Background of the Invention

This invention relates generally to gate valves and more parti¬ cularly to an improved valve seat structure for expanding gate valves. Heretofore, problems have been experienced with expanding gate valve structures in maintaining the upstream and dov/nstream seat elements in parallel so that the expanding gate assembly can expand and create an effective seal with both of these seat elements. In the higher pressures (greater than 5,000 psi), it becomes extremely difficult to achieve an up¬ stream seal due to the large amount of operating torque required to expand the gate assembly into the upstream seat element. Earlier valve seat structures utilize a plastic insert extending from the front face of the seat element a specified distance so that the plastic insert conforms to the flatness and parallelism of the gate assembly prior to its expansion into metal-to-metal contact against the seat element. However, these plastic inserts have insufficient strength to adequately operate at pressures greater than 5, 000 psi. Other earlier structures utilize floating seat elements with front and rear seals which create a pressure energized upstream seal. How¬ ever, these structures cause the gate assembly to back wedge. In other words, once the gate assembly has collapsed and the gate is in motion, the valve seat structure continues to exert a load or pressure on the segment.

When the load overcomes the frictϊonal resistance associated with moving the segment relative to the gate, the segment will wedge up the gate causing the gate assembly to expand prematurely. This is, of course, very unde¬ sirable. In light of these problems, it would be highly desirable to provide an improved valve seat structure that compensates for out-of-paral- lelism and misalignment between the gate assembly and the upstream valve

seαt when the gat assembly is in the expanded condition. The valve seat structure of this invention performs this function without tending to cause back wedging of the gate assembly. Summary of the Invention It is an object of the invention to provide an improved valve seat structure that provides an adequate seal between the gate assembly and the upstream valγe seat at the time of expansion of the gate assembly into contact with the seat element without causing back wedging of the gate assembly. The invention is an improved valve seat structure for use in an expanding gate valve. The valve seat is positioned within an annular re¬ cess that is about a flow passage that communicates with the γalve chamber. The valve seat structure includes an annular seat element mounted in the annular recess having a front seat face adjacent the gate assembly. The front seat face has an annular groove which defines a pair of generally parallel inner and outer groove sides connected by a bottom. The bottom has a flat bottom and a frusto-conical portion with the flat bottom portion nearest to the flow passage and portion extending generally perpendicular to the inner and outer groove sides. The frusto-conical bottom portion which forms at feast approximately twenty-five percent (25%) of the width of the bottom is inclined facing the opening of the groove at an angle of between approximately thirty degrees (30°) and approximately sixty degrees (60o) with respect to the flat bottom portion to form a wedging surface.

An annular face seal is movably or loosely received within the annular groove for unrestrained movement therein. The annular face seal has a front seal face extending beyond the front seat face of the seat member outwardly of the groove, and a rear seal face having a frusto-conical rear portion that Ts in substantially flush contact and in conformity with the frusto-conical bottom portion of the groove. When the gate assembly is ex- panded, fluid originating from the flow passage is located between the inner seal side and inner groove side and this fluid wedgϊngly urges the annular face seal towards the gate assembly until its front seal face is pressed tightly against the gate assembly and the frusto-conical rear portion is wedged tightly against the frusto-conical bottom portion of the groove whereby a tight sealing relationship between the gate assembly and the valve seat is formed.

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When the gate assembly is collapsed, the annular face seal follows the inward movement of the gate assembly thereby allowing fluid to flow past the frusto-conical rear and bottom portions of the face seal and groove, respectively, to equalize the pressure on both sides of the face seal . Once the pressure is equalized, the face seal moves into a spaced or wiping relationship with the gate assembly. Brief Description of the Drawings

Fig. 1 is a sectional view of a balanced stem gate valve structur a portion shown in elevation, in which is positioned a specific embodiment of the improved valve seat structure;

Fig. 2 is an enlarged fragmentary sectional view of the central portion of Fig. 1 with the portions of the upstream and downstream valve seat structures nearest the handwheel shown in an enlarged sectional view with the, gate assembly In a fully open position and under pressure from the flow passage;

Fig. 3 Is an enlarged fragmentary sectional view of the central portion of Fig. 1 with the portions of the upstream and downstream valve seat structures nearest the handwheel shown in an enlarged sectional view with the gate assembly in a fully closed position and under pressure from the flow passage;

Fig. 4 is an enlarged fragmentary sectional view of the central portion of Fig. 1 with the portions of the upstream and downstream valve seat structures nearest the handwheel shown in an enlarged sectional view with the gate assembly moving from the closed position towards the fully open position and having just -reached a col lapsed position with the annular face seal having followed the collapse of the gate assembly towards the center of the valve chamber

Fig. 5 Is an enlarged fragmentary sectional view of the upstream valve seat structure remote from the handwheel of Fig. 1 with the gate assembly in a collapsed position;

Fig. 6 is an enlarged fragmentary sectional view of the upstream valve seat structure remote from the handwheel of Fig. 1 wherein the gate assembly is fully expanded and under pressure from the flow passage, and a seal is created between the valve seat structure and the gate assembly;

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Fig. 7 is an enlarged fragmentary view of the upstream valve seat structure of Fig. 1 remote from the handwheel wherein the annular face seal and annular groove are modified to Include a travel limiting assembly, and with the gate assembly in the collapsed position; and Fig. 8 is an enlarged fragmentary sectional view of the up¬ stream valve seat structure of Fig. 1 remote from the handwheel wherein the upstream valve seat structure is modified as in Fig. 7, and with the gate assembly In a fully expanded position and under pressure from the flow passage. Detailed Description of a Specific Embodiment

Figs. 1-6 illustrate a gate valve structure generally designated as 20. Gate valve structure 20 includes a valve body 21 In which Is a valve chamber 22. Valve chamber 22 places the inlet and outlet flow pas¬ sages 24 and 26 in fluid communication. A pair of flanges 28 are located at the ends of valve body 21 and are utilized to connect the gate valve structure to a flowline in a conventional manner well known to one skilled In the art. A bonnet 30 is bolted to the top of the valve body 21 , and a bearing housing 31 is secured to bonnet 30.

An expanding gate valve assembly or gate assembly is generally designated as 32 and is positioned within valve chamber 22 for reciprocal movement between open and closed positions therein generally transverse of the direction of fluid flow through inlet and outlet flow passages 24 and 26. The gate assembly 32 includes a gate 40 located adjacent the downstream or outlet flow passage 26 and a segment 50 located adjacent the upstream or inlet flow passage 24. As is conventional, the gate 40 and segment 50 are each provided with ports therethrough so that when the gate valve is fully open as appears in Fig. 1 , the ports are coaxially aligned with the flow passages 24 and 26. An operating stem 34 has the upper end (not illustra¬ ted) thereof connected to a handwheel 37, and the lower end 38 thereof connected to the gate 40. A valve stem 42 is connected at its upper end to the bottom end of gate 40 and depends downwardly therefrom. The lowe end of valve stem 42 is received in the lower portion of the valve body 21 typically In a sleeve (not shown) as is conventional . A more detailed des¬ cription of a suitable mounting of operating stem 34 and balancing stem 42 with valve body 21 is provided in United States Patent No. 3,923,285 issued on December 2, 1975, to Diehl et al .

Gαte 40 and segment 50 have complementary concave 52 and convex 54 faces, respectively, each of which have wedging surfaces thereon A spring 56 is anchored at the opposite ends thereof to gate 40 by a pair, of retaining lugs 58, and extends over and engages a flexing lug 60 that extends from segment 50. It should be understood that during travel of the gate assembly 32 between its open and closed positions as effected by turn¬ ing of the handwheel 37 and driving longitudinal movement of the operating stem 34, spring 56 maintains gate assembly 32 in its collapsed position. As gate assembly 32 reaches either its open or closed. position, segment 50 encounters valve body 21 and is rendered immovable. Gate 40 then moves relative to segment 50 and rides the wedging surface of convex face 54 so that gate 40 and segment 50 laterally expand apart from each other. When gate assembly 32 Is displaced from its fully expanded position, spring 56 facilitates the immediate collapse of gate 40 and segment 50 into their col lapsed position.

As will become apparent from the following discussion, the valve seat structure of this invention provides improved operating characteristics heretofore unavailable in expanding gate valves, and particularly in expand¬ ing gate valves operating at pressures greater than 5, 000 psi. The following description of the valve seat structure wil l not differentiate between the

^• upstream and downstream members. However, the description of the operatio of the invention will differentiate between the upstream (unprimed and down¬ stream (p r I m ed ) m em be rs .

An annular recess 62 is formed in the valve body 21 about the inlet and outlet flow passages 24 and 26 adjacent valve chamber 22. An annular metallic seat element 64 is fitted within annular recess 62. An¬ nular metal lic seat element 64 has a front seat face 66 in which is formed an annular groove 70 which Is defined by generally parallel inner and outer groove sides 72 and 74 that are joined by a bottom 76. Annular groove 70 has a width "W" measured between the inner and outer groove sides, and a depth "D" measured between front seat face 66 and bottom 76. The depth "D" of groove 70 is preferably around one and one-half (1-1/2) times greater than width "W". Depth "D" between approximately one and one- fourth (1- 1/4) and one and three-fourths (1/3/4) times greater than width "W" would function effectively.

Bottom 76 includes α flat bottom portion 78 that Is generally perpendicular to and adjacent to inner groove side 72 which is the side nearest the flow passage, and a frusto-conical bottom portion 80 that is formed adjacent to outer groove side 74. Frusto-conical bottom portion 80 comprises between approximately twenty-five percent (25%) and approximate¬ ly seventy percent (70%) of the width "W ^M of annular groove 70 (this dimen¬ sion is shown as "Wl "), and between approximately twenty percent (20%) and approximately fifty percent (50%) of the depth "D" of annular groove 70 along outer groove side 74 (this dimension is shown as "Dl "). The dimension of flat bottom portion 78 is represented ^* by the designation "W2". The dimension of outer groove side 74 is represented by the designation "D2". Frusto-conical bottom portion 80 is disposed from flat bottom portion 78 at an angle "A" which is within a range of between approximately thirty degrees (30°) and approximately sixty degrees (60°). An annular face seal 82 is positioned or loosely received in an¬ nular groove 70 for relatively unrestrained movement therein. Annular face seal 82 Includes opposite front and rear seal faces 84 and 86 joined together by Inner and outer seal sides 88 and 90. Annular face seal 82 Is of a thickness "T" as measured between the inner and outer seal sides, and Is of a length ^M L" as measured between the front and rear seal faces. The length "L" of face seal 82 Is between approximately 1 .4 and 1 .6 times the thickness "T" thereof. Rear seal face 86 includes a flat rear portion 92 that is gen¬ erally perpendicular and adjacent to inner seal side 88, and a frusto-conical rear portion 94 that is formed adjacent to outer seal side 90. Frusto-conical rear portion 94 comprises between approximately twenty-five percent (25%) and approximately seventy percent (70%) of the thickness of annular face seal 82 (this dimension is shown as "Tl "), and between approximately twenty percent (20%) and approximately fifty percent (50%) of the length of an¬ nular face seal 82 along its outer seal side 90 (this dimension Is shown as "LI "). The dimension of flat rear portion 92 of rear seal face 86 is re¬ presented by the designation "T2". The dimension of outer seal side 90 is represented by the designation "L2 ^W . Frusto-conical rear portion 94 is dis¬ posed from flat rear portion 92 at an angle "B" which Is within a range of between approximately thirty degrees (30°) and approximately sixty degrees (60°). For expanding gate valves of standard commercial sizes, front seal

fαce 84, when the gate is in the collapsed condition, extends past front seat face 66 a distance "E" which is within a range of between approxi¬ mately .002 inches (.0051 cm) and approximately .015 inches (.0381 cm). The dimensions of a specific embodiment of the valve seat structure in a 2 and 9/16th inch (6.51 cm) 20, 000 psi expanding gate valve are set forth below; however, it is intended that the recitation of a particular size of valve or the dimensions are not limiting as to the scope of applicants' invention:

W = . 130 inches (.331 cm) Wl = .06 inches (. 152 cm)

W2 = .07 inches (. 178 cm) D = .181 inches (.46 cm) . Dl = .06 inches (. 152 cm) ^" D2 = . 121 inches (.308 cm) T = . 120 Inches (.304 cm)

Tl = .055 Inches (. 14 cm) T2 = .065 inches (. 165 cm) L = . 190 inches (.483 cm) LI = .076 inches (. 1 3 cm) L2 = . 114 inches (.29 cm)

A = 45° = B

E = .006 inches (.0152 cm)

With the face seal 82 sitting loosely in the annular groove 70 with its frusto-conical surface engaging the frusto-conical bottom surface of the groove, the clearance between groove side 74 and seal side 90 is in the range of .001 inches to .015 inches. Clearance between seal side 88 and groove side 72 is .021 inches, and preferably in the range of "E" + .015 inches. It is the same clearance as between the rear seal face 92 and groove bottom 78. The face seal 82 may be of a resilient plastic material, such as

Teflon, but for operating at high temperatures greater than 500° F. (260°C) or at high pressures greater than 10,000 psi, a metal lic face seal is required. In such instances, an aluminum bronze alloy' or a soft stainless steel, such as 316 stainless steel, would be a suitable material.

Fig. 5 i llustrates the valve seat structure of the invention when gate assembly 32 is In its collapsed position for longitudinal travel within valve chamber 22. The fluid pressure on inner seal side 88 and outer seal side 90 is equal so that both the upstream and downstream annular face seals 5 (only the upstream face seal is illustrated in Fig. 5) are in a wiping relation¬ ship with gate assembly 32. When in this wiping relationship with gate assembly 32, front seal face 84 Is spaced apart a small distance from the gate assembly so as to provide a beneficial wiping of the adjacent surface of the collapsed gate assembly 32 which reduces the amount of contaminants

10 that enter valve chamber 22. When in this wiping relation, annular face seal 82 does not impede or bind the movement of gate assembly 32 within valve chamber 22 since its inward movement or float is limited by frusto- conical rear portion 94 reaching its end of travel on frusto-conical bottom portion 80. In this wiping relation, while the spacing between front face

15 seal 84 and gate assembly 32 may vary with the size of the valve, for ex¬ panding gate valves of standard commercial sizes it is generally approximate¬ ly .020 inches (.051 cm).

Fig. 3 illustrates the gate assembly in Its closed position. As gate assembly 32 reaches its closed position, it expands against both upstream

20 and downstream annular face seals 82 and 82* so that they are axially com¬ pressed to form a fluid-tight seal between themselves and gate assembly 32 and their respective annular grooves 70 and 70' . With respect to upstream annular face seal 82, fluid from inlet flow passage 24 then travels along the upstream side of segment 50 and into upstream annular groove 70, and

25 Is contained within a space between inner groove side 72 and inner seal side 88. The fluid does not leak past either the front or rear seal faces of annular, face seal 82 due to the above described seal created between It and gate assembly 32 and upstream annular groove 70. As the fluid pressure builds within the space between the outer groove and seal sides, upstream

30 annular face seal element 82 is forced to travel on its frusto-conical rear portion 94 up frusto-conical bottom portion 80. As upstream annular face seal 82 travels up frusto-conical bottom portion 80, it moves Inwardly towards gate assembly 32 while gate assembly 32 simultaneously expands outwardly towards it. Fluid pressure built up In the space defined between flat bottom

35 portion 78 and flat rear portion 92 also forces upstream annular face seal 82

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to travel inwardly toward valve chamber 22 and gate assembly 32. Thus, an effective seal which surrounds the flow passage is created between front seal face 84 and gate assembly 32, and between frusto-conical rear portion 94 and annular groove 70. Because fluid from the flowline actually forces the upstream annular face seal to wedge towards the gate assembly, the ef¬ fectiveness of the seal created by the annular face seal increases with in¬ creasing flow passage fluid pressure. The inward travel of the annular face seal towards the gate assembly reduces the distance the gate assembly must move against the direction of fluid flow in the flow passage. It can thus be seen that the ability of annular face seal 82 to move inwardly in response to fluid pressure in the flow passage facilitates the formation of an effective seal on the upstream side of gate assembly 32 without the need for exerting operating torques on the gate assembly of such degrees as has been required in the past. With respect to the downstream annular face seal 82' , when the gate assembly is placed in its closed position, the downstream annular face seal remains slightly axially compressed between frusto-conical bottom portion 80' of downstream annular groove 70' due to the expansion of gate assembly 32. However, because fluid does not flow into downstream annular recess 70', downstream annular face seal 82' does not wedge inwardly towards valve chamber 22.

Fig. 2 illustrates the gate assembly in its open position In which it is also fully expanded and the ports through gate 40 and segment 50 are fully aligned. As gate assembly 32 reaches its open position, both the up- stream and downstream annular face seals 82 and 82' are axially compressed to initially seal against gate assembly 32 and their respective annular grooves 70 and 70' in a manner similar to that when the gate assembly reaches Its closed position. However, because fluid from the flow passage has entered the valve chamber during the movement of the gate assembly the fluid pres- sure on both sides of the upstream and downstream annular face seals is equal and the upstream and downstream annular face seals are not axially compressed any further by wedging Inwardly towards valve chamber 22.

Referring to Fig. 4, when gate assembly 32 is in longitudinal movement towards the fully open position and just collapses from its closed position, front seal face 84 of upstream annular face seal 82 continues to contact gate assembly 32 and follows gate assembly 32 Inwardly towards valve

chαmber- 22. As α result of this, frusto-conical rear portion 94 of upstream annular face seal 82 moves away from frusto-conical bottom portion 80 of upstream annular groove 70, and fluid contained between the inner sides and flat portions of upstream annular groove 70 and upsteam annular face seal 82 flows past these frusto-conical rear and bottom portions 94 and 80 to the outer sides of upstream annular groove 70 and upstream annular face seal 82 thereby equalizing the fluid pressure on both sides of upstream annular face seal 82. Once the fluid pressure on both sides of upstream annular face seal 82 Is equalized. It moves back into its wiping relationship with the gate assembly as illustrated in Fig. 5.

Figs. 7 and 8 illustrate a modified embodiment of the specific embodiment illustrated In Figs. 1-6. The embodiment illustrated in Figs. 7 and 8 is dimensJonafty and operativejy similar to that Illustrated in Figs. 1-6 with the exception of the addition of a travel limitation assembly generally designated ai 100. It is particularly suited for large bore valves or valves utilized in high yelocity flow conditions where the face seal might other¬ wise be severely flexed. In this embodiment an annular groove recess 102 -is contained within annular groove 70A in seat element 64A and is in an opposed facing relationship with an annular seal recess 104 formed in annula face seal 82A. Annular groove recess 102 has forward and rearward sides

108 and 1 10, and annular seal recess 104 has forward and rearward sides 112 and 1 14. An annular ring 106 or stop member is fitted within annular groov recess 102 and extends into annular seal recess 104. The annular ring is made of a hard metal, such as stainless steel or Inconel. The annular groove 70A and seal recesses 102, 104 are dimension ed relative to annular ring 106 such that the movement of annular face seal 82A inwardly toward the gate assembly and valve chamber 22A is limited by interference between annular ring 106 and rearward surface 1 14 of annula seal recess 104 and forward surface 108 of annular groove recess 102. This Inward travel is limited such that when the fluid pressure on both sides of face seal 82A Is equalized, the distance the annular face seal moves toward the valve chamber is limited to that distance wherein the annular face seal is in Its wiping relationship with the gate assembly. However, when the gate assembly first collapses, the face seal is permitted to travel a sufficient distance to allow the fluid pressure on both sides thereof to become equalize

ln no case does the face seal extend such a distance to cause a back wedg ing of the gate assembly.

The valve seat structure of the invention is also useful in a double block and bleed gate valve application. In this type of application pressurized fluid is applied to both sides of the gate assembly. Consequentl when the gate assembly is closed, the annular face seals 82 and 82' on bot sides of the gate assembly act like the upstream face seal described above to form pressure energized seals on both sides of the gate assembly.

It will therefore be seen that a new and improved valve seat structure for expanding type gate valves is disclosed herein. In particular, it is very effective for achieving an upstream seal in the higher pressures (greater than 5, 000 psi) without requiring a large amount of operating torqu to expand the gate assembly into the upstream seat element. It is also ada able to operation at these higher pressures in high temperature environments greater than 500°F. (260°C).

The foregoing description of the Invention has been presented for purposes of illustration and explanation and is not intended to limit the in¬ vention to the precise form disclosed as changes in details of the illustrated construction may be made by those skilled In the art, within the scope of the appended claims, without departing from the spirit of the invention. For example, the flat bottom portion 78 of the annular groove 70 could be mad very small or eliminated and the flat rear portion 92 of the annular face sea 82 made correspondingly small or reduced to the form of a rounded edge. It is intended that the scope of the invention be defined by the claims append ed hereto.