GB2096280A - Safety relief of valve cavity pressure in the event of fire - Google Patents

Abstract

The housing (12) of a valve is internally provided with a valve cavity- to-throughbore bypass conduit (62) on its upstream side. A relatively vulnerably-placed body (134) of heat- activated material normally forces a bypass valve (93) to close this conduit. In the event of a fire in the vicinity of the protected valve, the heat-activated body (134) loses its forcing capability and the bypass valve (93) opens, moving off a first metal- to-metal seat (78) and making a second metal-to-metal back seat (98). Any fluid that had previously leaked from the throughbore (14) of the protected valve into the valve cavity (23) may then pass to the upstream side of the protected valve, instead of becoming dangerously highly pressurized in the valve cavity. <IMAGE>

Description

SPECIFICATION Apparatus improvement for safely relieving valve cavity pressure in the event of a fire in the vicinity of the valve.

In a valve having a housing with throughbore and a valve cavity which intersects the throughbore, one or more valve seats are usually -provided at the intersection and a movable valve member is mounted in the cavity for sliding, rotating or revolving relation to the valve seat or seats. Usually the valve member is provided with a stem which passes out of the housing through a bearing and sealing arrangement. Outside the valve housing the stem customarily is provided with some form of actuator for rotating and/or longitudinally moving the stem to relatively open and close the valve by moving the valve member with respect to the valve seat or seats.Especially where the valve is a ball valve or a gate valve, the valve member may remain in contact with the valve seats as the valve is opened and closed and normally fluid being controlled by the valve does not flow through the region of the valve cavity that lies between the valve member and the valve stem bearing and sealing arrangement. However, in the course of normal use of a valve it is not uncommon for a certain amount of the fluid being controlled by the valve to flow into or leak into this region due to imperfections on or wear of the valve seats and the valve member surface, or lateral play allowed by the bearing and sealing arrangement, especially with changes in temperature and after a long period of time in service.Leakage into this valve cavity region may be more prevalent where the controlled fluid is volatile and subject to leakage into the area as a vapor, whereupon it condenses and collects there.

Sometimes there is no net accumulation of leaked fluid in this cavity region because what collects there under some conditions leaks back the same way it came underotherconditions.

In many cases the accumulation of some leaked, controlled fluid in the aforesaid cavity region is entirely tolerable and would hardly be given a second thought. It can represent a problem, however, in valves intended for use in controlling fuel or oxidizer fluids in a vicinity that could be subject to an unusually high temperature, e.g. due to a fire. Typical of such installations are petroleum wellheads, collection, separation, refining, storage, transportation and distribution and use facilities; petrochemical plants, power generating plants; and in the chemical processing industry, generally. In such cases, in the event of a fire or the like the heat may become so intense as to cause internal valve parts to become distorted and unworkable.But a further danger can be represented by any quantum of leaked, controlled fluid which theretofore had accumulated in the valve cavity between the valve member and the valve stem bearing and sealing arrangement. The further danger is that the pressure of this trapped fluid may rise so swiftly and so high that the valve housing is thereby blown apart in an explosion that leaves the conduit, vessel or well formerly controlled by the valve, open and able to freely feed fuel, oxidizer or the like to the fire. As a result a fire which initially was small and containable rapidly could become major.

The valve improvement of the present invention was made, having the above situation in mind, in order to provide a means for safely relieving valve cacity pressure in the event of a fire in the vicinity of the valve. According to the invention the valve housing is provided with an internal passageway that extends between the valve cavity, between the valve member and the valve stem bearing and sealing arrangement, and the valve housing throughbore on the upstream side of the upstream valve seat or intersection of the throughbore with the valve cavity. This internal passageway is normally closed by a relief valve which makes a metal-to-metal primary seal in the internal passageway.However, this valve is forced towards its normally closed position by a body of temperature activated, e.g., eutectic, material that, while enclosed, is positioned to be relatively vulnerable to exposure to high temperature should there be a fire or other unusuai high temperature event in the vicinity of the valve being protected.

In the event of fire or the like, the temperature activated material meits and runs out, or decreases in overall volume or changes shape or the like, sufficiently to lose its capacity to force the relief valve to remain closed. Accordingly, any increase in pressure within the valve cacity, e.g., due to heating of controlled fluid that theretofore has leaked into the cavity of the protected valve around the valve member of the protected valve, will force the relief valve to open. In opening, the relief valve will move off its usual metal-to-metal seat, and onto a second one.With the relief passageway thus open, pressure in the valve cacity will be relieved into the upstream side of the throughbore of the housing of the protected valve, and the second metal-to-metal sealing relationship established as the relief valve opens will protect against leakage should the stem packing of the relief valve also become damaged by heat, the effects of age, or the like.

The principles of the invention will be further discussed with reference to the accompanying drawings wherein a preferred embodiment is shown. The specifics illustrated in the drawings are intended to exemplify, rather than limit, aspects of the invention as defined in the claims.

In the drawings: FIGURE 1 is a perspective view of a valve that is being protected using the apparatus improvement of the present invention. In this view some portions of the valve housing are broken away and sectioned, to expose interior details.

FIGURE 2 is a larger scale, fragmentary longitudinal sectional view of the protected valve, showing the apparatus improvement in more detail as it would appear under normal conditions, with the bypass conduit being closed by the bypass valve that is, in turn, forced closed bv a body of heat-activated material.

FIGURE 3 is a view similar to FIGURE 2, but showing the appearance of the structure after a fire has activated the heat-activated material and permitted the bypass valve to open.

The invention is described herein in relation to a Graygate(D gate valve 10, a commercial product of Gray Tool Company, Houston, Texas 77001.

The valve 10 includes a housing 12 having a longitudinal bore 14. At each end of the bore 14, the housing is provided with an end flange 1 6 for permitting the valve to be sealingly connected between two conduits, or between a vessel and a conduit, or incorporated in a wellhead completion assembly, or the like.

The housing 12 further includes a central enlargement 18 providing a valve cavity 20 which transversally intersects the bore 1 4 intermediate the ends 16. The cavity 20 also intersects one side of the housing, this intersection being surrounded by a ring-shaped flange 21. A bonnet 22 is secured to this flange, e.g., by a circle of threaded studs 24 based in the flange 21 and having nuts 26 threaded thereon. As the bonnet 22 is somewhat dome-shaped, the valve cavity 20, in effect, continues up into the under side of the bonnet 22. At the intersection, the cavity wall is circumferentially sealed by an annular seal ring 28.

At the upstream (shown) and downstream (hidden) intersections of the valve cavity 20 with the valve housing throughbore 14, annular valve seats 30 are provided in respective corresponding circumferentially extending recesses 32.

The gate valve 10 further includes a gate assembly 34, which comprises a pair of gate plates 36, a non-rising, rotatable valve stem 38 and a connection device 40 (known per se) which threadably connects the gate plates to the valve stem, but allows the two gate plates to move toward and away from one another to a very limited degree. The mobility is desirable so that the gate plates 36 can be firmly, sealingly pressed away from one another and against the respective valve seats 30 when the valve is in a fully closed condition, but fairly immediately loosen away from the valve seats as the valve begins to be opened, to avoid undue wear and to decrease the force needed to open and close the valve except when it is almost fully closed.

The pressure to urge the gate plates away from one another when the valve is fully closed is provided by an expander 42 in the form of a pair of diametrically opposed, vertically depending legs 44 integrally joined at their upper ends to an oval ring 46. This ring 46 rests on a ledge 48 in the valve cavity 20. Each leg 44 near its lower end is provided with two laterally oppositely outwardly facing wedging surfaces 50 adapted to bear against corresponding inwardly facing wedging surfaces 52 on the respective gate plates.

Wedging contact is made only when the gate is almost fully closed, and continues for so long as the gate is fully closed. It subsides almost immediately as one begins to open the gate.

The valve stem 38 passes out of the housing 12 through a central bore 54 of the bonnet 22. An enlarged coaxially annular cavity 56 in the bore 54 is provided with a bearing and sealing arrangement 58 which journals the stem 38 for non-rising rotation and forms an annular seal between the valve stem and the bonnet bore.

The apparatus improvement provided in accordance with the principles of the invention is generally suggested at 60 in FIGURE 1. It is shown in more detail in FIGURES 2 and 3.

Referring first to Figure 2, the valve housing 12 is provided with an internal passageway 62 having an inlet port 64 at its intersection with the valve cavity 20 and an outlet port 66 at its intersection with the upstream segment of the bore 14.

For ease of manufacture, the passageway 62 may be formed, as shown, in two straight segments which intersect at generally right angles within the valve housing. One segment 68,the one which ends at the outlet port 66, has its original starting end (adjacent the ledge 48), permanently closed-off by a threaded plug 70. The other segment 72 between its starting end at 74 in the bonnet-mounting flange of the housing 12 and to just beyond the place of intersection of the two segments receives a bypass valve 76. To this purpose, this segment 72 is counterbored to a first level, ending just beyond the place of intersection of the first and second segments, to provide an annular valve seat 78 in the passageway 62. The segment 72 is also counterbored to a second level, ending about the same distance short of the place of intersection to provide an annular shoulder 80.The outer portion of the second counterbored region is shown being internally threaded at 82.

Received first in the well 84 provided by the second counterbore is a wedge ring 86 which has a flat bottom resting on the annular shoulder 80.

The ring 86 is nearly as great in outer diameter as the internal diameter of the well at the shoulder 80, but decreases in outer diameter from there to provide a wedge-shaped annulus.

The bypass valve 76 further includes a valve member 88. As shown, this is basically a cylindrical rod-shaped stem element 90 having a conically tapering inner end 92 and a coaxially annular enlargement 93 located in the well 84 near the shoulder 80. In the region between the valve seat 78 and the shoulder 80, the passageway 62 is shown being of slightly larger diameter than the rod portion 90 of the valve member 76.

Prior to being installed in the well 84, the valve member 76 is sub-assembled to a packing and sealing arrangement 95. This arrangement is shown including a multi-functional tubular body 94. The tubular body 94 has a coaxially annular constricting flange 96 in the bore thereof the axially inner annular face 98 of which constitutes a back seat, and the axially outer annular face 100 of which constitutes the bottom wall of a packing chamber which is shown receiving and being filled by a stack of rings of conventional packing material 102. The axially inner end of the body 94 is provided near its radially outer extent with a tapering axially extending tubular sealing flange 1 03. The exterior of the body 94 is circumferentially relieved radially outwardly of the packing chamber to provide an axially outwardly facing coaxially annular stop shoulder 1 06.

A tubular packing gland member 108 is provided. This member has a throughbore 110 sized to telescopically receive the rod 90 of the valve member. The bore 110 is counterbored at both ends to provide an inner well 112 and an outer well 114. The packing gland member 108 is externally threaded at 116. When it is threaded into the threaded region 82, its inner end 11 8 abuts the stop shoulder 106 and the inverted annular end wall 102 of the inner well 112 axially compresses, and thus radially expands and activates the packing 102 to circumferentially seal between the body 94 and stem 90 to the level of the axially outer end of the body 94.Further screwing-in of the packing gland 108, e.g., by wrenching its non-circular perimetrical wrenching surface 1 22 which still protrudes externally of the housing 12, forces the sealing flange 104 more deeply into the wedge shaped annulus radially between the wedge ring 86 and the well 84 sidewall, deflecting, deforming and/or compressing the metals of which these parts are made, into metal-to-metal circumferential sealing engagement at 124.

The axially outer well 114 of the packing flange member 108 is shown lying generally outside the housing 12 and is internally threaded at 126 to receive a cap 128. The cap 128 has a disk-shaped outer end wall 130 and an externally threaded skirt 132. Received within the cap 128, up against the end wall 130 as if it were a cap-liner wafer, plug or the like is a cylindrical body 134 of heatactivated material. The axial thickness of this body 1 34 is such that as the cap is tightened, the body 1 34 abuts between the cap end wall and the axially outer end 136 of the stem 90 of the bypass valve.Further tightening of the cap 128 thus forces the valve member axially inwards as far as it will go, i.e., so that the conically tapered axially inner end 92 forms a metal-to-metal seal against the valve seat 78, thus completely blocking the passageway 62 intermediate its ports 64 and 66.

This is the normal condition of the passageway 62. For a typical valve 10, its passageway 62 may remain closed by its bypass valve 76 for the whole working life of the valve 10.

It should now be noticed that the annular enlargement 93 is located centrally within a cavity provided by the central bore of the wedge ring 86 and the axially inner well of the tubular body 94.

Accordingly, the enlargement 93 has a generally axially outwardly facing annular end surface 138 which normally is axially spaced from the back seat surface 98 of the tubular body 94.

The body of heat-activated material 1 34 typically is a plug of so-called "eutectic" material, i.e., material which loses its structural integrity upon being heated to a preselected elevated temperature. Typically it may be composed of an alloy including lead, bismuth, antimony and/or tin.

Such bodies are in common use as melt-away actuators for the sprinkler systems of warehouses and public buildings. The body 134 may be a solid plug that will melt and run away, e.g., through the annular space 140 and into the cavity 142.

Alternately, the body could be made as a metal sponge, or as a star-shaped element so that as it softened or melted it could become axially thinner 'by filling voids originally provided in or around it somewhere between its axially opposite end faces In any event as the body 134, due to exposure to some unusual high temperature event occurring in the vicinity of the closed valve 10 softens or melts sufficiently to lose its structural integrity, it becomes no longer capable of acting as a shim means between the cap 128 and the axially outer end 136 of the stem 90. Then, as the presure on volatile controlled fluid begins to build-up in the valve capacity 20, due to heating, the safety feature goes into effect. Instead of continuing to accumulate to a dangerous level, the pressure in the cavity 20 pushes the valve member 76 outwards.This act unblocks the passageway 62, relieving the pressure by allowing fluid/vapor to flow to the upstream side of the piping system in which the valve 10 is interposed. In fully opening, the valve member 76 makes a protective metalto-metal back seat at 138/98 (FIGURE 3). If there is a possibility that this back seat may not be maintained with sufficient force, a compression coil spring (not shown) may be provided as part of the bypass valve, for tending to force the valve member 76 axially outwards.

By preference, as shown, the body of temperature-activated material 134 lies relatively exposed and relatively more vulnerable to being activated than would be the case were it buried deep within the housing of the valve 10.

There are some conceivable situations where bypass venting may be safer if made to the downstream side rather than to the upstream side of the piping system or the like in which the valve 10 is incorporated. For such a case, if the valve 1 0 itself is not subject to being mounted either way, an alterante model can be provided, wherein the safety feature 60 is provided to communicate with the downstream segment of the bore 14.

It should now be apparent that the apparatus improvement for safely relieving valve cavity pressure in the event of a fire in the vicinity of the valve as described hereinabove, possesses each of the attributes set forth in the specification under the heading "Summary of the Invention" hereinbefore. Because it can be modified to some extent without departing from the principles thereof as they have been outlined and explained in this specification, the present invention should be understood as encompassing all such modifications as are within the spirit and scope of the following claims.

Claims (4)

1. In a main valve having a housing provided with a throughbore, a valve cavity which intersects the throughbore and divides the throughbore into an upstream segment and a downstream segment, a valve member movably mounted in the valve cavity for movement between a closed condition, in which the valve member interdicts the throughbore between said upstream segment and said downstream segment and an open condition in which said throughbore is at least partially unblocked, so that the flow of a fluid through the valve may be controlled by moving the valve member between said conditions, an improvement for relieving valve cavity overpressure due to the accumulation of controlled fluid in the valve cavity and the valve being subjected to a high temperature event occurring in the vicinity of the valve when the valve is in or assumes said closed condition, said improvement comprising:: means providing a bypass passageway in said valve housing, said bypass passageway having an inlet port communicated to said valve cavity and an outlet port communicated to one said segment of said throughbore distally of said valve cavity; a normally closed bypass valve interposed in said passageway intermediate said inlet port and said outlet port; and heat-activated means disposed for vulnerability to the occurrence of a high temperature event in the vicinity of the main valve, and operatively associated with the normally closed bypass valve for permitting said normally closed bypass valve to open, upon heat-activation of said heat-activated means.

2. The valve improvement of claim 1 wherein: said main valve is a gate valve having gate plate expander means for forcing a valve gate means, provided as said valve member, tightly into blocking relation with said throughbore where said throughbore is intersected by said valve cavity, only when said valve gate means is in said closed condition.

3. The valve improvement of claim 2, wherein: said housing includes a body having a bonnet sealingly connected therewith, with the valve cavity being partly defined within the body and partly defined within the bonnet; a valve stem means connected to the valve gate means within the valve cavity and passing out of the housing through the bonnet, there being means sealing and joumalling the valve stem means with respect to the bonnet so that the valve stem means may be manipulated from outside the housing to shift the valve gate means between said open condition thereof and said closed condition thereof.

4. The valve improvement of claim 3, wherein: the bypass passageway is defined in said bonnet or in said housing.

4. The valve improvement of claim 3, wherein: the bypass passageway is defined in said bonnet.

5. The valve improvement of claim 4, wherein: the said one segment of said throughbore with which said bypass passageway communicates is said upstream segment.

6. The valve improvement of claim 1, wherein said bypass valve includes: said bypass passageway having means providing a valve cavity therein, having an annular valve seat; and a valve member movably mounted in this valve cavity, this valve member including a sealing surface adapted and positioned to seal with said annular valve seat; The heat-activated means comprising a body of material, the structural integrity of which is destroyed when the body is subjected to heating to a preselected temperature, said body being effectively associated with said valve member of said bypass valve as a shinto maintain said bypass valve member sealing surface sealingly engaged with said annular valve seat for so long as said body is not subjected to said preselected temperature.

7. The valve improvement of claim 6, wherein: said valve member of said bypass valve is mounted for axially sliding movement; said housing including a relatively thin-walled region covering said body of heat-activated material; said body of heat-activated material being axially interposed between said valve member of said bypass valve and said relatively thin-walled region.

8. The valve improvement of claim 7, wherein: said relatively thin-walled region is provided as a cap enclosing said body of heat activated material.

9. The valve improvement of claim 8, wherein: the bypass passageway communicates axially to said valve cavity of said bypass valve and said bypass passageway communicates generally radially from said valve cavity of said bypass valve; the bypass valve member comprising a rod having said sealing surface provided at an axially inner end thereof; said housing including an opening extending axially from the valve cavity of the bypass valve to the exterior of the housing; said rod having an enlargement disposed within this opening; valve stem packing means and packing activating means sealingly closing said opening about said rod axially outwardly of said valve cavity of said bypass valve; said cap being provided on said packing activating means;; said rod extending into said cap, wherein said body of heat activated material is axially interposed between an axially outer end of said rod and said cap.

1 0. The valve improvement of claim 9, further comprising: back seating means including an annular seat formed on said packing activating means at the axially outer end of said valve cavity of said bypass valve and a corresponding annular seat formed on said enlargement of said rod, these two seats normally being axially spaced, but being located to sealingly engage as said bypass valve member moves axially outwardly upon opening, in order to maintain said opening sealingly closed relative to the exterior of the housing even should said valve stem packing means be damaged.

11. Apparatus for safely relieving valve cavity pressure in the event of a fire in the vicinity of the valve having its parts constructed, arranged and adapted to operate substantially as herein described with reference to the accompanying drawings.

New claims or amendments to claims filed on 8 July 1982 Superseded claim 4 New or amended claim: