Floating plug gate valve

A gate valve has a gate that moves in a gate cavity between a lower closed position and an upper open position. A seal member in the gate seals against a downstream seat ring when the gate is in the closed position. The seal member is moveable in upward and downward directions as well as upstream and downstream directions relative to the gate. The seal member is in an upper and downstream position relative to the gate while the gate is in the closed position. A cam member is carried by the gate for movement in unison and is in engagement with the seal member. The cam member moves the seal member to an upstream and downward position in response to initial movement of the gate from the closed position toward the open position.

FIELD OF THE INVENTION

This invention relates in general to gate valves, and in particular to a gate valve having a feature for reducing wear on the sealing surfaces of the gate.

BACKGROUND OF THE INVENTION

A gate valve has a body with a flow passage extending through it. A gate cavity intersects the flow passage, and seat rings are located at the upstream and downstream points of intersection. An actuator, which may be mechanical, hydraulic or electrical, moves a gate within the cavity between open and closed positions. In the closed position, a seal surface on the gate contacts the downstream seat ring. The upstream pressure exerts a force pushing the seal surface into tight sealing engagement. The gate has an aperture through it next to the seal surface. When in the open position, the aperture registers with the flow passage.

When the operator begins to open the gate valve, the seal surface of the gate slides across the seat ring as the gate moves to the open position. The upstream pressure force continues to act on the gate until the aperture reaches the seat rings. If the upstream pressure force is high, a considerable friction force results even if the seal surface and the seat rings are smooth surfaces and lubricants are employed. This frictional force can damage the seal surfaces of the seat ring and gate.

SUMMARY

The gate valve has features to cause the seal surface of the gate to move away from the seat ring when the gate begins to open, rather than drag across the seat ring. The gate valve has a seal member mounted to the gate that seals against the downstream seat ring when the gate is in the closed position. A cam member is carried by the gate in cooperative engagement with the seal member. The cam member moves the seal member in an upstream direction in response to beginning movement of the gate from the closed position toward the open position. This movement pulls the seal member away from the seat ring upon initial movement of the gate.

In the preferred embodiment, the seal member moves in upstream and downstream directions relative to the gate. Also, the seal member is movable in closing and opening directions relative to the gate. The cam member is movable in unison with the gate and has a cam surface that engages a portion of the seal member so as to push the seal member in a direction that is between the closing direction and the upstream direction.

In the example shown, the seal member is a plug located within a plug hole extending through the gate from an upstream side to a downstream side, the plug having a downstream end that contacts and seals against the downstream seat ring. In the same example, the cam member is a key mounted to the gate for movement therewith, the key extending through a key hole in the plug that is transverse to the plug hole. The key hole is configured to allow the plug to move relative to the key in a downward and upstream direction and an upward and downstream direction. The key hole is configured to prevent the plug from moving relative to the key in an upward and upstream direction and in a downward and downstream direction.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, valve11has a body13with a gate cavity15located therein. Flow line passages17,19, which extend through body13, are coaxial with each other about an axis20and intersect gate cavity15. A gate21is carried within cavity15for movement in a plane perpendicular to axis20of flow line passages17,19. Gate21is generally rectangular, having upstream and downstream flat sides.

In this embodiment, gate21is moved by a rising stem23, wherein stem23does not rotate, rather it moves linearly outward from body13along stem axis24as gate21is being lifted. Alternately, gate21could have a threaded nut on its upper end and be moved by a rotating non-rising stem (not shown). Stem23has a T-member25on its lower end that fits within a receptacle at the upper end of gate21in this embodiment. Stem23has threads27on its upper end that engage a rotatable sleeve nut29. Sleeve nut29is carried within a bonnet31mounted to the upper end of body13. A hand wheel33is employed to rotate sleeve nut29relative to threads27to cause stem23to move linearly along its axis24. Alternately, a hydraulic or electric actuator could be utilized to cause axial movement of stem23. A stem seal35located in bonnet31seals around stem23and seals pressure within gate cavity15.

A seat ring37,38is mounted at the intersection of each flow passage17,19, respectively, with gate cavity15. Seat rings37,38have holes39therethrough and seal surfaces on their inward directed faces for sealing against the sides of gate21. The distance between the seal surfaces of seat rings37,38is slightly greater than the thickness of gate21. Seat rings37,38may be biased by springs toward each other.

In this embodiment, gate21is a single slab type, but it could be a split type, which would have two separate halves. Gate21has a flow passage or aperture41that registers with flow passages17,19and holes39in seat rings37,38when the gate is in a fully open position. The inner diameter of gate flow passage41is typically the same as holes39in seat rings37,38and flow passages17,19.

Gate21has a seal member, which in this example, comprises a plug43located in a transverse bore45that is parallel to and located above gate flow passage41. The terms “upward”, “downward”, “above”, and “below” are used only for convenience because gate valve11may be installed in various positions, other than with stem25pointing upward. Seal plug43is preferably a cylindrical member with an outer diameter that is larger than the inner diameter of gate valve flow passage41and also larger than the inner diameter of holes39in seat rings37,38. Seal plug43could have shapes other than cylindrical. Seal plug43has flat seal ends47,49located in parallel planes. The distance between ends47,49may be slightly less than the width between the upstream and downstream sides of gate21. Also, the distance between ends47,49is less than the distance between seat rings37,38, resulting in a slight gap50between upstream plug end49and seat ring38when gate21is closed and under pressure from flow passage19, as shown inFIG. 3. When not under pressure, seal plug43can slide freely back and forth in bore45along its axis relative to gate21.

Seal plug43is also capable of moving in upward and downward directions relative to gate21. If seal plug43is cylindrical, as shown, the outer diameter of seal plug43is made slightly less than the inner diameter of plug bore45, allowing slight upward and downward movement of seal plug43relative to gate21in a direction perpendicular to axis24of stem23. Gap46between the outer diameter of seal plug43and the inner diameter of plug bore45is shown on the upper side of seal plug43inFIG. 4. When seal plug43moves upward slightly relative to gate21, gap46exists on the lower side of seal plug43, as shown inFIG. 3, rather than the upper side.

A cam member51is employed to cause seal plug end47to pull away from downstream seat ring37when gate21begins to move from its closed position. In this embodiment, cam member51comprises a key51that extends through mating gate key holes53in gate valve21. In this example, key hole53passes through the intersection of flowline axis20and stem axis24. Key51also extends through a plug key hole or slot55in seal plug43, as shown also inFIG. 2. Key51has a length greater than the outer diameter of seal plug43and approximately equal to the width of gate21measured from one side edge to the other side edge. Key51has an axis that is perpendicular to the axis of seal plug43as well as to the stem axis24. Key51moves in unison with gate21, and seal plug43moves slightly relative to key51and gate21when gate21begins to move from its closed position.

In this embodiment, key51has a generally diamond-shaped configuration, although other configurations are feasible. Referring toFIG. 5, key51has flat flanks or sides51a,51b,51cand51d. Sides51aand51care parallel to each other, and sides51band51dare parallel to each other. Side51afaces generally upward and upstream; side51cfaces generally downward and downstream. Side51bfaces generally upward and downstream; and side51dfaces generally downward and upstream. In this example, the width of key51is less than its height as measured in the cross-sectional view ofFIG. 5. The included angles between sides51aand51dand between sides51band51care the same and obtuse. Similarly, the included angles between sides51aand51band between sides51cand51dare the same and acute. Gate valve key hole53has mating sides53a,53b,53cand53dthat tightly engage key sides51a,51b,51cand51d. Preferably, key51is substantially immovable relative to gate21because of the tight engagement with gate valve key hole53.

Referring toFIG. 4, plug key hole55differs in dimensions from key51so that key51can move slightly relative to seal plug43. In this example, plug key hole55has a diamond-shaped configuration with sides55a,55b,55cand55d. Preferably parallel plug key hole sides55aand55care substantially the same distance apart as key parallel sides51aand51c. However, the distance between plug key hole sides55band55dis greater than the distance between the key sides55band55d. This results in a gap59, which could be either on key side55b, key side55dor partially on both. As shown inFIG. 2, key51has ends57that are flush with side edges of gate21.

FIG. 4illustrates an idealized neutral position when gate21is in a closed position but no flow line pressure exists, and in this position, part of gap59is shown between sides51dand55dand part of gap59is shown between sides55band51b. As will be explained subsequently, while in the closed position with pressure in flow passage19, as shown inFIG. 3, gap59is located only between downstream sides51band55b, and upstream sides51dand55dare touching each other. When moving from the closed position inFIG. 3to an open position, as illustrated inFIG. 6, key gap59will exist only on the upstream side, between sides51dand55d, and downstream sides51band55bwill be touching each other. In each of these instances, when only a single gap59exists, it will be equal in width to the two gaps59shown inFIG. 4.

In operation,FIG. 4illustrates a possible position for seal plug43while gate21is in the fully closed position without any pressure in passages17,19. A slight plug end gap50may exist between seal plug end47and seat ring37, A plug end gap50may also exist between seal plug end49and seat ring38. Plug end gaps50would not likely be identical, but they could be approximately the same. Plug diameter gap46would normally be located between the outer diameter on the upper side of seal plug43and plug bore45. Because of the weight of seal plug43, its outer diameter would typically be contacting plug bore45on the lower side. Typically key gaps59would exist both between downstream sides51band55bas well as upstream sides51dand55d, although key gaps59would not likely be exactly equal.

With flow line pressure applied to an upstream side, which is considered to be flow passage19in this example, a force Px (FIG. 4) parallel to axis20occurs. Force Px acts on plug upstream end49and tends push seal plug43downstream to the left. While the entire gate21might shift slightly to the left, plug43is able to move farther to the left than gate21because it is able to move relative to key51. As indicated by the vector arrow Pxy, the movement of plug43relative to gate21is upward and to the left or downstream. This upward and downstream movement will cause plug end gap50on the downstream end47to completely close up and plug end gap50on the upstream end49to increase. Also, plug diameter gap46will decrease on the upper end and increase on the lower end because of the upward component of the movement of plug43relative to gate21. The closed position with pressure in flow passage19is illustrated inFIG. 3. A tight seal is formed between the outer margin of downstream plug end47and its mating downstream seat ring37. Plug end gap50is now entirely on the upstream side between plug upstream end49and its upstream seat ring38. The force exerted by the pressure in flow passage19maintains plug43in the sealed position shown inFIG. 3.

In the prior art, when the operator wishes to move a gate from a closed position under high pressure to an open position, normally a high frictional force between the gate and the downstream seat ring would have to be overcome. In this gate valve, a high frictional force between the outer margin of seal plug end47and seat ring37does exist because of the sealing engagement and high pressure. However, as the operator causes gate21to begin moving upward, gate21will initially move upward a slight distance relative to seal plug43because of outer diameter gap46on the lower side and because of key gap59on the upper downstream side of key51. During the initial upward movement of gate21, gate21does not touch downstream seat ring37. As gate21begins to move upward, key51also begins to move upward in unison, as indicated by the arrow Ly inFIG. 4, which creates an immediate relative movement between key51and plug43as indicated by the arrow Lxy. The direction of the vector Lxy is both downward and in an upstream direction relative to key51. The close contact between upstream key side51aand key hole51bresults in plug43moving upward and upstream relative to downstream seat ring37. Gap59between upper sides51b,55bbegins to close and gap59begins to appear now between the lower upstream sides51dand55d. The movement of seal plug43upstream and upward slightly relative to gate21occurs as the same time gate21begins moving upward, thus immediately breaks the sealing contact between seal plug end47and seat ring37. Plug end gap50will then appear on the downstream side between seal plug end47and seat ring37, and plug end gap50on the upstream side between seal plug end49and seat ring38will decrease. This position is illustrated inFIG. 6.

As mentioned, because of the initial upstream component of the movement of seal plug43relative to seat ring37when gate21begins moving upward, the sealing engagement breaks quickly between the downstream seal plug end47and downstream seat ring37. With the sealing engagement breaking, plug end gap50immediately appears between downstream plug end47and seat ring37. Thus as gate21continues to move upward, seal plug end47does not drag across the seal surface of seat ring37.

The gate valve described herein has significant advantages. The plug and key arrangement causes the seal surface of the gate to immediately pull away from the downstream seat ring when the gate begins to open. This feature reduces damage to the seal surfaces that might otherwise occur in high pressure applications.

While the gate valve has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without detracting from its advantages.