GB2163530A - Ball valve - Google Patents

Abstract

A soft-seated fire-safe ball valve includes a pair of seat assemblies each comprising a seat ring (102), at least one ring (102) being cooperatively associated with a weir ring (130) for inhibiting extrusion of the seat ring (102) such that the seat assembly operates to maintain a fluid-tight seal upon partial destruction of the elastic seat ring due to elevated temperatures. <IMAGE>

Description

1 GB2163530A -1

SPECIFICATION

Ball valve This invention relates to ball valves and is 70 particularly applicable to fire-resistant or fire safe ball valves.

When employed in the valve art, the term -fire-safe- has come to mean a valve that satisfies certain specified conditions when subjected to a fire; see Arant, Fire-Safe Val ves-An Overview, Proceedings, ThirtySixth Annual Symposium on Instrumentation for the Process Industries (Texas A&M University, 1981). Unfortunately, different sets of condi tions have been promulgated by different or ganizations and the valve industry has not yet recognized a uniform standard. Basically, ac cording to one of the standards (American Pe troleum Institute 607), if a valve will substan tially maintain a fluid seal in a closed position at a valve body temperature of a least 593'C (1 100'F) for at least ten minutes, it may be certified as -fire-safe-. Valves which include design characteristics to resist leakage upon exposure to fire but cannot meet this standard are commonly referred to as -fire-resistant-.

The invention is particularly applicable to a new and improved soft-seated fire-safe ball valve and seat assembly for a valve of the type having a so-called -floating ball- and will be described with particular reference thereto.

However, it will become readily apparent to those skilled in the art that the invention is capable of broader applications and could be adapted for use in other types and styles of valves.

Ball valve constructions in commercial use typically employ annular seats or seat rings formed of a resilient and deformable plastic, such as Teflon (Registered Trademark) for sealing engagement with the ball. A pair of such seat rings is positioned respectively adja cent the valve inlet and outlet openings. The ball member itself is mounted for a slight amount of free movement or shifting axially of the seats under fluid pressure conditions when the ball member is in a valve-closed position.

Such shifting causes the ball member to act against and to flex and deform the down stream seat ring to enhance its sealing en gagement with the ball member. The amount of such flexing varies in accordance with the fluid pressure involved.

When subjected to a fire, the soft annular seat of a conventional floating-ball type of ball valve is substantially damaged by the heat of the fire to the extent that leakage through the valve may become unacceptable. Typically, downstream of the ball member, the sequence of seat destruction is such that the plastic first softens and beings to flow out or extrude through the valve port. Continued exposure to excessive heat ultimately causes the seat to char and sublimate or evaporate. The destruc- tion of the plastic seat allows the ball member to shift further under fluid pressure conditions until the ball member engages a secondary seat. Such a secondary seat typically comprises a metal or non-flammable radially inwardly extending projection of the valve body, such as a support shoulder for the plastic seat. Normally, such a surface is not specially designed for a high degree sealing engage- ment against the ball member and allows substantial leakage.

Another particular problem occurs where the plastic seat is only partially destroyed by a fire. For example, where a valve is exposed to radiant heat from a fire on one side only, or in a low intensity fire, only that portion of the valve seat nearest the fire may soften and extrude into the valve port. The ball member may then shift under fluid pressure towards that area made available to it by the extrusion and, being unable to evenly contact the secondary seat, expose a large leakage path. Alternatively, the ball member may be held back from making any contact with the secondary seat by the undestroyed portions of the plastic seat and similarly expose large leakage paths. Under either situation, fluid may rush through the leakage paths and quench the valve. The quenching action operates to pre- vent further deterioration of the seat in spite of a continuing fire and typically maintains a massive leak through the valve.

An additional but often unrecognized problem which occurs during a fire is the rapid increase in fluid pressure by heated fluid which is trapped between the inlet and outlet seats around the ball member. The heat of the fire may heat and even vapourize such fluid in the centre of the valve between the seats.

Often the fire is so intense that the fluid is so rapidly vapourized that it cannot escape past the seats quickly enough to prevent an excessive increase of pressure within the valve. Such an increase in pressure can easily ex- ceed the valve rating and rupture the seals at the stem packing and the body joints, or rupture the valve body itself.

Another practical problem occurs when a fire hose is trained upon a valve in a volatile liquid system which has been heated by a fire. The quick-cooling action of the hose water causes a violent condensation of heated vapour in the valve that dislodges the ball member and churns up char, waste and contami- nants that may become lodged between the ball member and the ball sealing surface and thereby provide additional leakage paths.

One overall objective of fire-resistant or firesafe ball valve seat designs is to obtain a valve which will seal with conventional valve seat materials at normal operating conditions and will also seal when subjected to a fire. Various forms and types of ball valve seat designs have heretofore been suggested and employed in the industry for purposes of ob2 GB2163530A 2 taining a fire-safe or fire-resistant ball valve, all with varying degrees of success. It has been found that the defects present in most prior fire-safe or fire-resistant ball valve designs are such that the devices themselves are of lim ited economic and practical value.

A common type of fire-resistant ball valve design includes a primary soft seat of a plas tic material, such as Teflon (Registered Trade Mark), and a secondary seat of metal or a high temperature composite material to seal the valve upon destruction of the primary seat in a fire. The secondary seat typically com prises a metal rim or washer interposed be tween the soft plastic primary seat and a 80 valve body support shoulder. This design suf fers from the problems naturally resulting from any type of metal-to-metal seal. Since the ball member in a floating ball type valve is never perfectly spherical and the secondary metal seat is not made perfectly circular, leakage across the secondary seal after destruction by fire of the primary seal is usually high, as the ball member cannot make a full annular con tact with the metal seat. For a metal-to-metal 90 seal to be anywhere near leak-tight in a fire safe or other application, the sealing surfaces must be match lapped or burnished, one into the other. Since such a procedure is very ex pensive, match lapping is an economically im- 95 practical procedure for a manufacturer of fire safe or fire-resistant ball valves. In addition, a match-fitted secondary seat would likely be marred by the hazards and consequences of normal valve operation, such as corrosion, pitting, scaling, erosion and the like, to the extent that, during a subsequent fire, the ad vantages of match fitting would have been lost. Ball valve designs incorporating the sec ondary metal seat or high temperature compo- 105 site seat also -suffer from the problems of par tial deterioration and quenching of the primary seat and the problems of loose and bocking char and waste materials associated with quick cooling.

A suggested improvement over the mere metal secondary seat design has been to add a secondary seat comprised of a heat-resis tant material which is more deformable and resilient than metal. Typically, carbon or graphite rings have been used. While such de signs may provide improved operation when new, it has been found that such designs are particularly susceptible to damage in normal service. Normal wear through cycling the valve, erosion while opening, or abrasion by foreign matter can easily damage the secon dary seat materials since they are typically brittle and of low strength compared with a normal plastic seat. Therefore, such designs usually still include a metal lip or rim as a final or tertiary seat to restrict leakage if the sec ondary seat is damaged. Such a multiplicity of seats increases the size, complexity, and cost of the valve without adding a reliable emer- gency seal, Whatever elements of wear, erosion or other foreign matter might damage one of the seats is likely to damage all of the seats since they are all equally exposed during normal service.

One alternative suggestion for obtaining a fire-safe valve is to include packing a conventional valve is enough insulation to insulate the valve for a sufficient amount of time to obtain a fire-safe rating. Another suggestion is to dispose a sprinkler near the valve which will quench the valve during a fire. Both of these designs are unsuitable for practical cost reasons in that they would involve expensive installations and maintenance. In addition, an insulated valve would suffer from the problem of uncertainty as to whether the insulation would be properly reattached or installed each time the valve underwent maintenance.

It has, therefore, been desired to develop a fire-safe ball valve and seat assembly which would operate satisfactorily at normal operating conditions and also seal the valve in a valve-closed position upon exposure to a fire. Preferably, such a design would eliminate the necessity for utilizing costly sprinklers or insulation packings to protect the valve.

The present invention contemplates a new and improved construction of ball valve which is capable of overcoming some or all of the above referred to problems and others. The invention further contemplates being useful with a wide variety of seat designs and materials which effectively seal at a wide variety 100 of normal operating conditions.

The present invention provides a ball valve including a body having a central passageway, a ball member having a fluid flow opening therethrough and being positioned in said central passageway and mounted for selective rotation between valve-open and valve-closed positions to control fluid flow through said valve,- a pair of radially inward extending shoulders in said central passageway disposed circumferentially thereof on opposite sides of said ball member, and a pair of seat assemblies disposed axially between said shoulders and said ball member, each of said seat assemblies comprising an elastic seat ring sup- ported in said central passageway for fluid sealing engagement with said ball member and a deformable, heat resistant secondary seat ring element interposed between said elastic seat ring and the respective shoulder, said secondary seat ring element being substantially isolated from normal service contact with the ball member and system fluid whereby, upon damage to said elastic seat ring by exposure to elevated temperatures, said secon- dary seat ring element engages said ball member to seal said valve.

Another object of the invention is the provision of a new and improved fire-safe ball valve and seat assembly which has improved fluid sealing characteristics upon exposure of 3 0 GB2163530A 3 v the valve to fire or heat.

Another object of the present invention is the provision of such a ball valve and seat assembly which will avoid metal-to-metal fluid 5. sealing engagements.

Still another object of the invention is the provision of a ball valve which will maintain fluid sealing upon partial or complete destruc tion by fire of a primary soft plastic seat member.

Yet another object of the invention is the provision of a ball valve seat assembly which will prevent the interposition of primary seat ring extrusions or fire-caused char and con taminants between the ball member and ball engaging and sealing surfaces.

Another object is the provision of a secon dary seat which will function upon fire damage to the ball valve regardless of the design and construction material of the primary seat. 85 Still another object is the provision of a sec ondary seat which will not deteriorate with age in normal service.

Another object is the provision of a fire-safe ball valve which prevents the accumulation of destructively high pressures within the valve body and seat assemblies when the valve is exposed to high temperatures.

Still another object is the provision of a ball valve seat assembly which includes a secon dary seat that is removed from the deteriora tion and wear forces of fluid flow associated with normal service.

More specifically, the invention includes a fire-safe ball valve comprising a body having a 100 central passageway; a ball member having a fluid flow opening therethrough and being po sitioned in said central passageway and mounted for selective rotation between valve open and valve-closed positions to control fluid flow through said valve; a pair of radially inward-extending shoulders being provided in said passageway disposed circumferentially thereof on opposite sides of said ball member and a pair of radially inward-extending coun terbores also being provided in said passage way disposed on opposite sides of said ball member; and a pair of composite seat assem blies positioned axially in said passageway on opposite sides of said ball member for fluid sealing engagement with said ball member, each of said seat assemblies comprising a re inforcing ring having a central opening and abutting an inner end wall of the respective counterbore, a seat ring abutting said reinforc ing ring and designed for elastic flexure gener ally towards and away from said reinforcing ring, said seat ring having a central opening and a ball-engaging surface facing said ball member for sealing engagement with said ball member, and a secondary seat ring interposed between said flexible seat ring and the respec tive shoulder, said secondary seat ring includ ing a disc spring having a central opening and a generally frusto-conical configuration in an unstressed condition and at least one annular sheet of expanded carbonaceous material disposed at a respective face of said disc spring, said ball member and said pair of composite seat assemblies being sized so that, upon damage to said seat ring caused by exposure of said valve to elevated temperatures, said secondary seat ring is urged into sealing engagement with said ball member.

In accordance with a preferred aspect of the present invention, the secondary seat ring comprises a disc spring in combination with a sheet of expanded carbonaceous material. The disc spring has a generally frustoconical confi- guration in an unstressed condition. The sheet of expanded carbonaceous material is generally radiaily coextensive with the disc spring and is interposed at least between the spring and the primary soft plastic seat ring. The disc spring operates to urge continuously the facing sheet of carbonaceous material and the soft seat ring towards the ball member. Upon damage to the primary seat ring by a fire, the facing sheet of carbonaceous material contacts the ball member to effect fluid sealing.

In accordance with another preferred aspect of the invention, the secondary seat ring includes a pair of sheets of expanded carbonaceous material. The pair sandwich the disc spring and are generally radially coextensive therewith. A first sheet faces the ball member for engagement with the ball member upon damage to the primary soft seat ring. A second sheet faces the respective radially inward extending shulder for sealing engagement with the shoulder upon damage to the primary seat ring.

According to a further aspect of the invention, a weir ring is included in a primary seat ring and is interposed generally between the primary seat ring and the secondary seat member.

According to another aspect of the present invention, the ball member includes a second opening normal to the principal fluid flow opening of the ball member. The second opening faces the valve inlet when the ball member is in the closed position to communicate fluid contained in the centre of the valve to the inlet fluid.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a longitudinal sectional view through a ball valve which incorporates a preferred embodiment of the invention; Figure 2 is an enlarged sectional view of a portion of the downstream seat assembly of Fig. 1 just prior to valve make-up and with the ball member omitted for ease of illustration; Figure 3 is an enlarged sectional view of a portion of the downstream seat assembly of Fig. 1, but with the valve in a closed position under the influence of elevated fluid system 4 GB2163530A 4 pressures; Figure 4 is a sectional view, similar to Fig. 3, but with the valve having been exposed to fire and heat such that the soft plastic seat ring has begun to flow outwardly through the valve port; Figure 5 is a sectional view, similar to Fig. 4, where the bail has made contact with the secondary seat; Figure 6 is a sectional view, similar to Figs. 4 and 5, where the soft plastic seat has been completely destroyed; Figure 7 is a plan view of the valve taken along lines 7-7 of Fig. 1 with a portion of the valve body broken away for showing an improved bolting arrangement; Figure 8 is an enlarged sectional view of a seat assembly which incorporates an alternative embodiment of the invention; Figure 9 is an enlarged sectional view of yet another alternative embodiment of the invention; Figure 10 is an enlarged sectional view of a seat assembly of a ball valve which incorpor ates another alternative embodiment of the invention; Figure 11 is an enlarged sectional view of still another alternative seat assembly embodiment which incorporates the invention; 30- Figure 12 is an enlarged perspective view of the seat assembly of Fig. 10 after partial de struction upon exposure to a fire and having been removed from the valve body for ease of illustration; and Figure 13 is an enlarged perspective view of 100 the seat assembly of Fig. 1 after partial de struction upon exposure to a fire and having been removed from the valve body for ease of illustration.

Referring now to the drawings wherein the showings are for purposes of illustrating the preferred and several alternative embodiments of the invention only and not for purposes of limiting the same, Fig. 1 shows a ball valve A having a pair of opposed seat assemblies B disposed on opposite sides of a floating type spherical ball member C.

More particularly, and with reference to Figs. 1 and 7, ball valve A includes a body or housing 10 having a main or central body sec- 115 tion 12 and opposed end fittings 14, 16. Seat assemblies B and ball C are mounted within the main body section 12 and the ball mem ber is arranged for selective rotation by a stem and actuating handle assembly 18. Ball member C includes a first or principal fluid flow opening 15 extending along the diameter of the ball for communicating fluid flow from the inlet to the outlet when the valve is in a valve-open condition. The ball C has a second opening 17 normal to the principal flow opening 15 and generally facing the valve inlet when the valve is in a closed position to communicate fluid and fluid pressure in the centre of the valve to the valve inlet fluid. Substan- tiaily all of the details of the portions of the valve illustrated in Fig. 1, except for the seat ring assemblies, may be modified as desired and/or necessary to accommodate different types or styles of ball valve constructions.

In general, however, and for purposes of describing the invention, the valve body includes a generally cylindrical central passageway or axiallyextending fluid flow opening 20 which is only slightly larger in diameter than ball member C. Each of the end fittings 14, 16 is releasably connected to central body section 12 by a plurality of longitudinally extending tie bolts 22 received through bolt bores 24 of opposed end fittings 14, 16 and fittedly received in main body section 12 (Fig. 7). It has been found that the use of a plurality of tie bolts 22 received in main body section 12 is particularly advantageous for a fire- safe application to avoid the problems of yielding or breaking of longer tie bolts which may occur after a valve has been heated in a fire and rapidly cooled with water from a fire hose or sprinkler. During a fire, the metal components of the valve will naturally expand upon being heated. When a fireman has trained a hose on such a heated valve, the periphery of the valve, including the tie bolts, will cool and will contract more quickly than the body of the valve. Such quick cooling and contraction may ultimately result in yielding or breaking of the tie bolts 22. Where a plurality of shorter, fitted tie bolts is employed, such problems are minimized. The end fittings 14, 16 are also provided with internal threads 26, 28 or any other convenient means to enable connecting of the valve to an associated fluid system or piping.

The stem and actuating handle assembly 18 illustrated includes a stem member 30 having a lower end 32 configured as shown for sliding receipt in a slot or groove 34 in the upper end of ball C. This arrangement allows the ball to be rotated between valve open and closed positions while, at the same time, permitting the ball to have some freedom of movement for shifting axially in valve body passageway 20 when the valve is in a closed position and fluid pressure is acting on the ball.

Stem member 30 extends outwardly through an opening 36 in central body section 12. Packing rings 38, 40, 42 suitable for elevated temperatures are positioned in opening 36 and sealingly engage the opening and stem mem- ber 30. As shown, lower packing ring 42 rests upon an inwardly extending flange 44 formed within opening 36. A thrust washer 46 suitable for elevated temperates is positioned below flange 44 and is clamped thereto by an outwardly extending shoulder or flange 48 formed at the base of stem member 30. The stem is held in position by a packing gland 50 and a packing nut 52. As shown in Fig. 1, tightening of packing nut 52 applies a compressive force to packing rings 38, 40, GB2163530A 5 42 to effect radial expansion into a fluid-tight seal about the stem.

Although it is possible to actuate the valve stem by many different types of actuators, including both manual, mechanical or auto matic, a handle member 54 has been shown.

This handle is releasably secured to stem member 30 by a nut 56 which clamps the handle to the top of packing nut 52. A co operating flat 58 is advantageously formed on the exterior of the stem for association with a flat (not shown) in the handle opening for pro perly positioning the handle on the stem.

However, the position of the handle and, in turn, the position of ball member C are limited 80 by depending stop members 62, 64, carried by handle 54- These stop members engage suitable surfaces on central body section 12 to provide fixed stops for the valve in the full open and full closed positions.

With continued reference to Fig. 1, the ball seat arrangement includes a pair of seat ring assemblies B disposed on opposite sides of ball member C. As shown, the seat ring as semblies are clampingly retained in position on 90 opposite sides of the ball at opposite ends of the main body section passageway 20. The seat ring assemblies are located substantially equidistant from and on diametrically opposite sides of the axis of rotation of the ball mem- 95 ber and include central openings 66, 68.

While the seat ring assemblies could be main tained in position by many different or alterna tive arrangements, they are shown as being located by shoulders 70, 72 defined by end 100 faces 74, 76 of end fittings 14, 16 respec tively. The inward limit of movement of the seat ring assemblies is defined by a pair of shoulders or steps 78, 80 which are formed by the inner end walls of counterbores ex tending inwardly of valve body passageway 20.

Still further, a seal is provided between cen tral body section 12 and end fittings 14, 16 by means of sealing rings 82, 84 which are 110 received in second counterbores 86, 88 re spectively. Each sealing ring is disposed about the outer circumference or outer peripheral surface of a portion of the associated seat ring assembly B, The sealing rings 82, 84 are 115 preferably constructed of a deformable, resili ent, heat-resistant and thermally stable ma terial, such as an expended carbonaceous ma terial and wire mesh composite to avoid prob- lems of sublimation and charring that may occur such as when a conventional type thermoplastic 0ring seal is exposed to a fire or other elevated temperatures. In the preferred construction, Grafoil (Registered Trademark) has been advantageously employed as the deformable and heat-resistant material. However, it will be appreciated that other materials, such as asbestos or ceramic composites, could also be employed. As the valve main 16 expand and contract upon heating and cooling during and after a fire, sealing rings 82, 84 continue to provide a satisfactory seal between the central body section and the end fittings.

The structural details of ball valve A as described hereinabove are with reference to the preferred valve construction. It will be readily apparent to those skilled in the art, however, that modifications may readily be made thereto to accommodate particular operational needs and/or requirements. Such changes do not affect the scope of the present invention as will be described in detail hereinafter.

With references to Figs. 2 to 6 and 13, description will be made of the specific details of seat assemblies B comprising the preferred embodiment of the invention. Fig. 2 shows the downstream seat assembly disposed adjacent end fitting 14 prior to valve make-up. Fig. 3 shows a view of the seat assembly of Fig. 2 at valve make-up and with the valve in a closed position under the influence of elevated fluid system pressure. Figs. 4, 5 and 6 illustrate the seat assembly B at successive stages after the valve has been exposed to a fire. Fig. 4 shows a primary soft plastic seat ring which has begun to heat flow and extrude out through the valve port. Fig. 5 shows the valve after the ball has made contact with the secondary seat. Fig. 6 shows the valve after the primary soft plastic seat ring has been completely destroyed and extruded or evaporated out of the valve body. Fig. 13 shows the seat assembly B after partial destruction, such as where the valve is exposed to a fire or radiant heat on one side only. Lines 3-3, 4-4, 5-5 and 6-6 of Fig. 13 correspond to the cross-sectional views of the seat assembly B shown in Figs. 3, 4, 5, and 6, respectively.

With particular reference to Figs. 2 and 3, each seat assembly B preferably comprises three components, i.e., a reinforcing or support ring 100, a primary seat ring 102 comprising a soft plastic seat member, and a secondary seat ring 104 comprising a deformable, non heat-flowing seat member. Although only a portion of one seat assembly is shown in these Figures, it will be appreciated that the other seat assembly is identical thereto except where otherwise specifically noted. Reinforcing ring 100 has an annular configuration including a central opening and is constructed from a rigid material, such as steel or other suitable metal. A first circumferentially continuous surface or end face 106 of the ring 100 faces associated shoulder 70 of end fitting 14. A second continuous surface or end face 108 faces and abuts counterbore end wall or step 78 of main body section passageway 20 to positively establish a forwardmost or home position for the reinforcing ring 100. A third continuous surface 110 faces generally to body section 12 and opposed end fittings 14, 130 wards the ball member, but is dimensioned to 6 GB2163530A 6 be spaced therefrom in order to prevent any abutment or interference therewith and to inhi bit distortion and displacement of the associ ated primary seat ring 102 between the third surface 110 of the reinforcing ring and the ball member.The outer circumference or peripheral surface 112 of ring 100 is disposed close to the side wall of passageway 20. Outer surface 112 and second end face 108 may alterna tively include a flange or step configured and dimensioned to engage shoulder 78 to further extend portions of support ring 100 axially inward of passageway 20 where overall valve dimensions may so require. However, such an additional flange is absent from the embodi ment shown to obviate additional machining steps.

With continued reference to Figs. 2 and 3, primary seat ring 102 has a central opening 118 which is smaller in size than the central opening of the reinforcing ring 100. The pri mary seat ring 102 is adapted for flexure generally towards and away from the reinforc ing ring 100. Seat ring 102 is configures to exert a spring-like mechanical elasticity against 90 the ball member. A first surface 120 generally faces the associated shoulder 70 of end fitting 14. A second surface 122 of the seat ring 102 faces reinforcing ring 100 for bearing en gagement and support against the first end face 106 of the reinforcing ring. A third sur face or ball-engaging surface 124 of the seat ring 102 generally faces ball member C for fluid-sealing engagement therewith. A flange or lip 126 extends axially outwards of the first 100 surface 120 of the seat ring 102 at outer peripheral surface 128. Lip 126 is preferably continuous about the seat ring 102 and located so its radially inner surface generally corresponds to the outside diameter of secon- 105 dary seat ring 104. Flange or lip 126 is further bevelled at the radially outermost region thereof and is slightly rolled over the radially outer edges of the secondary seat ring 104 in the manner shown. While not necessary, this 110 arrangement advantageously maintains the primary seat and secondary seat rings together as a subassembly. Preferably, the seat ring 102 is constructed from a soft resilient plastic material, such as Teflon or polyethylene. It 1-15 should be readily appreciated, however, that a wide range of other types of material, such as acetal resins and the like or even soft metals and ceramic composites, could also be advan- tageously utilized. The particular material cho- 120 sen will, to some extent, be dependent upon the normal operating conditions to which the valve will be subjected.

Included in primary seat ring 102 is a weir ring 130. Preferably, this ring is received in an annular undercut or groove 132 of seat ring 102 isolated from the valve fluid flow passageway. However, it is within the scope of the invention that weir ring 130 could be completely encased in seat ring 102 or, alter- natively, completely without the seat ring such as, for example, an axially directed lip of the secondary seat ring 104 extending towards the ball member at the inner diameter of the primary seat ring 102. Preferably, though, weir ring 130 is generally disposed radially intermediate of seat ring 102 between the associated secondary seat ring 104 and ball member C. In this preferred location, the weir ring 130 is isolated from exposure to the same hazards of wear and damage that affect the soft primary seat ring 102 in normal service. The weir ring is constructed of a thermally stable, non heatflowing material, preferably a Grafoil and wire mesh composite, similar to sealing rings 82, 84; however, mere Grafoil itself, wire mesh, a ceramic or even metal may be suitably employed.

Secondary seat ring 104 comprises a subas- sembly including a central frusto-conical disc spring 134 sandwiched between a first annular facing sheet 136 facing associated shoulder 70 and a second annular facing sheet 138 facing primary seat ring 102. The facing sheets 136, 138 are preferably constructed of Grafoil and are generally radially coextensive with disc spring 134; however, it is within the scope of the invention that the facing sheets 136, 138 may extend only over a portion of the disc spring as, for example, where the first facing sheet 136 may extend only over a portion of the disc spring 134 near the outer diameter of the disc spring, and the second facing sheet 138 may extend over the portion near the inner diameter of the spring 134. The latter embodiment may be particularly economical and advantageous in large size ball valves.

It has further been found to be advantageous for the face 74 of the support shoulder 70 to be knurled or grooved for better gripping of the facing sheet 136. Upon exposure of the valve to a fire, such improved grippifig inhibits slipping, flowing or extrusion of the facing sheet and the disc spring. It is possible at high temperatures for Grafoil to become somewhat flowable. The knurled or grooved face inhibits such action and facilitates the fluid tight seal.

The diameter at the outer end of the secondary seat ring 104 is such that the ring may be received within the cylindrical cavity defined by the inner wall of the axial flange 126 of the seat ring 102 and the first surface 120 thereof. The inner diameter of the secondary seat ring 104 is slightly larger than the diameter of the central opening 118 of the seat ring 102 to substantially isolate the secondary seat member from normal service contact with the ball member and system and associated wear and damage hazards.

Disc spring 134 is selected so that its force is sufficient under partial deflection to continuously urge the seat ring 102 towards the ball member. The spring must also allow deflec- 7 GB2163530A 7 tion thereof towards a flattened condition to accommodate ball shifting and engagement with the third surface 124 of the seat ring 102 during normal operating conditions. With particular reference to Fig. 3, it may be seen that a fluid-tight seal is effected by close containment of the primary seat ring 102 between the ball member C, the support ring 100, the valve main body 12, and the end fitting shoulder 70. During normal operating conditions, secondary seat ring 104 primary operates to bias and contain the primary seat ring 102 without performing a secondary seal ing function.

With reference to Figs. 1, 2 and 3, at the time of valve make-up, each of the seat as semblies B is moved such that each primary seat ring 102 is slightly rotatably flexed away from the other generally about its outer peri phery and against secondary seat ring 104 in 85 response to engagement between the ball-en gaging surface 124 and ball member C. This action slightly compresses the associated disc spring 134 towards a flattened condition. In addition to positioning the ball member, this spring deflection assures a seal force between the two seat rings and the ball member at ball- engaging surface 124 regardless of how low the system pressure may be. The secon30 dary vent orifice or opening 17 in the ball member C faces the inlet when the valve is in a closed position and assures that the inlet side seat ring assembly does not seal. Any fluid in the centre of the valve is free to ex35 pand upon heating or vapourizing, and relieve 100 through the vent orifice 17 without increasing the pressure in the valve.

Operation With particular reference to Figs. 4, 5, 6, 12 and 13, the operation of the above-described preferred embodiment upon destruction of the primary seat by fire will be specifically discussed.

Fig. 4 shows the soft plastic seat ring 102 being heated to a more fluid state and, in turn, flowing or being extruded through the central opening 66 of the secondary seat ring 104 by fluid pressure forces in the valve.

Upon softening of the seat ring 102, the disc spring 134 of the secondary seat ring 104 deflects to maintain a fluid-tight seal against ball member C and against end face 74 of shoulder 70.

With particular reference to Fig. 5, ball 120 member C has shifted axially downstream in valve A to compress the secondary seat ring 104 and to abut the weir ring 130. The sec ond facing sheet 138 which is sandwiched between disc spring 134 and seat ring 102 contacts ball member C at its radially inner most portion to effect a fluid-tight seal. Since the second facing sheet 138 is preferably con structed of a heat-resistant, deformable ma- terial, such as Grafoil, the sheet will conform to the engaging surface of the ball member C and thereby avoid the problems of prior firesafe ball valve designs which incorporate metal-to- metal type secondary seals. Similarly, first facing sheet 136 of the secondary seat ring 104 engages support shoulder 70 at shoulder end wall 74 at its radially outermost portion to effect a fluid-tight seal. The deformable property of the sheet 136 enables it to conform to the irregularities of surface 74 and the outermost radial edge of disc spring 134.

It is within the scope of the invention for the secondary seat member 104 to be without a first or a second facing sheet 136, 138 because it has been found that the disc spring 134, due to its circumferential elasticity, will form an appreciable metal-to-metal seal with ball member C, thereby overcoming the problems resulting from the ball member not being perfectly spherical nor match-iapped with the secondary seat ring.

The disc spring 134 of the secondary seat ring possesses a circumferential elasticity as well as an axial elasticity and, upon softening of the seat ring 102, the secondary seat ring deflects to maintain a fluid-tight seal between the ball member C and the end face 74 of shoulder 70. By circumferential elasticity is meant the capability of the secondary seat ring to deflect axially in one segment more so than in another segment.

Since the ball member C is not perfectly spherical and central opening 66 of disc spring 134 is not perfectly round, the ball and spring will contact only at a few high spots. The circumferential elasticity of disc spring 134 enables it to deflect at those high spots such that the ball makes substantially continuous contact against the innermost radial edge of disc spring 134. Similarly, the outermost radial edge of disc spring 134 contacts end face 74 only at a few high spots. The circumferential elasticity of disc spring 134 again enables it to deflect by various amounts around its perimeter and thereby establish a substantially continuous line of contact between the outermost radial edge of disc spring 134 and end face 74 of shoulder 70. Thus, the circumferential elasticity of the disc spring 134 com- pensates for imperfections in roundness at the inner and outer radial edges of disc spring 134, imperfections in sphericity of bail member C, and deviations from flatness of end face 74 of shoulder 70.

The weir ring 130 acts as a---weir-or dam to prevent excessive extrusion of the softening plastic seat ring 102 between the ball member C and the secondary seat ring 104 into the valve port. As a practical matter, a fire cannot always be expected to heat the surface of a fire-safe valve uniformly, particularly where the fire is a radiative fire near the valve and heats the closer side of the valve, but not the opposite side. Thus, in the course of a fire, it is reasonably foreseeable that the 8_ GB2163530A 8 plastic seat ring 102 will likely soften in 'only a first portion on its circular perimeter prior to softening in other areas. Without the weir ring 130, the first portion may excessively extrude into the valve port under system pressure, al- 70 lowing the ball member C to displace radially or sideways perpendicular to the valve port access. Consequently, as the ball member C moves downstream through softening plastic to meet the secondary seat ring 104, the ball 75 member may shift too far to one side and may contact the secondary seat ring 104 une venly, leaving large gaps and leakage paths were melting plastic and system fluids can blow through. It has been observed that such 80 leakage paths and gaps occur at positions generally spaced ninety degrees from the vec tor of direction of radial shift. The point one hundred eighty degrees from the vector of ra dial shift maintains a fluid seal by contact with 85 the remainder of the primary plastic seat ring 102. The rush of system fluids may then quench the plastic seat ring 102 preventing further melting. A gross leak thus developed can remain a gross leak no matter how much 90 extra fire is applied to the fire-safe valve.

An additional mechanism of partial seat de struction is illustrated in Fig. 12. A seat as sembly which does not include a weir ring is shown which has been exposed to a fire that 95 has caused only a portion 141 to extrude into the valve port. A large leakage path 143 has resulted due to the inability of the ball mem ber to contact the secondary seat ring 104.

The ball member C is checked against any radial or axial shift into the extruded portion by the substantially remaining portion of the primary plastic seat ring 102. The quenching action of the rushing leakage fluid quenches the primary plastic seat ring against further destruction or extrusion in spite of varying fire intensity.

However, with reference to Fig. 5, weir ring constrains the flow of soft and melting plastic no matter where on the seat ring peri meter plastic softening first occurs. Weir ring is positioned in seat ring 102 such that only a narrow annulus portion 144 may ex trude into -the valve port. The substantial por- tion 146 of seat ring 102 is blocked from extruded flow by the weir ring 130. The relatively small portion 144 which may extrude is of little substance and upon its extrusion, the associated displacement area into which the ball member C may then shift is insufficient to allow formation of a leakage path. It is also preferable that weir ring 130 be placed in seat ring 102 such that ball member C contacts the weir ring 130 simultaneously with contact of the secondary seat ring 104. Weir ring 130, thus, can further contribute to effecting a secondary seal upon destruction of the primary seat ring 102.

With reference to Fig. 6, the primary seat that the substantial portion 146 (Fig. 5) of the soft plastic seat ring has been sublimated or evaporated out through the valve port. A fluidtight seal remains between ball member C and secondary seat ring 104 as the ball member remains in contact with the radially innermost portion of the second facing sheet 138 which deforms in accordance with the ball member surface. The first facing sheet 136 similarly engages shoulder end wall 74 to maintain the fluid seal between the secondary seat ring 104 and the shoulder 70. In addition, it is advantageous that weir ring 130 be sized to engage the ball member upon destruction of the primary seat ring and associated downstream shifting of the ball. Such engagement facilitates a further fluid seal.

With particular attention to Fig. 13, along lines 6-6 it may be seen that the ball member has contacted the weir ring 130 after destruction of the primary seat ring and has also contacted the secondary seat ring to maintain a fluid seal (Fig. 6). Along lines 5-5, the extrusion of the substantial portion of the primary seat ring is blocked by weir ring 130 to prevent the formation of the leakage path in Fig. 12.

With particular reference to Fig. 8, an alternative embodiment of the present invention is shown. For ease of illustration and appreciation of this alternative, like components are identified by like numerals with a primed (') suffix and new components are identified by new numerals. Secondary seat ring 104' com- prises a unitary disc member 150 of heatresistant, deformable material, such as Grafoil or a Grafoil and wire mesh composite. Upon fire damage to the primary seat ring 102% ball member C' may shift axially downstream in response to fluid pressure to engage the radially innermost end portion of secondary seat ring 104' to effect a fluid-tight seal. Further, wall 74' which is preferably knurled, engages end fade 152 of the secondary seat ring to effect a fluid-tight seal between the secondary seat ring and support shoulder 70'. Secondary seat ring 104' may thereby conform to the engaging surface of the ball member C' and the wall 74'.

Yet another alternative embodiment of the invention is illustrated in Fig. 9 where like components are identified by like numerals with a double primed (") suffix. Secondary seat ring 104" comprises a disc spring 134" and a facing sheet 156 of heat-resistant, deformable material, such as Grafoil or Grafoil and wire mesh composite. Upon destruction of the primary seat ring 102" in a fire, the ball member in a closed position advances un- der system pressure against the secondary seat ring 104" and contorts the facing sheet 156 at its radially innermost portion to make a fluid-tight seal. Furthermore, as the fire pro gresses, disc spring 134" anneals. The sof ring 102 has been completely destroyed such 130 tening disc spring, contorted by the ball mem- 9 GB2163530A 9 ber under pressure, thereby conforms more readily to the surface 74" of support shoulder 7W and makes an improved metal-to-metal seal behind the spring. Yet another embodi ment of the invention similar to this embodi ment would comprise use of a single facing sheet on the disc spring surface facing the support shoulder. Such a construction would involve a metal-to-metal secondary seal to the ball and a facing sheet to shoulder seal. It is preferable to employ a knurled shoulder to contact the facing sheet.

Fig. 10 shows another alternative embodi ment of the present invention where like com ponents are identified by like numerals with a 80 triple primed (..) suffix. This embodiment of the invention includes a seat assembly comprising support ring 100-, a primary seat ring 102-, a secondary seat ring 104---including a disc spring 134-, a first facing sheet 136--and a second facing sheet 138- --. The facing sheets 136-, -138.. are constructed of Grafoil or other heat-resistant, deformable material. A weir ring is not included. Upon destruction of seat ring 102---in a fire, the ball member will 90 shift axially downstream and make a fluid seal at the second facing sheet 138---. The first facing sheet 136... engages knurled end wall 74... of support shoulder 70. .. to maintain the seal.

Finally, Fig. 11 relates to still another alternative embodiment of the present invention wherein like components are again identified by like numerals with a primed suffix. Secon- dary seat member 104.... may comprise a single disc spring, a single non heat-flowing deformable disc constructed of material such as Grafoil or a metal wire Grafoil mesh composite, or a combination of a disc spring and a Grafoil facing sheet similar to the secondary seat member 104" illustrated in Fig. 9. A weir ring 130 preferably constructed of a Grafoil and wire mesh composite, is included in the primary seat ring 102.... to contact the ball member upon partial or total destruction of the primary seat ring, and to block extrusion of the substantial portion 146.... of the seat ring 102... ..

Other modifications not specifically shown in the drawings may be readily incorporated into 115 seat ring assemblies B without in any way departing from the scope of the invention. It may, for example, be desirable to slightly modify the relative dimensional characteristics between the primary seat rings, the reinforcing rings and the secondary seat rings to accommodate particular operational requirements.

The invention has been described with reference to a preferred and several alternative em- bodiments. Obviously, modifications and alterations will occur to others upon a reading and understanding of this specification. All such modifications and alterations are intended to be within the scope of the appended claims.

Claims (15)

1. A ball valve including a valve body having a generally cylindrical passageway; a ball member disposed in said passageway and mounted for selective rotation between valveopen and valve-closed positions with said ball member being shiftable generally axially in said passageway under fluid pressure conditions at least when said valve is in said closed position; a pair of annular seat rings disposed in said passageway on opposite sides of said ball member between said ball member and a pair of shoulders in the valve body; and a weir ring co-operatively associated with at least one of said pair of seat rings for inhibiting extrusion of said seat ring upon exposure of said valve to elevated temperatures.

2. A ball valve as claimed in claim 1, wherein said weir ring is generally disposed radially intermediate said seat ring.

3. A ball valve as claimed in claim 2, wherein said weir ring is received in an annu lar groove in said seat ring. -

4. A ball valve as claimed in claim 3, wherein said annular groove is disposed in said seat ring in isolation from said fluid flow passageway for preventing exposure of said weir ring to normal operational wear hazards of the valve.

5. A ball valve as claimed in claim 2, 3 or 4, wherein said weir ring is encased in said seat ring.

6. A ball valve as claimed in any of claims 1 to 5, wherein a pair of annular disc springs is interposed between each seat ring and the respective shoulder for continuously urging said seat rings towards sealing engagement with said ball member, and wherein the annular disc spring associated with said seat ring includes annuir face sheeting of heat-resistant material.

7. A ball valve as claimed in claim 6, wherein said weir ring is generally interposed between said seat ring and the respective disc spring.

8. A ball valve as claimed in claim 6 or 7, wherein said heat-resistant material comprises expanded carbonaceous material.

9. A ball valve as claimed in claim 6, 7 or 8, wherein said annular face sheeting is disposed at each of the opposed faces of said disc spring and comprises a first facing sheet extending over a portion of a first face of said disc spring near an outer diameter of said spring facing the respective shoulder, and a second facing sheet extending over a portion of a second face of said disc spring near an inner diameter of said spring facing said ball member.

10. A ball valve as claimed in claim 1, wherein a pair of annular disc springs is inter posed between each seat ring and the respec tive shoulder for continuously urging the seat rings towards sealing engagement with the ball member, and wherein said weir ring corn- GB2163530A 10 prises an axially directed lip of one of said annular disc springs and extends towards said ball member at the inner diameter of the respective annular seat ring.

11. A ball valve as claimed in any of - claims 1 to 10, wherein said weir ring is sized to contact said ball member upon destruction of the respective seat ring.

12. A ball valve as claimed in claim 11, wherein said weir ring is further sized to contact the respective shoulder upon destruction of said seat ring by elevated temperatures to form a fluid seal between said ball member and the respective shoulder.

13. A ball valve including a body having a central passageway, a ball member having a fluid flow opening therethrough and being positioned in said passageway and mounted for selective rotation between valve-open and valve-closed positions to control fluid flow through said valve, a flexible seat ring supported in said passageway for fluid sealing engagement with said ball member; and a deformable, heat-resistant secondary seat mem- ber encased within said primary seat ring for isolation of said secondary seat member from normal service contact with the ball member and system fluid whereby, upon damage to said flexible seat ring by exposure to elevated temperatures, said secondary seat member engages said ball member to seal said valve.

14. A ball valve as claimed in claim 13, wherein said secondary seat member is disposed in a radially intermediate position of said flexible seat ring and is sized to inhibit extrusion of said flexible seat ring through said central passageway upon exposure of said valve to elevated temperatures.

15. A ball valve constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.

Printed in the United Kingdom for Her Majesty's Stationery Office, Dd 8818935, 1986, 4235. Published at The Patent Office, 25 Southampton Buildings. London, WC2A 1 AY. from which copies may be obtained.