is located at an axially inner end of the enlarged diameter bore portion.

19. The gate valve of claim 18 , wherein the first annular sealing surface is formed proximate an axially outer end of the packing nut and the second annular sealing surface is formed proximate an axially inner end of the packing nut.

20. The gate valve of claim 12 , wherein the packing nut is axially movably retained in the stem bore.

21. The gate valve of claim 20 , wherein the packing nut is retained in the stem bore by a retainer nut which is secured to the bonnet axially outwardly of the packing nut.

22. The gate valve of claim 21 , further comprising a spring member which is positioned between the retainer nut and the packing nut and is configured to bias the packing nut axially inwardly.