GB2129101A

GB2129101A - Ball valve

Info

Publication number: GB2129101A
Application number: GB08327356A
Authority: GB
Inventors: Peter Charles Williams; Ulrich Hubert Koch; Timothy James Francis
Original assignee: Whitey Co
Current assignee: Whitey Co
Priority date: 1982-10-14
Filing date: 1983-10-13
Publication date: 1984-05-10
Also published as: GR78950B; FR2534658A1; SE8305619D0; NO833724L; NL8303515A; DE3336099A1; ZA837253B; GB2129101B; CA1242426A; NZ205783A; IT8349154A0; SE8305619L; DK472983D0; JPS5989871A; DE3336099C2; FR2534658B1; IE832416L; JPH0549867B2; LU85044A1; AU565423B2

Abstract

A soft-seated fire-safe ball valve includes a pair of seat assemblies each comprising a rigid reinforcing ring (100), an elastic seat ring (102), and a deformable, heat-resistant secondary seat ring (104) interposed between the elastic seat ring and a shoulder (70). Upon fire damage to the elastic seat ring (102), the secondary seat ring (104) engages the ball member (c) to seal the valve (Fig. 6). Also, a weir ring (130) may be received in the seat ring (102). The weir ring (130) inhibits extrusion of a substantial portion 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. <IMAGE>

Description

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

When employed in the valve art, the term "firesafe" has come to mean a valve that satisfies certain specified conditions when subjected to a fire; see Arant, Fire-Safe Valves-An Overview, Proceedings, Thirty-Sixth Annual Symposium on Instrumentation for the Process Industries (Texas A & University, 1981). Unfortunately, different sets of conditions have been promulgated by different organizations and the valve industry has not yet recognized a uniform standard. Basically, according-to one of the standards (American Petroleum Institute 607), if a valve will substantially maintain a fluid seal in a closed position at a valve body temperature of at least 5930C (11 00 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 adjacent 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 valveclosed position. Such shifting causes the ball member to act against and to flex and deform the downstream seat ring to enhance its sealing engagement 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 begins 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 destruction of the plastic seat allows the ball member to shift further under fluid pressure conditions until the bail 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 engagement against the ball member and allows substantially 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 prevent 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 exceed 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 contaminants that may become lodged between the ball member and the ball sealing surface and thereby provide additional leakage paths.

One overali 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 obtaining 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 limited economic and practical value.

A common type of fire-resistant ball valve design includes a primary soft seat of a plastic 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 comprises a metal rim or washer interposed between the soft plastic primary seat and a valve body support shoulder.

This design suffers 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 contact with the metal seat. For a metal-to-metal seal to be anywhere near leak-tight in a fire-safe or other application, the sealing surface must be match lapped or burnished, one into the other. Since such a procedure is very expensive, match lapping is an economically impractical 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 advantages of match fitting would have been lost. Ball valve designs incorporating the secondary metal seat or high temperature composite seat also suffer from the problems of partial deterioration and quenching of the primary seat and the problems of loose and blocking 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-resistant material which is more deformable and resilient than metal. Typically, carbon or graphite rings have been used. While such designs 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 secondary 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 secondary seat is damaged.Such a multiplicity of seats increases the size, complexity, and cost of the valve without adding a reliable emergency 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 in 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 firesafe ball valve and seat assembly which would operate satisfactorily at normal operating conditions and also seal the valve in a valveclosed 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 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 valveclosed 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 supported 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 secondary 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 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 sealing engagements.

Still another object of the invention is the provision of a ball valve which will maintain fluid sealing upon partial or complete destruction 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 contaminants between the ball member and ball-engaging and sealing surfaces.

Another object is the provision of a secondary seat which will function upon fire damage to the ball valve regardless of the design and construction material of the primary seat.

Still another object is the provision of a secondary 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 secondary seat that is removed from the deterioration and wear forces of fluid flow associated with normal service.

More specifically, the invention includes a firesafe ball valve comprising 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 valveclosed 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 bail member and a pair of radially inward-extending counterbores also being provided in said passageway disposed on opposite sides of said ball member; and a pair of composite seat assemblies 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 reinforcing ring having a central opening and abutting an inner end wall of the respective counterbore, a seat ring abutting said reinforcing ring and designed for elastic flexure generally towards and away from said reinforcing ring, said seat ring having a central opening and ball-engaging surface facing said ball member for sealing engagement with said bail member, and a secondary seat ring interposed between said flexible seat ring and the respective shoulder, said secondary seat ring including 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 frusto-conical configuration in an unstressed condition. The sheet of expanded carbonaceous material is generally radially 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 shoulder 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 the 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 Figure 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 Figure 1, but with the valve in a closed position under the influence of elevated fluid system pressures; Figure 4 is a sectional view, similar to Figure 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 Figure 4, where the ball has made contact with the secondary seat; Figure 6 is a sectional view, similar to Figures 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 Figure 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 incorporates another alternative embodiment of the invention; Figure 11 is an enlarged sectional view of still another alternative seat assembly embodiment which incorporates the invention;; Figure 12 is an enlarged perspective view of the seat assembly of Figure 10 after partial destruction upon exposure to a fire and having been removed from the valve body for ease of illustration; and Figure 1 3 is an enlarged perspective view of the seat assembly of Figure 1 after partial destruction 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, Figure 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 Figures 1 and 7, ball valve A includes a body or housing 10 having a main or central body section 12 and opposed end fittings 14, 16. Seat assemblies B and ball C are mounted within the main body section 12 and the ball member is arranged for selective rotation by a stem and actuating handle assembly 18. Ball member C includes a first or principal fluid flow opening 1 5 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 1 5 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.

Substantially all of the details of the portions of the valve illustrated in Figure 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 axially-extending fluid flow opening 20 which is only slightly larger in diameter than ball member C. Each of the end fittings 14, 1 6 is releasably connected to central body section 1 2 by a plurality of longitudinally extending tie bolts 22 received through boit bores 24 of opposed end fittings 14, 1 6 and fittedly received in main body section 12 (Figure 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 sprinkier.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, 1 6 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 member 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 temperatures 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 Figure 1, tightening of packing nut 52 applies a compressive force to packing rings 38, 40, 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 automatic, 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 properly positioning the handle on the stem. However, the position of the handle and, in turn, the position of ball member C are limited by depending stop members 62, 64, carried by handle 54. These stop members engage suitable surfaces on central body section 1 2 to provide fixed stops for the valve in the full open and full closed positions.

With continued reference to Figure 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 assemblies are clampingly retained in position on 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 member and include central openings 66, 68. While the seat ring assemblies could be maintained in position by many different or alternative arrangements, they are shown as being located by shoulders 70, 72 defined by end faces 74, 76 of end fittings 14, 1 6 respectively.

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 extending inwardly of valve body passageway 20.

Still further, a seal is provided between central body section 12 and end fittings 14, 1 6 by means of sealing rings 82, 84 which are received in second counterbores 86, 88 respectively. 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 preferably constructed of a deformable, resilient, heatresistant and thermally stable material, such as an expended carbonaceous material and wire mesh composite to avoid problems of sublimation and charring that may occur such as when a conventional type thermoplastic O-ring 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 body section 1 2 and opposed end fittings 1 4, 1 6 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 I 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 Figures 2 to 6 and 13, description will be made of the specific details of seat assemblies B comprising the preferred embodiment of the invention. Figure 2 shows the downstream seat assembly disposed adjacent end fitting 14 prior to valve make-up. Figure 3 shows a view of the seat assembly of Figure 2 at valve make-up and with the valve in a closed position under the influence of elevated fluid system pressure. Figures 4,5 and 6 illustrate the seat assembly B at successive stages after the valve has been exposed to a fire. Figure 4 shows a primary soft plastic seat ring which has begun to heat flow and extrude out through the valve port.

Figure 5 shows the valve after the ball has made contact with the secondary seat. Figure 6 shows the valve after the primary soft plastic seat ring has been completely destroyed and extruded or evaporated out of the valve body. Figure 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 Figure 13 correspond to the cross-sectional views of the seat assembly B shown in Figures 3, 4, 5, and 6, respectively.

With particular reference to Figures 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 1 00. A third continuous surface 110 faces generally towards the ball member, but is dimensioned to be spaced therefrom in order to prevent any abutment or interference therewith and to inhibit distortion and displacement of the associated 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 alternatively 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 embodiment shown to obviate additional machining steps.

With continued reference to Figures 2 and 3, primary seat ring 102 has a central opening 11 8 which is smaller in size than the central opening of the reinforcing ring 100. The primary seat ring 102 is adapted for flexure generally towards and away from the reinforcing ring 100. Seat ring 102 is configured to exert a spring-like mechanical elasticity against the ball member. A first surface 1 20 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 engagement and support against the first end face 106 of the reinforcing ring. A third surface or ballengaging 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 surface 1 20 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 secondary seat ring 1 04. Flange or lip 1 26 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 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 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 advantageously utilized. The particular material chosen 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 1 30. Preferably, this ring is received in an annular undercut or groove 1 32 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, alternatively, 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 1 30 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 1 30 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 heat-flowing 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 subassembly including a central frusto-conical disc spring 134 sandwiched between a first annular facing sheet 1 36 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 1 36, 1 38 may extend only over a portion of the disc spring as, for example, where the first facing sheet 1 36 may extend only over a portion of the disc spring 1 34 near the outer diameter of the disc spring, and the second facing sheet 1 38 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 1 36. Upon exposure of the valve to a fire, such improved gripping inhibits slipping, flowing or extrusion of the facing sheet and the disc spring. It is possible at high temperatures for Grafoil to become somewhatflowable. 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 1 04 is slightly larger than the diameter of the central opening 11 8 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 1 34 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 deflection 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 Figure 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 primarily operates to bias and contain the primary seat ring 102 without performing a secondary sealing function.

With reference to Figures 1, 2 and 3, at the time of valve make-up, each of the seat assemblies B is moved such that each primary seat ring 102 is slightly rotatably flexed away from the other generally about its outer periphery and against secondary seat ring 104 in response to engagement between the ball-engaging surface 124 and ball member C. This action slightly compresses the associated disc spring 1 34 towards a flattened condtion. 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 secondary 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 expand upon heating or vapourizing, and relieve through the vent orifice 1 7 without increasing the pressure in the valve.

Operation With particular reference to Figures 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.

Figure 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 Figure 5, ball member C has shifted axially downstream in valve A to compress the secondary seat ring 104 and to abut the weir ring 1 30. The second facing sheet 138 which is sandwiched between disc spring 1 34 and seat ring 102 contacts ball member C at its radially innermost portion to effect a fluid-tight seal. Since the second facing sheet 1 38 is preferably constructed of a heatresistant, deformable material, such as Grafoil, the sheet will conform to the engaging surface of the ball member C and thereby avoid the problems of prior fire-safe 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 1 34.

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 matchlapped 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 1 34 enables it to deflect at those high spots such that the ball makes substantially continuous contact against the innermost radial edge of disc spring 1 34. 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 1 34 compensates for imperfections in roundness at the inner and outer radial edges of disc spring 134, imperfections in sphericity of ball 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 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, allowing 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 member may shift too far to one side and may contact the secondary seat ring 104 unevenly, leaving large gaps and leakage paths where melting plastic and system fluids can blow through. It has been observed that such leakage paths and gaps occur at positions generally spaced ninety degrees from the vector of direction of radial shift. The point one hundred eighty degrees from the vector of radial shift maintains a fluid seal by contact with 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 extra fire is applied to the fire-safe valve.

An additional mechanism of partial seat destruction is illustrated in Figure 1 2. A seat assembly which does not include a weir ring is shown which has been exposed to a fire that has caused only a portion 141 to extrude into the valve port. A large leakage path 1 43 has resulted due to the inability of the ball member 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 Figure 5, weir ring 130 constrains the flow of soft and melting plastic no matter where on the seat ring perimeter plastic softening first occurs. Weir ring 1 30 is positioned in seat ring 102 such that only a narrow annulus portion 144 may extrude into the valve port. The substantial portion 146 of seat ring 102 is blccked 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 1 30 be placed in seat ring 102 such that ball member C contacts the weir ring 130 simultaneously with contact of the secondary seat ring 1 04. Weir ring 130, thus, can further contribute to effecting a secondary seal upon destruction of the primary seat ring 102.

With reference to Figure 6, the primary seat ring 102 has been completely destroyed such that the substantial portion 146 (Figure 5) of the soft plastic seat ring has been sublimated or evaporated out through the valve port. A fluid-tight 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 Figure 13, along linus 6-6 it may be seen that the ball member has contacted the weir ring 1 30 after destruction of the primary seat ring and has also contacted the secondary seat ring to maintain a fluid seal (Figure 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 Figure 12.

With particular reference to Figure 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' comprises a unitary disc member 1 50 of heat-resistant, 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 face 1 52 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 wail 74'.

Yet another alternative embodiment of the invention is illustrated in Figure 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 1 56 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 under system pressure against the secondary seat ring 104" and contorts the facing sheet 1 56 at its radially innermost portion to make a fluid-tight seal. Furthermore, as the fire progresses, disc spring 134" anneals.The softening disc spring, contorted by the ball member under pressure, thereby conforms more readily to the surface 74" of support shoulder 70" and makes an improved metal-to-metal seal behind the spring. Yet another embodiment of the invention similar to this embodiment 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.

Figure 10 shows another alternative embodiment of the present invention where like components are identified by like numerals with a 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 heatresistant, deformable material. A weir ring is not included. Upon destruction of seat ring 102"' in a fire, the ball member will 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, Figure 11 relates to still another alternative embodiment of the present invention wherein like components are again identified by like numerals with a primed suffix. Secondary seat member 104off" may comprise a single disc spring, a single non heat-flowing deformable disc constructed of material such as Grafoil or a metal wire and Grafoil mesh composite, or a combination of a disc spring and a Grafoil facing sheet similar to the secondary seat member 104" illustrated in Figure 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 1 02"".

Other modifications not specifically shown in the drawings may be readily incorporated into 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 severai alternative embodiments. Obvously, 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

1. 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 valveclosed positions to control fluid flow through said valve, a pair of radially inward extending shdulders 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 supported 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 secondary seat ring element engages said ball member to seal said valve.

2. A ball valves claimed in claim 1, wherein said secondary seat ring element is constructed of expanded carbonaceous material.

3. A ball valve as claimed in claim 1 or 2, wherein said seat assembly further includes a disc spring interposed between said secondary seat ring element and the respective shoulder for urging said elastic seat ring and said secondary seat ring element towards engagement with said ball member.

4. A ball valve as claimed in claim 3, wherein said disc spring and said secondary seat ring element are generally radially coextensive with each other.

5. A fire-safe ball valve comprising 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 valveopen 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 counterbores also being provided in said passageway disposed on opposite sides of said ball member; and a pair of composite seat assemblies 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 reinforcing ring having a central opening and abutting an inner end wall of the respective counterbore, a seat ring abutting said reinforcing ring and designed for elastic flexure generally 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 respective shoulder, said secondary seat ring including a disc spring having a central opening and a generally frustoconical 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.

6. A ball valve as claimed in claim 5, wherein said ball member and said pair of seat assemblies are sized so that, whenassembled, said flexible seat ring and said secondary seat ring of each assembly are flexed and stressed to urge said flexible seat ring towards contact with said ball member.

7. A ball valve as claimed in claim 5 or 6, wherein first and second annular sheets are disposed at the opposite faces of said disc spring.

8. A ball valve as claimed in claim 7, wherein the annular sheets are radially coextensive with said disc spring.

9. A ball valve as claimed in claim 7 or 8, wherein one sheet of expanded carbonaceous material is disposed contiguous to the respective shoulder, and the other sheet is disposed contiguous to said flexible seat ring.

10. A ball valve as claimed in claim 9, wherein, upon damage to a seat ring due to exposure to elevated temperatures, said other sheet contacts said ball member for sealing engagement therewith.

11. A ball valve as claimed in claim 9 or 10, wherein said one sheet contacts the respective shoulder for fluid sealing engagement therewith,

12. A ball valve as claimed in any preceding claim, wherein said annular sheet of expanded carbonaceous material is positioned in at least one of said seat assemblies in substantial isolation from said central opening of the associated flexible seat ring for preventing exposure of said sheet to normal operational wear hazards of the valve.

13. A ball valve as claimed in claim 12, wherein said annular sheet of expanded carbonaceous material is interposed between said flexible seat ring and said disc spring.

14. A ball valve as claimed in claim 12, wherein said annular sheet of expanded carbonaceous material is interposed between said disc spring and the respective shoulder.

15. A ball valve as claimed in any preceding claim, wherein said radially inward extending shoulders include knurled surfaces for engagement with said secondary seat ring or element.

1 6. A ball valve as claimed in any preceding claim, wherein said shoulders are on body fittings secured to a main section of said body by means of a plurality of fastener members received by said main body section.

17. A ball valve as claimed in any preceding claim, wherein said ball member further includes means for relieving pressure increases in said valve body due to fluid heating and vaporization upon exposure of said valve to elevated temperatures.

18. A ball valve as claimed in claim 17, wherein said relieving means comprises a vent orifice disposed normally to said fluid flow opening to face a fluid inlet opening of said valve upon closure of said valve.

19. A ball valve as claimed in any preceding claim, further including a weir ring in at least one of said pair of seat assemblies for inhibiting extrusion of said flexible seat ring upon exposure of said valve to elevated temperatures.

20. A ball valve as claimed in claim 19, wherein said weir ring is positioned in said one seat assembly in substantial isolation from said central opening of the associated flexible seat ring for preventing exposure of said weir ring to normal operational wear hazards of the valve.

21. A ball valve as claimed in claim 20, wherein said weir ring is encased in said flexible seat ring.

22. 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 valve-open and valveclosed 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.

23. A ball valve as claimed in claim 22, wherein said weir ring is generally disposed radially intermediate said seat ring.

24. A ball valve as claimed in claim 23, wherein said weir ring is received in an annular groove in said seat ring.

25. A ball valve as claimed in claim 24, 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.

26. A ball valve as claimed in claim 23, 24 or 25, wherein said weir ring is encased in said seat ring.

27. A ball valve as claimed in any of claims 22 to 26, 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 annular face sheeting of heat-resistant material.

28. A ball valve as claimed in claim 27, wherein said weir ring is generally interposed between said seat ring and the respective disc spring.

29. A ball valve as claimed in claim 27 or 28, wherein said heat-resistant material comprises expanded carbonaceous material.

30. A ball valve as claimed in claim 27, 28 or 29, 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 second face of said disc spring near an inner diameter of said spring facing said ball member.

31. A ball valve as claimed in claim 22, wherein a pair of annular disc springs is interposed between each seat ring and the respective shoulder for continuously urging the seat rings towards sealing engagement with the ball member, and wherein said weir ring comprises 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.

32. A ball valve as claimed in any of claims 22 to 31, wherein said weir ring is sized to contact said ball member upon destruction of the respective seat ring.

33. A ball valve as claimed in claim 32, 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.

34. A ball valve including a body having a central passageway, a bail 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 member 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.

35. A ball valve as claimed in claim 34, 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.

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