Expanding gate valve having mechanically secured seats
BACKGROUND OF THE INVENTION 
     This invention relates generally to the field of valves and deals more specifically with positively retained valve seats which find particular utility in expanding type gate valves. 
     Expanding gate valves usually have fixed valve seats which are pressed in place in their seat pockets. Fixed seats of this type are not able to effectively compensate for lack of parallelism in the surfaces of the gate mechanism and seats, or for the other irregularities and imperfections that are inevitably present in the valve components. Moreover, pressed in seats are not positively held in place and tend to work their way out of the seat pockets, especially after the valve has been cycled repeatedly. Another drawback associated with the pressed in seat is the close tolerances that are required if the seat is to fit properly in place when the valve is assembled. A large percentage of seats fall outside of the acceptable tolerances and must be scrapped or reworked, thereby significantly increasing the cost of the valve. Pressed in seats are also difficult to replace in the field and to repair or recondition after prolonged use. 
     As an alternative to seats which are pressed in place, valve seats which are mounted for &#34;floating&#34; or limited floating movement toward and away from the gate have been proposed. This type of seat compensates for lack of parallelism and other irregularities in a generally satisfactory manner, although the added complexity of the valve body and seats caused problems with respect to economical manufacture and assembly of the valve. Furthermore, floating seats require a large cavity in the valve body in order to accommodate the various types of inserts that are used to limit the floating movement, and the size and weight of the valve are increased accordingly. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a valve having seats which are mechanically retained in place in an improved manner as compared to the fixed and floating type seats that have been proposed in the past. Although the valve seats disclosed herein are similar in a broad sense to those shown in U.S. Pat. No. 683,695 to Lundbom, they are improved in a number of respects, most notably in their ability to accommodate imperfect surfaces of the gate assembly. 
     It is an important object of the invention to provide an expanding gate valve in which the seats and seat pockets do not require close tolerances in order to function effectively. 
     Another object of the invention is to provide valve seats which may be quickly and easily installed and removed and which are positively held in place in their seat pockets. 
     Yet another object of the invention is to provide an expanding gate valve which is constructed in a manner permitting efficient high volume production without requiring significant scrapping or rework of the valve seats. 
     Still another object of the invention is to provide an expanding gate valve of the character described which may be manufactured economically without requiring difficult machining operations or complex machine tools. 
     These and other advantages of the invention are achieved by providing an expanding gate valve having seats which are mechanically held in place in their seat pockets and yet are provided with enough play to compensate for ordinary irregularities in the valve components. In accordance with the invention, each valve seat has a pair of diametrically opposed lugs projecting outwardly therefrom. Each seat pocket in the valve body has an undercut groove which is intersected at diametrically opposed locations by a cylindrical body cavity formed in the valve body. Such intersections provide access to the undercut grooves so that the lugs may be inserted therein and the valve seats may then be rotated to lock the lugs in place, thereby securing the valve seats in their pockets. Tapered surfaces on the lugs interact with the undercut grooves in camming fashion to lock the seats more firmly in place with progressive rotation of the seats. As a particularly important feature of the invention, the lugs form a pivot axis along a diameter of each valve seat so that the seats are free to pivot in order to effectively seal against the gate assembly despite lack of parallelism or other imperfections in the surfaces of the gate assembly or valve seats. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings which form a part of the specification and are to be read in conjunction therewith: 
     FIG. 1 is a sectional view of an expanding gate valve constructed in accordance with a preferred embodiment of the present invention, with the gate assembly in the open position; 
     FIG. 2 is a fragmentary sectional view on an enlarged scale taken generally along line 2--2 of FIG. 1 in the direction of the arrows; 
     FIG. 3 is an enlarged fragmentary view of one of the valve seats taken generally along line 3--3 of FIG. 2 in the direction of the arrows, but with the seat rotated to a position wherein it can be inserted into or removed from its seat pocket; 
     FIG. 4 is an enlarged fragmentary view of one of the valve seats taken generally along line 4--4 of FIG. 1 in the direction of the arrows, but with the seat rotated to a position wherein it may be inserted into or removed from its seat pocket; 
     FIG. 5 is an exploded perspective view showing the manner in which the seats are installed and a tool for installing and removing the seats, with portions of the valve body broken away for purposes of illustration; and 
     FIG. 6 is a top plan view of one of the valve seats taken generally along line 6--6 of FIG. 4 in the direction of the arrows and showing the seat inserted in the seat pocket prior to rotation of the seat to lock it in place, with the valve body shown in broken lines. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With initial reference to FIG. 1, numeral 10 generally designates an expanding gate valve constructed in accordance with the present invention. Valve 10 includes a valve body 12 presenting a flow passage 13 therethrough which includes an inlet passage 14 and an aligned outlet passage 16. Body 12 has flanges 18 and 20 on the respective inlet and outlet ends thereof, and each flange has a plurality of bolt holes 22 to facilitate connection of the valve with a fluid flowline (not shown). A cylindrical valve chamber or body cavity 24 is formed through body 12 at a location between the inlet and outlet flow passages 14 and 16. Body cavity 24 extends perpendicular to flow passage 13 and intersects therewith at a right angle in a manner that will be described in more detail. 
     Valve 10 includes an expanding gate assembly which is generally designated by reference numeral 26. Gate assembly 26 is mounted for reciprocal movement in body cavity 24 and may be constructed in a conventional manner. The gate assembly includes a gate 28 and a segment 30 which cooperate with one another in the open position of the valve to provide a port 32 aligned with the flow passage 13. Gate 28 and segment 30 have mating inclined surfaces 34 and 36 which interact with one another in camming fashion to expand the gate assembly in both its opened and closed positions, as will be explained in more detail. Gate 28 has an outwardly facing surface 38 which is a flat surface oriented parallel at all times to a flat outwardly facing surface 40 on segment 30. A pair of curved springs 42 engage pins 44 on opposite sides of gate 28 and segment 30 in a manner to continuously urge the gate and segment toward one another to bias the gate assembly toward a collapsed position. 
     A valve stem 46 extends upwardly from the top of gate 28 through a valve bonnet 48 which is mounted on top of body 12 by a series of bolts 50 and nuts 51. Packing 52 forms a fluid-tight seal between stem 46 and bonnet 48, while a seal ring 53 forms a fluid-tight seal between the valve body and bonnet. An internally threaded drive sleeve 54 engages stem 46 in threaded fashion and is supported for rotation in bonnet 48 by a pair of thrust bearings 56. Bearings 56 are mounted within a bearing housing 58 which is secured on bonnet 48. Drive sleeve 54 has an enlarged collar portion 60 located between bearings 56. A handwheel or the like (not shown) is connected with sleeve 54 in order to facilitate rotation of the sleeve to move stem 46 and gate 28 upwardly and downwardly between the open and closed positions of the valve. 
     A balancing stem 62 extends downwardly from the bottom end of gate 28. Stem 62 extends into a base 64 which is secured by bolts 66 and nuts 67 to the bottom of body 12 and is sealed thereto by a seal ring 68. Packing 70 provides a seal between base 64 and stem 62. Balancing stem 62 is reciprocal within a sleeve fitting 72 secured to the bottom of base 64 below packing 70. Although the valve shown herein is a high pressure valve and is equipped with balancing stem 62, it is to be understood that the present invention is useful in other types of valves. 
     Valve 10 has a pair of valve seats 74 which are constructed identically and which face inwardly toward one another on opposite sides of gate assembly 26. To receive seats 74, a pair of annular seat pockets 76 are formed about flow passage 13 at locations adjacent body cavity 24 on the upstream and downstream sides thereof. Each seat pocket 76 is provided with an undercut annular groove 78 located at the end of the seat pocket remote from gate assembly 26. Each undercut groove 78 is concentric with flow passage 13 and is located outwardly thereof. As shown in FIGS. 2 and 5, body cavity 24 is cylindrical and intersects with each undercut groove 78 at two diametrically opposed locations on the groove in order to form a pair of diametrically opposed openings 80 to each groove. At all other portions of each groove 78, a flat annular surface 82 of the groove faces away from gate assembly 26 and body cavity 24, as best shown in FIG. 6. The back surface of each groove 78 coincides with a flat annular back surface 84 of the corresponding seat pocket 76. Surface 84 is parallel to surface 82 and faces inwardly toward cavity 24. Openings 80 to each undercut groove 78 are arranged directly above one another along a line extending parallel to the longitudinal axis of body cavity 24. 
     Each valve seat 74 is an annular member having a hub portion presenting a cylindrical opening therethrough which is aligned with the flow passages 14 and 16 and with port 32 in the open position of gate assembly 26. Each seat 74 has on its inner portion an enlarged rim presenting a flat, annular, inwardly facing seating surface 86 for sealing contact with gate assembly 26 in the opened and closed positions thereof. As best shown in FIG. 3, surface 86 carries a seal ring 87 which may be formed of any suitable material capable of effectively sealing with the gate assembly, such as metal &#34;Teflon&#34; material or the like. Alternatively, seal ring 87 may be eliminated and surfaces 86 may seal directly against surfaces 38 and 40 of the gate assembly. The back surface of each valve seat 74 is a flat annular surface provided with a crush ring 88 or another type of seal which is capable of effectively sealing against back surface 84 of the seat pocket. 
     Each valve seat 74 is provided with a pair of outwardly projecting lugs 90 which are spaced well away from seating surface 86 on the outer end portion of the seat. Lugs 90 project radially outwardly from the valve seat at diametrically opposed locations thereon and are small enough to fit through openings 80 and into undercut groove 78. As best shown in FIG. 6, each lug 90 has a tapered surface 92 facing inwardly toward surface 82 of groove 78. Surface 92 is preferably oriented at an angle of between 1° and 10° relative to seating surface 86 in order to effectively interact with surface 82 in camming fashion, as will be explained more fully. The thickness of each lug 90 in the direction of the flow passage of the valve is slightly less than the depth of groove 78 at the minimum lug thickness, while the maximum lug thickness is slightly greater than the depth of groove 78 in the preferred form of the invention. Each lug 90 has a beveled surface 94 to facilitate entry of the lug into groove 78. 
     As shown in FIGS. 3 and 5, the rim portion of each valve seat 74 has a pair of diametrically opposed notches 96 formed in its periphery. Inwardly of seal ring 87, surface 86 of each valve seat is provided with a pair of diametrically opposed openings 98. A tool which is used to insert and remove seats 74 includes a bar 100 having a length to substantially span the seating surface 86 of each valve seat. Bar 100 has a pair of spaced apart pegs 102 projecting therefrom to fit closely into openings 98 when the tool is applied to the valve seat. Alternatively, pegs 102 may be arranged to fit in notches 96, thus eliminating the need for openings 98. A detachable handle 104 for the tool has a projection 106 which is square in cross section and which fits closely in a square cavity 108 formed centrally in bar 100. 
     With reference again to FIGS. 1 and 2 in particular, each valve seat 74 has a seat skirt 110 which is constructed to fit closely around the periphery of the seat at a location adjacent seating surface 86. Each skirt 110 has a pair of flanges 112 on opposite sides thereof to assist in guiding gate assembly 26 between its open and closed positions. A pair of pins 114 (FIG. 1) project outwardly from each seat skirt 110 and fit closely in notches 96 of seats 74 in order to releasably hold the valve seats in their proper position. Skirts 110 fit closely within body cavity 24 and engage body 12 to prevent the skirts from rotating. 
     Valve 10 is constructed by forming passage 13 through body 12 to provide the flow passage of the valve. Seat pockets 76 and the undercut grooves 78 are then formed about the flow passage, and the cylindrical body cavity 24 is bored through the body to intersect with passage 13 and with each undercut groove 78 in order to form openings 80. It should be pointed out that cavity 24 can be formed first, followed by formation of the flow passage and the seat pockets and undercut grooves. In any event, body cavity 24 intersects with each undercut groove 78 at two diametrically opposed locations in order to form the openings 80 which provide access to grooves 78. This manner of forming openings 80 is preferred because the openings and body cavity 24 are formed in a single operation rather than requiring cutting of the body cavity followed by another operation to form the openings to the undercut groove, such as cutting slots or other passages extending between the body cavity and grooves 78. 
     After valve body 12 has been formed, seats 74 are installed by inserting them into body cavity 24 and aligning lugs 90 with openings 80. Each valve seat 74 is inserted into its seat pocket 76 with lugs 90 passing through openings 80 into undercut groove 78. Each valve seat is thereafter rotated to move lugs 90 into groove 78 and out of alignment with openings 80. Preferably, rotation of each valve seat 74 is carried out by applying bar 100 to the seat with pegs 102 entering openings 98. Handle 104 is then attached to bar 100 and rotated to effect rotation of the seat in its seat pocket. As is apparent in FIG. 6, progressive rotation of seat 74 in the direction of the arrow causes surface 92 of each lug 90 to cam against surface 82 of groove 78 in wedging fashion to more tightly lock the lugs in the groove in response to progressive rotation of the valve seat. Consequently, increased rotation of each seat 74 locks it in its seat pocket more firmly due to the increased wedging action of lugs 90 in groove 78. In addition, the increased wedging action causes crush ring 88 to be more tightly pressed against surface 84 with progressive seat rotation. 
     When each seat 74 has been rotated far enough to lock it firmly in place in its seat pocket 76, seat skirts 110 are fitted on the seat with pins 114 of the skirts entering notches 96 of the valve seats. The interaction between pins 114 and notches 96 forms a detent mechanism for each seat 74 which prevents the seat from rotating inadvertently. Seat skirts 110 thus maintain lugs 90 out of alignment with openings 80 in order to positively lock seats 74 in their seat pockets 76. 
     During service of the valve, gate assembly 26 is moved between the open position shown in FIG. 1 and a closed position wherein fluid flow from passage 14 to passage 16 is precluded. When the handwheel or other operator (not shown) moves stem 46 upwardly toward the open position of FIG. 1, segment 30 contacts a stop in the valve body to prevent further upward movement of the segment. Continued upward movement of gate 28 causes the lower inclined surfaces 36 to cam against one another in a manner to expand the gate assembly outwardly such that surfaces 38 and 40 seal tightly against the seating surfaces 86 of valve seats 74, or against seal rings 87 if provided. When the gate assembly is fully open in the position of FIG. 1, its port 32 is aligned with passages 14 and 16 to provide a continuous flow passage through the valve. 
     Movement of gate 28 downwardly from the fully open position causes surfaces 36 to slide against one another, with assistance from springs 42, until the gate assembly 26 is in a fully collapsed condition wherein surfaces 38 and 40 are out of contact with seats 74 inwardly thereof. Springs 42 hold the gate assembly in its fully collapsed condition as it moves downwardly from the open position toward the closed position. Downward movement of the gate assembly eventually results in the bottom of segment 30 contacting a stop which prevents further downward movement of the segment. Continued downward movement of gate 28 causes the upper inclined surfaces 34 to slide against one another in camming fashion such that gate assembly 26 is fully expanded when it reaches a fully closed position blocking flow between passages 14 and 16. In the fully closed position of the valve, gate assembly 26 is fully expanded and surfaces 38 and 40 tightly seal against seating surfaces 86 of the valve seats, or against seal rings 87 if provided. When the gate assembly is moved upwardly from the closed position toward the open position, springs 42 maintain it in its collapsed condition until the open position is reached, at which time the gate assembly expands in the manner described previously. 
     Gate assembly 26 is thus in its fully expanded condition in both the open and closed positions of the valve, and it is maintained in a fully collapsed condition when it is between the open and closed positions. Since valve seats 74 are firmly locked in place, they do not bind against gate assembly 26 in the collapsed condition thereof, and the gate assembly can thus be easily moved between the open and closed positions without excessively dragging against the valve seats. 
     Despite the tight fit of lugs 90 in the undercut grooves 78, each valve seat 74 is able to pivot to a limited extent about a pivot axis defined by a line extending between the lugs along a diameter of the valve seat. Such pivotal movement of the valve seats provides them with enough play to effectively seal against surfaces 38 and 40 of the gate assembly, even when there is lack of parallelism or other imperfections or irregularities in the faces of the gate assembly or seats. The pivotal motion permitted the seats thus allows them to sealingly accommodate the gate mechanism while compensating for any irregularities therein. 
     As an alternative to a tight, wedging fit of lugs 90 in grooves 78 with a limited pivotal action, it is contemplated that the lugs will fit loosely in the undercut annular grooves in some situations in order to permit seats 74 to &#34;float&#34; in an axial relation to a limited extent toward and away from the gate assembly. Such a loose fit of lugs 90 in grooves 78 permits the seats to move to a greater extent than does a tight fit; consequently, a loose fit can compensate for more severe irregularities in the contact faces of the gate assembly and seats. Even when a loose fit is provided, the inside surface 92 of each lug should contact surface 82 of groove 78 before seats 74 can float inwardly far enough to drag excessively against the gate assembly in the collapsed condition thereof. Accordingly, the seats are able to accommodate the gate mechanism without binding excessively against it during movement between the open and closed positions. It is noted that the fit of pins 114 in notches 96 locks seats 74 against rotation without significantly hampering their floating movement toward and away from the gate mechanism 26, due to the ability of notches 96 to move axially along pins 114. 
     Valve seats 74 can be removed for repair or replacement simply by rotating them until lugs 90 line up with openings 80 and then pulling the seats inwardly into body cavity 24. Rotation of the seats is preferably accomplished by applying bar 100 to them and rotating the bar by means of the detachable handle 104. It is thus apparent that the seats can be quickly and easily removed in the field and repaired or replaced without requiring shop facilities or highly skilled service personnel.