US3659624A

US3659624A - Fire safety valve

Info

Publication number: US3659624A
Application number: US25976A
Authority: US
Inventors: Warner M Kelly; John V Fredd
Original assignee: Otis Engineering Corp
Current assignee: Halliburton Co
Priority date: 1970-04-06
Filing date: 1970-04-06
Publication date: 1972-05-02
Anticipated expiration: 1989-05-02

Abstract

A heat responsive safety valve having a fusible material holding the valve at an open position. In one form the fusible material mechanically locks the valve open. In another form, the fusible material holds fluid pressure within a closed cylinder biasing a valve to its open position. In each form of the valve, the fusible material melts or otherwise weakens at a predetermined temperature releasing the valve to close shutting off flow through the conductor controlled by the valve as a firepreventing measure.

Description

United States atent 1151 3,659,624 Kelly et al. 1451 May 2, 1972 [s41 FIRESAFETY VALVE 2,137,685 11/1938 Gillen ..137/77 [72] Inventors: Warner M Kelly Houston; John 2,555,461 6/1951 Auguste ..137/72x Fredd, Dallas, both of Tex.

[73] Assignee: Otis Engineering Corporation, Dallas, Tex.

[22] Filed: Apr. 6, 1970 [21] Appl. No.: 25,976

[52] US. Cl ..l37/75, 137/72 [51] Int. Cl ..F16k 17/38 [58] Field of Search ..137/7277; 220/89 B; 169/19 [56] References Cited UNITED STATES PATENTS 998,507 7/1911 Hasty 1 37/76 Primary Examiner-Alan Cohan Assistant Examiner-Richard Gerard Attorney-H. Mathews Garland [5 7] ABSTRACT A heat responsive safety valve having a fusible material holding the valve at an open position. In one form the fusible material mechanically locks the valve open. In another form, the fusible material holds fluid pressure within a closed cylinder biasing a valve to its open position. In each form of the valve, the fusible material melts or otherwise weakens at a predetermined temperature releasing the valve to close shutting ofiflow through the conductor controlled by the valve as a fire-preventing measure.

2 Claims, 8 Drawing Figures FIRE SAFETY VALVE This invention relates to safety devices and more particularly relates to a fire safety valve for a flow line.

Flow conductors in well heads, pipe lines, and the like are particularly susceptible to fire, especially when they are carrying flammable fluids such as oil and gas. When fire occurs due to a leak in such a conductor, or in the vicinity of such a conductor and its valves, damage is minimized by an immediate closing of such valves. Conventional valves have no means for closure responsive to temperature, and, of course, if within a fire area, often cannot be reached to be manually closed. Also, conventional valves often contribute to a fire hazard in the sense that the packing in such valves may be sufiiciently damaged by a fire that the valve itself becomes a contributor to the hazard with flammable fluid leaking outwardly feeding the fire from the valve. While many systems have been employed in the past to detect and function responsive to fires, they generally are somewhat complex in nature, expensive, and may be subject to malfunction.

It is an especially important object of the invention to provide a new and improved safety device to provide protection against fire hazards.

It is an especially important object of the invention to provide a new and improved safetyvalve operable responsive to exposure to a fire.

It is another object of the invention to provide a fire safety valve which is mechanically held at an open position by a fusible material and released for movement to a closed position responsive to the melting or destruction of such material by a fire or exposure otherwise to a temperature above a predetermined level which might effect a fire in a system including the safety valve.

It is another object of the invention to provide a gate type valve locked open by a collet which is expanded to release such valve for movement to its closed position and which is held against expansion by a fusible ring.

It is another object of the invention to provide a gate type valve held at an open position by a compressible collet held at its normal position by a fusible member and released for compression to allow the valve to close.

It is a still further object of the invention to provide a fire safety valve of the gate valve type having'a valve stem held by a locking cap connected with the valve body by a fusible bushmg.

It is another object of the invention to provide a fire-safety valve held at its open position by pressure within a chamber enclosing a piston connected with the valve stem, such pressure being releasable through a fusible plug connected with the chamber wall.

These and other objects of the invention will be apparent from reading the following description of fire safety valves embodying the invention taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a view in section of a gate valve mechancially locked at an open position by safety apparatus embodying the invention;

FIG. 2 is an enlarged fragmentary view in section of the safety locking device shown in FIG. 1;

FIG. 3 is a view in section of another type of safety valve and a locking device embodying the invention holding the valve at its open position;

FIG. 4 is an enlarged view in section of the collet type fireresponsive locking device shown in FIG. 3;

FIG. 5 is a view in section along the line 55 of FIG. 4;

FIG. 6 is a view in section of a still further form of fire safety valve and locking device embodying the invention;

FIG. 7 is an enlarged fragmentary view in section of a modified form of fire-safety device on a valve similar to that of FIG. 6; and

FIG. 8 is a fragmentary view in section of a modified fon'n of the valve shown in FIG. 7.

In accordance with the invention in one form of firesafety valve locking apparatus embodying the invention an expandable locking collet is held by a fusible ring around a locking head on the stem of a gate valve biased by line pressure downwardly toward a closed position. In another form of fireresponsive safety locking apparatus useful with a gate valve, a contractible collet is held at a normal position by fusible material which melts or weakens responsive to temperature to permit the collet to contract to allow the valve stem to move into the collet for shifting the valve to its closed position. In a still further form of fire safety valve embodying the invention, a locking cap is threaded by an internally and externally threaded locking bushing of fusible material holding the valve stem at a closed position until the locking bushing is subjected to a predetermined temperature. In a still further form of valve embodying the invention, the valve is held at its open position by pressure within a chamber released by a fusible plug responsive to a predetermined temperature.

Referring to FIG. 1 of the drawings, a gate valve 10 constructed in accordance with the invention includes a body 11 having flanges 12 and 13 for connection of the valve into a flow line. The valve is generally similar in structure to the Type X Otis Surface Safety valve illustrated in and described at page 3832 of the 1968-69 Edition of the The Composite Catalog of Oil Field Equipment and Services, published by World Oil, Houston, Texas. A piston assembly 14 mounted on the valve body includes a body member 15 having base mounting flange 20 secured on the valve body 11. The piston assembly body 15 has a cylinder chamber 21 vented to the atmosphere through a bleed port 22 at the lower end of the cylinder. A gate valve 23 is slideably disposed in the body 11 in a pocket 23a for vertical movement between open and closed positions. The gate valve has an opening 24 which registers with the flow passage 25 through the valve body when the valve member is at the open position illustrated in FIG. 1. The gate valve has a lower stem 30 connected at its lower end with the gate valve and provided with a piston 31 slideably disposed within the cylinder 21. Suitable packing 32 is disposed at the base of the body 15 around the lower valve stem to prevent leakage from the valve body around the valve stem. A ring seal 33 is supported around the piston 31 to seal within the chamber 21. The lower valve stem and valve is provided with a vertical flow passage 34 which opens at its lower end into the port 24 through the valve and communicates at its upper end with a lateral flow passage 35 provided in an upper valve stem 40 extending above the piston 31. The upper valve stem has a locking head 41 defined above an-external annular locking recess 42 in the stem. A ring seal 43 is disposed in an external annular recess in the head of the body 15 to seal around the upper valve stem 40 above the piston 31.

' In accordance with the invention, the valve 23. is locked at its upper open position as shown in FIG. 1 by a fire safety locking assembly 44 which comprises a locking collet 45 and a fusible locking ring 50. The locking collet has a base ring 51 from which a plurality of circumferentially spaced locking fingets 52 entend upwardly. Each of the locking fingers has an internal locking boss 53 received within the locking recess 42 below the locking head 41 of the upper valve stem for locking the valve stem against downward movement, FIG. 1. Each of the locking fingers has an external recess 54 at its upper end generally aligned with the internal locking bosses 53. The fusible locking ring 50 is received in the recesses 54 of the locking fingers holding the fingers against radial expansion. The locking ring 50 is fonned of a material which readily reacts to a predetermined temperature level causing it to either disintegrate by melting or to weaken sufiiciently that it loses the structural strength to hold the locking collet against the expansion of its fingers. The locking ring may be made of such metals as lead, solder, a low temperature melting metal sold under the trademark Serrocast. Preferably, the melting temperature of the locking ring 50 is Within the range of about 350 to 450 F., as any temperature above this range is going to provide a dangerous environment to the fire safety valve and the flow system of which it is a part. The safety ring, of course, may also be formed of a fusible plastic which has suflicient strength to resist the normal forces applied to the locking collet while breaking down either by melting or by reduction of its strength to permit it to stretch sufficiently at the desired temperature to release the locking collet.

During normal operation of the valve at its open position as shown in FIG. 1, the locking collet 44 is disposed around the upper valve stem 40'with the base ring 51 of the collet resting on the top of the housing and the collet finger bosses 53 engaged in the locking recess 42 around the upper valve stem. The locking ring is positioned around the locking finger heads as shown in FIGS. 1 and 2 preventing expansion of the heads so that the locking bosses 53 prevent downward movement of the valve stem and locking head 41 thereby holding the valve at its upper open position. The cylinder 21 is exposed to atmospheric pressure through the bleed port 22 below the piston 31 while line pressure within the flow passage 25 of the valve is communicated upwardly through the flow passage 34 in the valve stem and the lateral passage 35 above the piston so that line pressure is within the cylinder 21 above the piston 31. This line pressure, being greater than the atmospheric pressure below the piston, urges the valve stem and valve 23 downwardly against the holding force of the fire safety valve lock 44. If the valve is subjected to fire or is in sufficient proximity to a fire to raise the temperature at the locking ring 50 above the desired predetermined value, the ring 50 melts, or if a plastic, loses its structural strength to the degree that the downward force of the line pressure above the piston 31 overcomes the collet camming the collet locking bosses outwardly thereby releasing the locking head 41 on the valve stem so that the line pressure above the piston 31 forces the valve stem downwardly moving the valve member 23 to its lower closed position at which the port 24 through the valve member is below the flow passage 25. The nature of the structure of the valve 23is such that it is forced to the downstream side of the valve member pocket 23a in the valve body sealing against the surface of the pocket on the downstream side around the opening 24 precluding flow past the valve member, while on the upstream side of the valve there is sufiicient tolerance to permit upstream line pressure to continue to be communicated up through the valve stem flow passage 34 above the piston 31 to hold the valve at its lower closed position. When the heat or fire condition no longer exists, the valve may be returned upwardly to its open position by use of a suitable pulling tool, not shown. The locking collet is reset around the locking head of the valve stem and a new locking ring 50 installed around the heads of the collet fingers to again hold the valve releasably locked open and responsive to temperature conditions for again closing in the event that heat conditions raise the temperature in the vicinity of the valve as above described.

FIG. 3 illustrates a similar type of valve 60 which is locked at its lower open position and movable upwardly to a closed position. The valve 60 has a body 61 provided with a flow passage 62 and

suitable flanges

63 and 64 for connection of the valve in a flow line. A valve 65 having an opening or port 70 is movably disposed in a valve pocket 71 of the valve body for movement between a lower open position as shown in FIG. 3 and an upper closed position, not shown. The valve has a cylindrical valve stem 72 which extends upwardly into a locking assembly housing 73 supported on the valve body by an integral flange 74. A suitable seal assembly 75 disposed in the housing 73 around the valve stem seals against leakage along the valve stem from the valve body. A heat responsive safety release assembly 80 embodying the invention is releasably disposed in the housing 73 holding the valve stem 72 at the lower end valve-open position as shown in FIG. 3. The safety assembly is held in the housing by an annular retainer cap 81 having an internal annular locking surface 82 for holding the assembly at its locking position. The lower end of the cap 81 along with the inner surface of the housing 73 below the cap 81 defines an internal annular collet release recess 84which performs a releasing function when the lock assembly 80 responds to temperature and is forced upwardly by the valve stem.

The fire safety assembly comprises a collet 85 having integral longitudinal fingers defined between downwardly opening circumferentially spaced longitudinal slots and alternate upwardly opening circumferentially spaced longitudinal slots 91, FIG. 5, whereby the collet is expandable and compressible at both its upper and lower ends. The collet finger upper end portions have external locking bosses 92, while, similarly, the lower collet finger end portions have external locking bosses 93. The upper collet finger end portions are provided with internal recesses 94 aligned to define an internal annular recess in the head of the collet through which is disposed a fusible locking disc 95 for holding the upper end portion of the collet against compression until a predetermined temperature level is reached which the locking disc melts or otherwise is weakened sufficiently to no longer have the structural strength to hold the upper end portion of the collet against compression. It will be recognized that, if desired, instead of a locking disc an internal annular ring, such as the ring 50, may also be used disposed through the slots 94 to hold the collet against compression. The lower free end portions of the collet fingers have internal locking surfaces or inner bosses 101 which are engageable with a tapered upper end portion 72a of the valve stem, see FIG. 3. The upper end portions of the collet fingers have sloping locking surfaces 102 engageable with the internal annular licking shoulder 82 in the retainer cap 81.

The operative position of the fire safety lock assembly 80 is illustrated in FIG. 3 at which the assembly releasably holds the valve member 65 at its lower open position to permit flow through the valve passage 62. The lower locking collet head surfaces 100 engage the locking shoulder surface 720 on the upper end of the valve stem. The lower collet locking finger bosses 93 are confined at the normal radial positions shown in FIG. 3 by the internal housing surface defining the lower bore 73a of the housing 73 below the collet release recess 84. The internal locking shoulder 82 of the retainer cap 81 is engaged by the locking surfaces 101 on the upper end of the collet holding the collet against upward movement. The line pressure within the valve flow passage 62, effective across the sealed area of the valve stem defined by the seal 75, exceeds the atmospheric pressure on the stem above the seal 75 whereby the valve stem and valve 65 are biased upwardly by line pressure toward a closed position. So long as the temperature remains below the level at which the disc 95 melts or substantially weakens, the locking assembly 80 holds the valve at itsopen position as shown in FIG. 3.

When the valve 60 is exposed to a temperature above the desired predetermined level, either by direct flame or being in the proximity of a fire, the safety disc 95 either disintegrates by melting or the strength of the disc is sufficiently reduced that it no longer is capable of supporting the upper end portion of the fingers of the collet 85 at their normal positions against the inward camming effect of the retainer cap surface 82. The upward force of the upper end of the valve stem against the lower collet surfaces 100 urges the collet upwardly so that the coaction between the upper collet surface 102 and the locking shoulder 82 of the retainer 81 cams the upper end portions of the collet fingers inwardly. The collet fingers are forced upwardly and compressed inwardly past the locking surface 82 and outwardly through the upper end of the retainer. Simultaneously, the upper valve stem end surface 72a carns the lower ends of the collet fingers radially outwardly expanding them into the cam release recess 84 whereby the valve stem is released to move upwardly into the lower end of the collet permitting the valve to move to the fully closed position. Line pressure will continue to be applied to the valve and stem holding the valve upwardly at the closed position. The valve 65 is similar to the valve 23 of FIG. 1 and seals on the downstream side against the downstream surface of the valve pocket 71 with sufficient tolerance at the upstream side of the valve to permit line pressure to be applied over the valve and stem holding the valve at the upper position.

The valve 65 is reset by use of a suitable closing device, not shown, including a probe or rod for engaging the upper end of the valve stem to force it to back downwardly reopening the valve. The locking collet is removed from the housing 73 by unscrewing the retainer cap 81 and lifting the collet upwardly. The fire safety locking assembly 80 is reset by inserting a new safety disc 95 into the upper end of the collet by expansion of the collet fingers sufficiently to manipulate the disc into the recesses 94. After replacement of the safety disc, the collet is reinserted to the position shown in FIG. 3 and the cap 81 is reengaged in the top of the housing.

A still further form of fire safety valve 110 is illustrated in FIG. 6. The valve 110 is normally a pressure responsive valve controllable from a remote location by fluid pressure. The valve has a body 111 provided with a flow passage 112 and

flanges

113 and 114 for connection into a flow line. Flow through the passage 112 is controlled by a gate valve 115 having a part 120 and connected with a valve stem 121 which extends upwardly into a pressure chamber 122 provided within a vessel 123 secured on a base 124 by a lock ring 125. A valve stem guide flange 130 is formed integral with a base 124 and provided with a ring seal 131 which seals around the valve stem within the guide flange. The base 124 is secured by a plurality of bolts 132 to the valve body 111. A coil spring 133 is confined between the plate 124 and an annular piston 134 rigidly secured, as by welding, on the valve stem in the chamber 122. A ring seal 135 around the piston seals within the cylinder chamber. The cylinder chamber is vented to the atmosphere below the piston by a bleed port 140. An upper end portion of the valve stem 121 extends through an externally threaded nipple 141 formed on the head end of the vessel 123. A ring seal 142 in an internal annular recess of the nipple 141 seals around the stem 12] so that pressure may be maintained in the cylinder 122 above the piston 134. A conduit 143 containing a valve 144 is connected into the head of the cylinder 123 to provide fluid pressure for holding the piston 134 downwardly against the spring 133 to maintain the valve 1 15 at the open position shown in FIG. 6. A valve similar to that of FIG. 6 is an Otis Type U Surface Safety Valve illustrated at Page 3834 of the Composite Catalog of Oil Field Equipment and Services, supra. The conduit 143 may be connected to a controllable source of fluid pressure which reacts responsive to any desired condition, such as excessive heat which would relieve fluid pressure within the chamber above the piston to allow the spring to lift the valve to its closed position.

In accordance with the invention, the valve 115 is locked at its open position by an internally threaded cap 145 secured on the nipple 141 over the upper end of the valve stem 121 by a fusible internally and externally threaded bushing 150. The bushing is provided with a lower external annular end flange 151 for gripping the safety bushing when threading it on the nipple. So long as the fusible safety bushing is intact, the cap 145 engages the upper end of the valve stem 121 holding the valve open in such a manner that it is closable only when the valve is enveloped in a fire or sufiiciently close to a fire that the flow system including the valve is endangered. The heat from such a fire or nearby fire melts the fusible bushing or sufficiently weakens it that the force of the spring 133 can lift the valve stem to close the valve. The upper end of the valve stem forces the cap 145 off the nipple 141. It will be apparent that coincident with the release of the valve stem by the fusible safety bushing, the fluid pressure within the cylinder 122 above the piston 134 must also be reduced to permit spring action and line pressure to close the valve. The fire safety system on the valve 1 is generally used only under special operating conditions of the valve where it is desired that the valve be restrained against closing in the event of a malfunction of the fluid control system. An example of such an operating condition is encountered when the valve is used as a master valve in a well head and wireline operations are being carried out in the well through the well head. In this situation, if the valve were permitted to suddenly close responsive to some failure or malfunction of the pressure control system of the valve supplying the fluid into the chamber 122, the valve would suddenly close cutting the wireline passing through the valve flow passage 112 and the port in the valve 115. Such an accident could necessitate substantial expense in retrieving the wireline and equipment connected thereto. While it is desirable under such circumstances to protect the valve against a control fluid pressure malfunction, it is further desirable that in so protecting the valve it not be restrained against closure in the event of fire. Thus, during wireline operations the valve is locked open by the cap secured on the nipple 141 by the fusible safety bushing 150. When a wireline operation is completed and the wireline is withdrawn through the valve, the valve is returned to normal fluid pressure responsive operation by unscrewing the locking cap 145 and the fusible bushing from the nipple on the cylinder body.

A modified form of pressure responsive valve is illustrated in FIG. 7. The valve 160 is similar to the valve 110 of FIG. 6 in structure and operation. The body of the valve 160 may be identical to the valve body 111 with the base portions of the cylinder body 161 of the valve 160 being identical to that of the body 110. The valve stem 121a of the valve 160 is secured to and terminates in a piston 134a which carries an external ring seal 135a for sealing around the piston in the cylinder of 162 of the housing 161. A spring 133a biases the piston upwardly to lift the valve member of the valve to a closed position in the event of failure of pressure within the cylinder above the piston. Control fluid pressure is communicated through a conductor 163 containing a valve 164 into the cylinder chamber from a remote fluid control unit, not shown.

In accordance with the invention, fire safety assembly is secured through the head of the cylinder body 161 to relieve the fluid pressure in the cylinder in the event of fire or excessive heat exposure. The safety device 170 includes an externally threaded nipple 171 provided with a fusible core 172 extending the full length of the nipple within the longitudinal bore of the nipple. Upon destruction and thus expulsion of the core from the nipple, the cylinder chamber 162 is communicated through the bore of the nipple to the atmosphere. In operation, the valve 160 is normally held at its open position by the pressure of the control fluid communicated into the cylinder chamber through the conductor 163. If the valve is subjected to excessive heat, the fusible plug 172 of the nipple melts thereby releasing the control fluid pressure from the cylinder above the piston 134a permitting the spring 1330 and line pressure to lift the piston to close the valve. A plurality of plugged nipples 171 may be circumferentially spaced around the top of the vessel 161 to provide a safety device near a fire approaching from any direction around the valve.

A still further form of valve embodying the invention is illustrated in FIG. 8. The valve 180 is similar to the valve 160 of FIG. 7 and includes certain identical parts denoted by the same reference numerals as used in FIG. 7. The general structural arrangement of the valve is similar also to the valve 110 in FIG. 6. The cylinder body 181 has a nipple 183 formed integral with its top. The nipple is provided with a stepped bore comprising a first upper bore portion 184 and a connecting reduced lower bore portion 185 opening into the chamber 182 of the cylinder. The chamber 182 is initially charged with a suitable fluid to a pressure sufficient to hold the piston 134a at a lower valve-open position and the bore portion 184 is filled with a fusible plug sealing the fluid in the chamber. The ring seal 135a prevents leakage past the piston. When the plug 190 is heated to the breakdown temperature of the fusible material, the plug is expelled from the nipple bore releasing the fluid pressure in the chamber allowing the spring 133 a and line pressure to lift the valve to a closed position. The valve may be opened and reactivated by repressuring the chamber and replacing the fusible plug 190. If desired, a plurality of the nipple-fusible plug safety devices may be used in the cylinder so that the valve is sensitive and responsive to more localized heat sources around the valve.

It will now be seen that a new and improved form of fire safety valve has been described and illustrated for use in flow lines included in such apparatus as well heads, pipe lines, and v the like. Fire safety valves embodying the invention in one form utilize a mechanical lock releasable responsive to a predetermined temperature level, while in other forms, the safety device comprises temperature responsive pressure release means, both utilizing fusible material for releasing ag, valve for closure when overheated. The mechanical form of the apparatus is applicable to gate valves which close downwardly'and also to those which close upwardly. In the first instance, the device includes an external collet arrangement which holds the valve against downward movement until overheated, while in the second arrangement an internal collet is utilized to hold the valve against upward movement until overheated. The new and novel safety devices are not susceptible to accidental triggering so that they release only in response to excessive temperature conditions.

l. A fire safety valve comprising: a valve body; a valve movable between open and closed positions in said body; means biasing said valve toward said closed position; a housing on said valve body, said housing having an internal annular surface portion defining a locking shoulder and an enlarged internal annular surface portion defining a collet release What is claimed and desired to be secured by Letters Patent 2 recess; a stem on said valve having an end portion extending into said housing; and means for holding said valve at said open position including a compressible locking collet releasable disposed in said housing, a first end of said collet engaging said end portion of said valve stem in said housing for holding said stem against movement toward said closed position of said valve, a second compressible end of said collet engaging said locking shoulder in said housing, said second end of said collet being releasable from said shoulder responsive to inward camming action of said shoulder on said collet compressing sg id collet inwardly and fusible means Within said second end of said collet and responsive to a predetennined temperature holding said second end of said collet against compression and release from said locking shoulder whereby said collet holds said valve stem against movement toward said closed position of said valve until said fusible means releases said collet responsive to said predetermined temperature to permit said locking shoulder to compress said second end of said collet for movement past said locking shoulder and said 0 first end of said collet to move into alignment with said release recess of said housing to allow said stem to move to said valve closed position.

2. A valve as defined in claim 1 wherein said collet has an internal annular recess in the upper end thereof and said fusible means in a disc disposed in said annular recess.

l l I

Claims

1. A fire safety valve comprising: a valve body; a valve movable between open and closed positions in said body; means biasing said valve toward said closed position; a housing on said valve body, said housing having an internal annular surface portion defining a locking shoulder and an enlarged internal annular surface portion defining a collet release recess; a stem on said valve having an end portion extending into said housing; and means for holding said valve at said open position including a compressible locking collet releasable disposed in said housing, a first end of said collet engaging said end portion of said valve stem in said housing for holding said stem against movement toward said closed position of said valve, a second compressible end of said collet engaging said locking shoulder in said housing, said second end of said collet being releasable from said shoulder responsive to inward camming action of said shoulder on said collet compressing said collet inwardly and fusible means within said second end of said collet and responsive to a predetermined temperature holding said second end of said collet against compression and release from said locking shoulder whereby said collet holds said valve stem against movement toward said closed position of said valve until said fusible means releases said collet responsive to said predetermined temperature to permit said locking shoulder to compress said second end of said collet for movement past said locking shoulder and said first end of said collet to move into alignment with said release recess of said housing to allow said stem to move to said valve closed position.