GB2176576A - Gate valve - Google Patents

Abstract

A gate valve includes a rotating valve stem (50) carried by a bonnet assembly for actuation of a gate member (40). A fusible stem ring (126) supports the valve stem at an outer portion thereof within a thrust bearing chamber (56) of the bonnet assembly. The valve stem (50) moves axially outward from the valve chamber (20) when the fusible stem ring (126) melts due to an external fire condition to bring a valve stem backseat portion (64) into sealing engagement with a bonnet seat portion (54). The valve stem (50) moves axially outward from the valve chamber (20) independently of the bearing means (74, 76, 78) so that there exists no possibility of the bearing means becoming cocked or wedged against the valve stem to prevent rotation of the valve stem after the fire condition ceases to exist. <IMAGE>

Description

SPECIFICATION Gate valves This invention relates generally to fire-safe, non-rising stem type gate valves and, more specifically, to such a fire-safe gate valve having a fusible body or bodies which upon melting, permit the stem to rise relative to the bonnet to provide a metal-to-metal backseat therebetween.

Gate valves, both slab type and expanding type, are used in the pipeline industry to control fluid flow in oil and gas pipelines. Such valves are provided with packing assemblies which work well in maintaining the integrity of the valve under ordinary circumstances, but which are subject to being damaged should there be a fire, the heat of which engulfs the valve for more than a short period of time.

Accordingly, gate valves have been constructed which provide a metal-to-metal backseat seal between the stem and valve bonnet which are normally kept in a spaced relationship to one another by using one or more fusible bodies. If a fire occurs subjecting the valve to sufficient heat to melt the fusible materials, the valve components are permitted to shift allowing the metal-to-metal backseat to complete a seal. Example of gate valves utilizing fusible materials to provide a back-set are shown in the following table of U.S. patents 3771540, 3788600,3842854, 3896835, 4214600, 4245661, 4289157.

However, in most of the above U.S. patents, the fusible materials are positioned above the stem bearings relative to the flow passage of the valve. In this position when the fusible material melts the bearings and valve stem will be forced upwardly or outwardly from the flow passage by the pressurized fluid existing therein. Thus, the stem is allowed to back-seat against the valve bonnet to provide sealing protection for the packing assembly and upper bonnet areas of the valve. However, since the bearings are allowed to move with the stem, there exists the possibility that the bearings will become cocked or wedged against the stem, thereby making it difficult or impossible to cycle the valve after the fire has been extinguished.

Furthermore, in the prior art patents listed above, the valve stem and gate member are connected so that when the fusible material melts and vacates its cavity the gate member will shift with the valve stem to provide the backset seal with the valve bonnet. However, pressurized fluid in the upstream flowline continually acts on the gate member when it is in the closed position to create a drag force on the face thereof which impedes any upwardly or outwardly movement of the gate member.

Accordingly, the valve stem can be prevented from backseat sealing with the bonnet assembly due to its connection with the gate member and, thus, the packing assembly will be subjected to the highly pressurized fluid existing within the valve during a fire condition. Additionally, the packing assembly may deteriorate due to the extreme heat cuased thereby and flowline fluid will then leak exteriorly of the valve to further fuel the fire condition occurring exteriorly of the valve. Therefore, it is of beneficial value to have a gate valve with a heat responsible backseat which allows the valve stem to backseat with the bonnet assembly independently of the gate member.

It is, therefore, the object of this invention to provide an improved heat responsive backseat for gate valves which overcomes the aforementioned disadvantages of the prior art devices.

According to the invention, a gate valve comprises a valve body having an open ended valve chamber and inlet and outlet fluid passages communicating with the valve chamber, a gate member disposed in the valve chamber and movable between open and closed positions relative to the fluid passages to control fluid flow through the valve, a bonnet assembly forming a closure for the valve chamber and having a central bore with a seat portion facing in a direction toward the valve chamber, a rotatable normally non-rising valve stem extending through the central bonnet bore and threadedly engaging the gate member, the valve stem having an upwardly facing backseat portion within the valve chamber being normally in a spaced relationship to the bonnet seat portion and a reduced diameter portion defining an upwardly facing stem shoulder and spaced from the backseat portion in a direction away from the valve body, packing means positioned in the central bonnet bore for sealing between the valve stem and bonnet assembly and spaced from the bonnet seat portion in a direction away from the valve body, bearing means surrounding the valve stem and positioned further away from the valve body than the packing means and surrounding the reduced diameter portion and stem shoulder of the valve stem for supporting and providing rotation of the valve stem within the gate valve and a fusible stem spacing element of a preselected temperature degradable material positioned between the stem shoulder of the valve stem and the bearing means for normally maintaining the valve stem in a fixed axial position relative to the bearing means and bonnet assembly and normally maintaining the valve stem backseat portion in a spaced relationship from the bonnet seat portion, the fusible stem spacing element being adapted to relax its spacing function upon reaching the preselected temperature condition so that the valve stem is free to move axially relative to the bearing means and bonnet assembly such that the valve stem backseat portion sealingly contacts the bonnet seat por tion to provide a metal-to-metal backseat seal between the valve stem and bonnet assembly, whereby failure of the packing means at a temperature above the preselected temperature of the fusible spacing element will not result in fluid leakage around the valve stem to the exterior of the gate valve.

In the accompanying drawings: Fig. 1 is a part sectional side elevation of a normally non-rising stem type gate valve in accordance with the invention; Fig. 2 is a part sectional view to an enlarged scale of part of the valve of Figure; Figs. 3 and 4 are similar to Fig. 2 showing parts of the valve in alternative positions; Fig. 5 is a part sectional side elevation of an expanding gate valve shown in the open position; and Fig. 6 is a part sectional view to an enlarged scale of the valve of Fig. 5.

Referring to the drawings and specifically to Fig. 1, a normally non-rising stem type slab gate valve for use in pipelinese or related installations is illustrated and indicated generally at 10. The valve 10 includes a valve body 12 and bonnet assembly 14 which is attached to an upper flange portion 16 (in the orientation shown in the drawing) of valve body 12 by a plurality of bolts 18. A sealing member 22 is positioned in an annular groove 24 defined between valve body 12 and bonnet assembly 14 and seals therebetween. Valve body 12 has inlet and outlet fluid passages 26 and 28, respectively, which are in fluid communication with a valve chamber 20. Valve body 12 is provided with connection flanges 30 at the outer ends of passages 26 and 28 relative to valve chamber 20 for connecting the valve 10 into a fluid carrying pipeline or similar installation.

A pair of annular seat members 32 and 34 are retained in generally parallel annular seat recesses 36 and 38 respectively, which are disposed about flow passages 26 and 28 respectively, adjacent valve chamber 20. A gate member 40 is disposed between seat members 32 and 34 for reciprocal movement within valve chamber 20. Gate member 40 is movable from a position in which a port 42 extending through gate 40 is in registry with fluid passages 26 and 28 to a position blocking fluid flow through said fluid passages.

Valve body 12 defines a gate stop surface 44 against which the bottom of gate member 40 rests when the valve is closed to prevent further downward movement of the gate member 40.

The bonnet assembly 14 has an upwardly extending projection 46 in which is formed a longitudinal passage 48 for receiving a nonrising valve stem 50. The lower end of passage 48 communicates with valve chamber 20 and has a central projection 52 extending therein adjacent the passage opening to the valve chamber to provide a frusto-conical seat portion 54 facing the valve chamber. The upper end of passage 48 opens into an enlarged bearing chamber 56 which is threaded at its upper or outer end 58. The valve stem 50 is normally longitudinally fixed within passage 48 with its lower end section extending into valve chamber 20. The lower valve stem end section includes an externally threaded portion 60 to provide a connection with gate member 40 via a stem connection means 62, and an upwardly facing frusto-conical backseat portion 64 which is adjacent the the threaded end section 60.This tem backseat portion 64 is normally held in a position spaced from bonnet assembly seat portion 54. The valve stem 50 further includes a reduced diameter portion 66 defining an upwardly facing stem shoulder 68 and an externally threaded portion 70 located adjacent and above the reduced diameter portion 66. The reduced diameter portion 66 and threaded portion 70 are longitudinally positioned within the enlarged bearing chamber 54 with a support plate 72 being located at the bottom of this chamber surrounding the valve stem 50. Upper and lower thrust bearings 74 and 76, respectively, are positioned within the bearing chamber surrounding the valve stem 50 with the lower bearing 76 resting on support plate 72.The bearings 74 and 76 are separated by an annular spacer 78 which has an inwardly extending flange 80 intermediate its end defining upper and lower support shoulders 82 and 84 respectively. The upper support shoulder 82 supports a lock nut 86 which is threaded on the externally threaded portion 70 of valve stem. A key 88 rotationally locks the valve stem 50 to spacer flange 80. A packing retainer 90 and cover plate 92 are threadably received in the upper end of the bearing chamber 56, the packing retainer being installed first and, after its adjustment, the cover plate. Thrust bearings 74 and 76 may be of the permanent or sealed type or lubrication may be effected by introducing lubricant through a fitting 94. The upper end section of valve stem 50 extending above the bonnet assembly 14 is tapered and terminates in the reduced diameter threaded section 96. A handwheel 98 fits over the tapered portion of stem 50 and is secured thereto by nut 100.

Stem passage 48 further defines an annular packing chamber within the bonnet assembly 14 and a packing assembly 102 is disposed in the chamber to provide a fluid-tight seal between the valve stem 50 and bonnet assembly 14. Packing assembly 102 may include any of a number of commercially available packing materials which may be introduced into the packing chamber via a packing fitting 104 extending radially from the packing chamber to the outside of the bonnet assembly 14.

The stem connection means 62 provides a structure to connect the lower end of the valve stem 50 to an upwardly extending integral extension 106 of gate member 40. The gate member extension 106 is externally threaded as indicated at 108 and has a longitudinal bore 110 in which the threaded valve stem end section 60 is received. The gate member extension further includes a pair of aligned slots 112 formed in its upper end.

The stem connection structure further includes a stem nut 114 which is threadably received on the valve stem and section 60. The stem nut 114 includes a pair of ears 116 which depend downwardly from the stem nut 114 and are received in the corresponding gate member slots 112. The engagement between ears 116 and the sides of slots 112 prevents stem nut 114 from rotating relative to gate member 40 so that the rotary movement of valve stem 50 is translated to vertical movement of gate member 40. A gate nut 118 of cylindrical cup shape is threadably received onto the gate member extension 106 surrounding valve stem 50 and enclosing the stem nut 114. The top portion of the gate nut 118 has an opening 120 of larger diameter than the diameter of valve stem 50, but smaller in diameter than the outer diameter of stem nut 114.This particular size relationship betwteen the gate nut opening 120, the valve stem 50 and the stem nut 114 allows gate nut 118 to loosely fit about valve stem 50 when gate nut 118 is attached to gate member extension 106 while simultaneously holding stem nut 114 in position on the stem.

Gate nut 118 further includes an outwardly extending shoulder stop 122 which can contact bonnet assembly 14 to limit the upward movement of the gate member 14.

The gate valve 10 is normally a non-rising stem gate valve wherein the main seal between the valve chamber 20 and the external environment where the valve stem 50 penetrates the bonnet assembly, is conventionally provided by the packing assembly 102 as discussed above. However, should there be a fire in the vicinity of the gate valve 10 there exists the possibility that the packing assembly 102 may be destroyed. Therefore, it is desirable to provide a gate valve with a secondary sealing system which will allow the normally non-rising valve stem to rise slightly to provide a metal-to-metal backseat seal between the valve stem and the bonnet assembly in case the gate valve is ever subjected to the extreme heat of a fire condition.

As shown in Fig. 2, such a heat responsive backseat is provided in gate valve 10 between the valve stem backseat portion 64 and the bonnet seat portion 54. The valve stem 50 is longitudinally fixed in place by use of a body 126 of fusible material which is fashioned in the shape of a ring and is positioned within the annular space between the lower support shoulder 84 of annular spacer 78 and the top of the lower thrust bearing 76 surrounding the reduced diameter portion 66 of valve stem 50. A pair of washers 128 and 130 are positioned above and below the fusible ring 126 such that the upwardly facing valve stem shoulder 68 contacts the lower washer 130.

The longitudinal position of the valve stem 50 is fixed by threading lock nut 56 tightly onto the valve stem externally threaded portion 70 which in turn raises the valve stem 50 until the stem shoulder 68 solidly contacts the washer 130 and fusible material 126. Such fusible material is preferably a eutectic material having a melting point sufficiently above normal ambient temperatures to provide adequate support for the valve stem shoulder 68 under all normal conditions and, yet, melt promptly when the gate valve is exposed to a fire condition. When the fusible ring 126 melts, the material forming the ring is drained and/or otherwise expelled from its position supporting valve stem 50 to the exterior of annular spacer 78 through drain holes 132 to assure that the fusible material does not become trapped and continue to maintain its support of stem shoulder 68 and valve stem 50.This assures that valve stem 50 is free to move axially to provide the metal-to-metal backseat seal between the stem backseat portion 64 and the bonnet seat portion 54. The pressure within the valve chamber 20 acts on the stem to urge it upwardly or outwardly until such a backseat seal is obtained.

Referring to Fig. 4, a portion of the gate valve is shown with the valve stem 50 in the outward or back seated position. The fusible ring 126 has melted and exited by drain holes 132 and the valve stem 50 has been forced outwardly by fluid pressure within valve chamber 20 to provide the backseat as discussed above. This prevents fluids flowing through fluid passages 26 and 28 escaping around valve stem 50 when packing assembly 102 is destroyed or damaged by excessive heat. As shown in Fig. 4, the thrust bearings 74 and 76 and annular spacer 78 do not move axially with respect to the valve stem 50 upon melting of the fusible ring 126.This is an important feature of the present invention since in a majority of the prior valves the body of fusible material is positioned above the bearing means such that upon melting the bearings are allowed to move axially with the valve stem to provide a backseat, and this causes difficulties in cycling the valve after the fire condition has passed because the bearing means may become cocked or wedged within the bearing chamber thus preventing easy rotation of the valve stem to open or close the valve. In the present arrangement, the particular placement of the fusible ring 126 allows the valve stem 50 to move axially upward with respect to bearings 74 and 76 which remain stationary to provide a valve stem that may still be easily rotated after the fire condition has passed.

The gate valve illustrated in Figs. 1-4, includes the shoulder stop 122 extending radially from gate nut 118 to limit the upward movement of gate member 40. When the gate member is in its upper limit position with stop 122 contacting bonnet assembly 14, as shown in Fig. 2-3, the valve stem 50 and backseat portion 64 cannot rise sufficiently to provide a metal-to-metal seal with the bonnet seat portion 54. Accordingly, a second fusible gate ring 134 has been provided within gate nut 118 so that upon melting of ring 134 the valve stem 50 will move upwardly independently of the gate nut 118 and gate member 40. The fusible gate ring 134 is positioned between the upper surface of stem nut 114 and the lower inside surface of gate nut 118 surrounding the lower valve stem portion 60.

The ring 134 has a larger diameter than the diameter of opening 120 in gate nut 118 such that the ring 134 supports gate nut 118 and gate member 40 on stem nut 114. It may be necessary to provide a bearing washer 136 between ring 134 and gate nut 118 to better transmit the load of gate member 40 across the entire surface of fusible gate ring 134.

Referring to Fig. 3, upon the occurrence of a fire condition which radiates extreme heat the fusible stem and gate rings 126 and 134 respectively, will melt vacating their respective positions supporting the valve stem 50. Thus, valve stem 50 will move axially upward under fluid pressure from within the valve chamber to provide the metal-to-metal backseat between valve stem backseat portion 64 and bonnet seat portion 54 independently of the bearings 74 and 76 and the gate member 40.

Furthermore, the use of the fusible ring 134 within the stem connection means 62 provides benefits to the gate valve even when the gate member is not in its maximum upward position. As shown in Fig. 4, when the gate member 40 is in the closed or downward position, the sealing by the heat responsive backseat can be effected without the use of fusible gate ring 134 because gate nut stop 122 will not contact the bonnet assembly 14 upon the melting of fusible stem ring 126.

However, when the gate member 40 is in the closed position the pressurized fluid in the upstream inlet fluid passage 26 creates a drag force which acts on the face of gate member 40 to impede the normal movement of the gate member from its closed to open positions. In a fire situation, the internal pressures within the gate valve increase dramatically to create even larger drag forces acting on the gate member. Therefore, upon the melting of the fusible stem and gate rings 126 and 134, respectively, the valve stem 50 will backseat with bonnet assembly 14 completely independent of the gate member 40 so that gate drag will not affect actuation of the heat response backseat.

The heat responsive backseat can also be applied to a gate valve having an expanding type gate member as illustrated in Figs. 5 and 6 and indicated at 140. Since the two types of gate valves are very similar in construction, the reference numerals used for like parts in the expalnding gate valve will not change from those of the slab gate valve except that an "A" will be placed thereafter. Valve 140 is comprised of a valve body 1 2A and a bonnet assembly 1 4A which is attached to an upper flange portion 16A of valve body 12A bya plurality of bolts 18A. Bonnet assembly 14A forms a closure for an open ended valve chamber 20A defined by the annular flanged portion 16A. A sealing member 22A is positioned in annular groove 24A defined between valve body 12A and bonnet assembly 14A and seals therebetween.Valve body 12A has inlet and outlet fluid passages 26A and 28A respectively, which are in fluid communication with valve chamber 20A. Valve body 12A is provided with connection flanges 30A at the outer ends of passages 26A and 28A relative to valve chamber 20A for connecting gate valve 140 into a fluid carrying pipeline or similar installation.

A pair of annular seat members 32A and 34A are retained in generally parallel annular seat recesses 36A and 38A respectively, which are disposed about flow passages 26A and 28A respectively, adjacent valve chamber 20A. An expanding gate assembly 142 is disposed between seat members 32A and 34A for reciprocal movement within valve chamber 20A and includes a gate element 144 and a complementary segment 146. Gate element 144 has a V-shaped recess 148 and segment 146 has a V-shaped face 150. The V-shaped recess and face complement each other so that the V-shaped face 150 fits within recess 148 when gate element 144 and segment 146 are in a fully collapsed position. A pair of springs 152, one on each side of gate assembly 142, extend between the sides of gate element 144 and segment 146 for continuously urging them into their fuily collapsed position.

When the gate valve 140 is in a closed position (not shown) ports 154 and 156 are not aligned with flow passages 26A and 28A, and the gate assembly is interposed between the flow passages to block flow of fluid through the gate valve.

The bonnet assembly 14A has an upwardly extending projection 46A in which is formed a longitudinal passage 48A for receiving a nonrising valve stem 50A. The lower end of passage 48A communicates with valve chamber 20A and has a central projection 52A extending therein adjacent the passage opening to the valve chamber to provide a frusto-conical seat portion 54A facing the valve chamber.

The upper edge of passage 48A opens into an enlarged bearing chamber 56A which is threaded at its upper or outer end 58A. The valve stem 50A is normally longitudinally fixed within passage 48A with its lower end section extending into valve chamber 20A. The lower valve stem end section includes an externally threaded portion 60A to provide a connection with gate member 40A via a stem connection means 62A, and an upwardly facing frusto-conical backseat portion 64A which is adjacent the threaded end section 60A. The stem backseat portion 64A is normally held in a position spaced from bonnet assembly seat portion 54A. The valve stem 50A further includes a reduced diameter portion 66A defining an upwardly facing stem shoulder 68A, and an externally threaded portion 70A located adjacent and above the reduced diameter portion 66A.The reduced diameter portion 66A and threaded portion 70A are longitudinally positioned within the enlarged bearing chamber 54A with a support plate 72A being located at the bottom of this chamber surrounding the valve stem 50A. Upper and lower thrust bearings 74A and 76A respectively, are positioned within the bearing chamber surrounding the valve stem 50A with the lower bearing 76A resting on support plate 72A. The bearings 74A and 76A are separated by an annular spacer 78A which has an inwardly extending flange 80A intermediate its end defining upper and lower support shoulders 82A and 84A, respectively. The upper support shoulder 82A supports a lock nut 86A which is threaded on the externally threaded portion 70A of valve stem 50A and a key 88A rotationally locks the valve stem 50A to spacer flange 80A.A packing retainer 90A and cover plate 92A are threadably received in the upper end of the bearing chamber 56A, the packing retainer being installed first and, after its adjustment, the cover plate being installed. The thrust bearings 74A and 76A may be of the permanent or sealed type or lubrication may be effected by introducing lubricant through a fitting 94A. the upper end section of valve stem 50A extending above the bonnet assembly 14A is tapered and terminates in the reduced diameter threaded section 96A. A handwheel 98A fits over the tapered portion of stem 50A and is secured thereto by nut 100A.

Stem passage 48A further defines an annular packing chamber within bonnet assembly 14A and a packing assembly 102A is disposed within this chamber to form a fluid-tight seal between the valve stem 50A and bonnet assembly 14A. Packing assembly 102A may include any of a number of commercially available packing materials which may be introduced into the packing chamber via a packing fitting 104A extending radially from the packing chamber to the outside of the bonnet assembly 14A.

The stem connection means 62A provides a structure to connect the lower end of the valve stem 50A to an upwardly extending integral extension 158 of gate assembly 142.

The gate assembly extension 158 is externally threaded as indicated at 160 and has a longitudinal bore 162 in which the threaded valve stem end section 60A is received. The gate member extension further includes a pair of aligned slots 164 formed in its upper end.

The stem connection structure further includes a stem nut 11 4A which is threadably received on the valve stem end section 60A. The stem nut 1 14A includes a pair of ears 1 16A which depend downwardly from the stem nut 11 4A and are received in the corresponding slots 164. The engagement between ears 11 6A and the sides of slots 164 prevents stem nut 114 from rotating relative to gate assembly 142 so that the rotary movement of valve stem 50A is translated to vertical movement of gate assembly 142. A gate nut 1 18A of cylindrical cup shape is threadably received onto the gate assembly extension 158 surrounding valve stem 50A and enclosing the stemnut 114A.The top portion of the gate nut 1 18A has an opening 120A of larger diameter than the diameter of valve stem 50A, but smaller in diameter than the diameter of stem nut 114A. This particular size relationship between the gate nut opening 120A, the valve stem 50A and the stem nut 1 14A allows gate nut 11 8A to loosely fit about valve stem 50A when gate nut 11 8A is attached to gate assembly extension 158 while simultaneously holding stem nut 1 14A in position on the stem.

The heat responsive backseat is the same for both the siab and expanding type of gate valve. As is illustrated in Fig. 6, the gate valve 140 is normally a non-rising stem expanding gate valve wherein the main seal between the valve chamber 20A and the external environment where the valve stem 50A penetrates the bonnet assembly is conventionally provided by the packing assembly 102A as discussed above. However, should there be a fire in the vicinity of the gate valve 140 there exists the possibility that the packing assembly 102A will be destroyed.

A metal to metal seal is provided in gate valve 140 between the valve stem backseat portion 64A and the bonnet seat portion 54A.

The valve stem 50A is longitudinally fixed in place by use of a body of fusible material 126A which is fashioned in the shape of a ring and is positioned within the annular space between the lower support shoulder 84A of annular spacer 78A and the top of the lower thrust bearing 76A surrounding the reduced diameter portion 66A of valve stem 50A. A pair of washers 128A and 130A are positioned above and below, respectively, the fusible ring 1 26A such that the upwardly facing valve stem shoulder 68A contacts the lower washer 130A. the longitudinal position of the valve stem 50A is fixed by threading lock nut 86A tightly onto the valve stem externally threaded portion 70A which in turn raises the valve stem 50A until the stem shoulder 68A solidly contacts the washer 1 30A and fusible material 126A.When the fusible ring 1 26A melts it is drained and/or otherwise expelled from its position supporting valve stem 50A, to the exterior of annular spacer 78A through drain holes 132A to assure that the fusible material does not become trapped and continue to maintain its support of stem shoulder 68A and valve stem 50A. This assures that valve stem 50A is free to move axially to provide the metal-to-metal backseat seal between the stem backseat portion 64A and the bonnet seat portion 54A. The pressure within the valve chamber 20A acts on the stem to urge it upwardly or outwardly until the seal is effected.

However, due to the natuie of expanding type gate valves, it is important that the valve stem 50A be able to rise sufficiently to provide the backseat seal independently of the gate assembly 142. Therefore, fusible gate ring 1 34A has been provided within gate nut 1 18A so that upon melting of ring 134A the valve stem 50A will move axially upward independently of the gate nut 11 8A and gate member 142. The fusible gate ring 134A is positioned between the upper surface of stem nut 1 14A and the lower inside surface of gate nut 11 8A surrounding the lower valve stem portion 60A.The ring 134A has a larger diameter than the diameter of opening 120A in gate nut 1 18A such that the ring 134A supports gate nut 188A and gate assembly 142 on stem nut 114A. It may be necessary to provide a bearing washer 136A between ring 134A and gate nut 1 18A to better transmit the load from gate assembly 142 across the entire surface of fusible gate ring 134A. Referring to Fig. 6, upon the occurrence of a fire condition which radiates extreme heat, the fusible stem and gate rings 126A and 134A, respectively, will melt vacating their respective positions supporting the valve stem 50A.

Thus, the valve stem will move axially upward under fluid pressure from within the valve chamber to provide the metal-to-metal backseat between valve stem backseat portion 64A and bonnet seat portion 54A independently of the bearings 74A and 76A and the gate assembly 142.

The designs described allow the valve stem to form a backseat seal with the bonnet assembly independently without axial movement of the bearing members so that it is impossible for the bearing members to become cocked or wedged within the bearing chamber and against the valve stem to inhibit later rotation of the valve stem. Furthermore, the valve stem moves axially independently of the gate member so that gate drag does not affect the upward movement of the valve stem.

The non-rising stem type slab gate valve has been illustrated with a gate stop to limit the upward movement of the gate member relative to the bonnet assembly. However, such a gate stop could be eliminated so that the valve stem would move axially upward relative to the bonnet assembly upon melting of only the fusible stem ring. In such a valve, the fusible gate ring would be unnecessary to provide the backseat seal betwteen the valve stem and bonnet assembly, unless, gate drag was seen to represent a significant problem due to the particular use contemplated.

Claims (12)

1. A gate valve comprising a valve body having an open ended valve chamber and inlet and outlet fluid passages communicating with the valve chamber, a gate member disposed in the valve chamber and movable between open and closed positions relative to the fluid passages to control fluid flow through the valve, a bonnet assembly forming a closure for the valve chamber and having a central bore with a seat portion facing in a direction toward the valve chamber, a rotatable normally non-rising valve stem extending through the central bonnet bore and threadedly engaging the gate member, the valve stem having an upwardly facing backseat portion within the valve chamber being normally in a spaced relationship to the bonnet seat portion and a reduced diameter portion defining an upwardly facing stem shoulder and spaced from the backseat portion in a direction away from the valve body, packing means positioned in the central bonnet bore for sealing between the valve stem and bonnet assembly and spaced from the bonnet seat portion in a direction away from the valve body, bearing means surrounding the valve stem and positioned further away from the valve body than the packing means and surrounding the reduced diameter portion and stem shoulder of the valve stem for supporting and providing rotation of the valve stem within the gate valve and, a fusible stem spacing element of a preselected temperature degradable material positioned bettween the stem shoulder of the valve stem and the bearing means for normally maintaining the valve stem in a fixed axial position relative to the bearing means and bonnet assembly and normally maintaining the valve stem backseat portion in a spaced relationship from the bonnet seat portion, the fusible stem spacing element being adapted to relax its spacing function upon reaching the preselected temperature condition so that the valve stem is free to move axially relative to the bearing means and bonnet assembly such that the valve stem backseat portion sealingly contacts the bonnet seat portion to provide a metal-tometal backseat seal between the valve stem and bonnet assembly, whereby failure of the packing means at a temperature above the preselected temperature of the fusible spacing element will not result in fluid leakage around the valve stem to the exterior of the gate valve.

2. A gate valve as claimed in claim 1 further comprising a stem connection means positioned within the valve chamber for providing a connection between the threaded end section of the valve stem and the gate member including a pair of opposed slots on the upper end of the gate member, a stem nut threaded onto the end section of the valve stem and having a pair of ears fitting within the opposed slots, and an inverted cupshaped gate nut threaded onto the upper end of the gate member forming a chamber which enclosed the stem nut, the gate nut having an opening in its closed end which receives the valve stem therethrough, the chamber having a larger inside axial dimension than the axial dimension of the stem nut, whereby, rotation of the valve stem effects axial movement of the gate member between open and closed positions of the fluid passages, and a fusible gate spacing element of a preselected temperature degradable material positioned within the chamber between the stem nut and the closed end of the gate nut for normally maintaining the stem nut in a fixed relative axial position with respect to the gate nut and gate member, the fusible gate spacing element being adapted to relax its spacing function upon reaching the preselected temperature condition so that the stem nut and valve stem are free to move to a limited axial extent relative to the gate nut and gate member such that the valve stem backseat portion sealingly contacts the bonnet seat portion to provide a metal-tometal seal between the valve stem and bonnet assembly without having to overcome gate drag caused by the force of fluid flow in the fluid passages interacting on the gate member.

3. A gate valve as claimed in claim 2, wherein the stem connection means further comprises a shoulder stop on the exterior circumference of the gate nut which contacts the bonnet assembly when the gate member is in its open position with respect to the fluid passages to limit the upward axial movement of the gate nut and gate member relative to the bonnet assembly whereby upon melting of the fusible stem and gate elements the stem nut and valve stem are free to move to a limited axial extent relative to the gate nut and gate member to allow the valve stem backseat to sealingly contact the bonnet seat portion to provide a metal-to-metal seal between the valve stem and bonnet assembly.

4. A gate valve as claimed in claim 3, wherein the fusible spacing elements are eutetic metal alloys having a melting point sufficiently above the normal temperatures to which it is to be exposed in normal valve operations without having excessive deformation from compressive stress at such temperature and having a sufficiently low melting point to melt promptly when the valve is exposed to a fire condition.

5. A gate valve as claimed in claim 4, wherein the bonnet seat portion and the backseat portion of the valve stem are complementarily frusto-conical in shape.

6. A gate valve comprising a valve body having an open ended valve chamber and inlet and outlet fluid passages communicating with the valve chamber, a valve seat positioned about each said inlet and outlet fluid passages adjacent the valve chamber, a bonnet assembly forming a closure for the valve chamber and having a central bore therein communicating with the valve chamber, the central bore having a seat portion facing in a direction toward the valve chamber and an enlarged diameter bore portion axially spaced from the seat portion in a direction away from the valve body, a rotatable non-rising valve stem carried within the central bore of the bonnet assembly and having a threaded end section extending into the valve chamber a backseat portion positioned within the valve chamber which faces toward the bonnet assembly in normally spaced relationship to the seat portion of the bonnet assembly, and a valve stem shoulder positioned within the enlarged diameter bore portion of the central bore which faces in a direction away from the valve chamber, packing means positioned in the central bore of the bonnet assembly between the seat portion and enlarged diameter bore portion for sealing between the valve stem and the bonnet assembly, a gate member disposed in the valve chamber and movable between open and closed positions relative to the fluid passages to control fluid flow through the valve, the gate member having an externally threaded extension with a longitudinal bore therein receiving the threaded end section of the valve stem, stem connection means positioned in the valve chamber for providing a connection between the threaded end section of the valve stem and the gate member extension, bearing means positioned in axially fixed relationship within the enlarged bore portion of the central bonnet assembly bore for supporting and allowing rotation of the valve stem, and a fusible stem spacing element formed from a preselected temperature degradable material positioned between the valve stem shoulder and the bearing means for normally maintaining the valve stem in a fixed axial position relative to the bearing means and normally maintaining th valve stem backseat portion in spaced relationship relative to the bonnet seat portion, the fusible stem spacing element being adapted to relax its spacing function upon reaching the preselected temperature condition so that the valve stem is free to move to a limited axial extent relative to the bearing means to allow the valve stem backseat portion to sealingly contact the bonnet seeat portion thereby providing a metal-to-metal seal between the valve stem and bonnet assembly whereby failure of the packing means at a temperature above the presented temperature of the fusible element will not result in fluid leakage around the valve stem to the exterior of the gate valve.

7. A gate valve according to claim 6, in which the stem connection means comprises a pair of opposed slots on the upper end of the gate extension, a stem nut threaded onto the end section of the valve stem and having a pair of ears fitting within the opposed slots whereby rotation of the valve stem effects movement of the gate member between opoen and closed positions of the fluid passages, an inverted cup-shaped gate nut threaded onto the externally threaded gate member extension and forming a chamber which encloses the stem nut, the gate nut having an opening in its closed end to receive the valve stem, the chamber having a larger inside axial dimension than the axial dimension of the stem nut, and a fusible gate spacing element of a preselected temperature degradable material positioned within the chamber between the stem nut and the closed end of the gate nut for normally maintaining the stem nut in a fixed relative axial position with respect to the gate nut and gate member, the fusible gate spacing element being adapted to relax its spacing function upon reaching the preselected temperature condition so that the stem nut and valve stem are free to move to a limited axial extent relative to the gate nut and gate member so that the valve stem backseat portion sealingly contacts the bonnet seat portion to provide a metal-to-metal seal between the valve stem and bonnet assembly without having to overcome gate drag caused by the force of fluid flow in the fluid passages interacting on the gate member.

8. A gate valve according to claim 7, wherein the stem connection means further comprises a shoulder stop on the exterior circumference of the gate nut which contacts the bonnet assembly when the gate member is in its open position with respect to the fluid passages to limit the upward axial movement of the gate nut and gate member relative to the bonnet assembly whereby upon melting of the fusible stem and gate elements the stem nut and valve stem are free to move to a limited axial extent relative to the gate nut and gate member to allow the valve stem backseat to sealingly contact the bonnet seat portion to provide a metal-to-metal seal between the valve stem and bonnet assembly.

9. A gate valve according to claim 6 wherein the fusible spacing elements are formed from a eutectic metal alloy having a melting point sufficiently above the normal tempoeratures to which it is to be exposed in normal valve operations without having excessive deformation from compressive stress at such temperatures and having a sufficiently low melting point to melt promptly when the valve is exposed to a fire condition.

10. A gate valve according to claim 6, wherein the bonnet seat portion and the backseat portion of the valve stem are complementarily frusto-conical in shape.

11. A gate valve comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figures 1, 2, 3 and 4 of the accompanying drawings.

12. A gate valve comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figures 5 and 6 of the accompanying drawings.