GB2531265A - A frangible plug for use in a valve mechanism - Google Patents

Abstract

A frangible plug for use in a valve mechanism comprises a first section 1 having a first end 13 and an opposing second section 2 having a second end and a cylindrical sidewall 16 extending between the first and second ends. A shape memory alloy wire 100 extending circumferentially around the outer circumference of the sidewall 16 applies a force on the sidewall 16 of the frangible plug such that the first section 1 fractures from the opposing second section 2.

Description

A FRANGIBLE PLUG FOR USE IN A VALVE MCI1ANISM

BACKGROUND

u1 A frangib'e plug for use in a valve mechanism, and, more parliculariy, a singeuse vaIe rnecha iism thet may be used fe discharging uid is desonbed here!n The frangible pLig and valve mechan am may have particular ise in the field of suppressant r&ease, such as a fire suppressant fluid.

[2] The examples described herein relate to devices and methods for the controUed release of a fluid flow substance. They are particularly suited, hut not imited, to the controlled release of a suppressing or extinguishing agent from a cyhndoi The devices and methods described may further bc used for the rapid deployment of an extinguishing agent from a cylinder, such as those that may typical y, although not eclusiely, be used on moviny platforms suc'i as aircrafts trans, military or commercial vehicles.

[3] Such valves faU into two main groups; nonhermetic and hermetically sealed The tormor category is typified by the high rate discharge HD) vaN/es used on suppressors n rulitary and commercia vehicles These can be electromechanical or protractor fi cd consisting of either a flapper or poppet as the main openings mechanism Both systems contain mtdt pie mos'inq components anc rely on O-nng seals for integri'c Such valves cc i be i&atively expensie and require refurbishment prior to use.

[4) Further appcations, such as aerospace, require that the suppressor be hermetically sealed to rnnrnise eakago over the requiiod ens,ironmenta range end to extend service life. Such hermetically sealed extinguishers use an explosive cartndge located on the outside of an cuBe diaphragm, which upon actuation ruptures a disc and releases agent into a distnbution network o directly into the protected fire zonc This method although very fast and relable, IS oronc to fragmentaon of the diaphragm during actuaon and requres the use of pyrotechnic cartridges. These valves require periodic maintenance arid reolacement and have associated handiing, transit and storage restrictions 5j The examples described herein aim to retain the rapid opening and free flow characteristics of the pno ar whElst reducing cost, removing pyroecbnc caindgec and provding the optic' for herrnthcity where requiied [6] DE 19736247 discloses a component having a body made of brittle material and the use of pieioelectnr ements both embedded and laminated into t'ie body such that when the body s energized by the piezoolectnc elements, a portion of the component s destroyed.

[7] US 2010/025050 discloses a thermally activated sprinkler vve that includes a shapememory element that expands as it is heated, forcing a boll to break, thereby opening the sprinkler valve.

[81 US 6682521 describes numerous methods of opening a pressure containing vessel through the use of memory shape alloys.

[9] European Patent Application No 141600L0 cisclnses a ceramic disc with a pi ede1ired stress plane Nhich is fractured by impac by a point force rvleans for braze attachment of the disc, means for minimising fragmentation and a means for reta fling te tree section of the disc after fracture are also disclosed [10] EP I h82789 describes dev ces and methods for controlling the eleass of 3 substance which are particularly suited to the control ci substances such as fire extinguishing media The devices and methods described comprise a housing havng an inlet to" connection to a source of a substance and an oullet with a passage extending therebetween The passage may be closec by a frangible element wnic' comprises a ceramic' disc that is cmrieoted to a source of electrical current. The disc may be a metal oxide ceramic dsc, and may be fractured by an Sectrical pulse which is applied to the disc.

i GB 1378079 describes a bursting disc assembly, and in parficular a vessel havng an aperture sealed by the bursting disc assembly The bursting thsc assembiy is compnsed of toughenod giass that is shattered by a movablo spike which is projected against the glass with sufficient force to rupture the surface layer thereof and consequently shatter the disc. The spike is moved via pressure created by the ignition of a pyrotechnic composition.

[12] GB 567120 discloses a quick-release valve arrangement for a container of fluid under pressure which is aimed at enahhng fuid to be released in a simple and rapid manner. The valve arrangement comprises a hoflow body or casing formed with a valve seat as wefi as a ye vs that is shaped to fit upon the valve seat to seal up the passage leading from the fluid container. A frangible disc, which may be fo'med from cast von, pottery, glass or briftie plastic, a located within the valve body and spaced from the valve proper by a strut member which serves to hold the valve down on ta seat The dewce alo includes a p unger that is used to sha.ter the disc and release the valve. The disc may also be shattered in other ways such as by prey ding an eplosivo charge or via a small projectile driven by to oxplosion striking the disc.

[13] US 77O3471 discloses a remutelyoperated sngle-acf ion discharge valve for releasing gaseous liquid, or dry material from a pressurized storage vessel. A frangible seal is provided within a alve body which seals the passage therethrough when the seal is intact. A solenoid is described which includes an armature moeable from a first position to a second position when the solenoid is actuated The device includes a tooth, teeth or a pin or plurality of pins which Dreac the frangible seal as the armature moves between the f rat and second position Thc seals described are held in place using an oring and can be made of glass.

SUMMARY

[14] In one example, there is provided a frangible plug for use in a valve mechanism the Irangible plug comprising a first section having a first end and an opposing second section having a second end and a cylindrical sidewall extending between the first and second ends. and means for applying a force on the cs.hndrical sidewall of the frangible plug such hat the first section fractures from the opposing sec,ond section, ana wherein the means for applying a force on said cylindrical sidewall exterds circumferontially arxind the outer circumference of the sidewall. .4.'

[15] Further, the means for app}yThg a force on the cylindrical sidewall of the frangible plug may be actuated on appcaUon of heat.

116] The means for applying a farce on the cyVndrical sidewa of the frangible plug may be a shape memory alloy actuator.

fl71 Further the shape memory aoy aruator may coripnse one or more shape memory alloy wftes, [18] The one or more shape memory alloy wres are crimped or welded to each other & a po ni adjacent to the sidewall of the frangible plug (19 The sha,ie memory alloy actuator may further comonse one or more secondary metal wfres, [20] [urther, a groove may be formea in the sidewall and wherem the shape memory alloy actuator is positions in said groove.

[21] In a further example, the frangible plug further comprises a recess having an open end at the second end of the plug; and wherein said plug comprises a predefined fracture plane and wherein said plug is configured to fracture across saa p'edefined fractui o plane and wherein saio predefined fracture plane extends around the outer circumference of the sidetail, and a closed end, with,n the plug, wth an inner surfac1e of th cyirdrical sidewall extending therebe-ween, said predefined fracture plane intersecting the sidewall within the recess to provide the predefined fracture line that extends around the inner circumference of the sidewall of the frangible plug.

[22] Further a groove may be formed in the predefined fracture p ane and where n the one or more shape memory alloy wwes s positioned in the groove [$31 The groove may be located in the first section adjacent the first bevelled portion.

[241 The diameter of the recess may be smaller at the closed end of the recess than at the open end of the recess and the outer surface of the sidewah has a first Devefled portion and the inner surface oF the sidewaD has a second bevelled portion, ard wheren a part of the bev&led portion of thc outer surface that has the sma lest diameter may laj in the same plane as a part of the bevelled portior of the inner surface that has the greatest diameter, [25] In another exampe, there is provided a valve mechanism comprising a valve body having an inlet port and an outlet port and a passageway extending therebetween and a zranglhle plug as descnbed above, wherein the plug is h&d within the valve body such that the plug blocks the passageway when intact and wherein, when the tangible plug is fractured, fluid flows from the inlet port to the ouflet port.

[26] Further, The first end of the franib!e plug may be in flow communication with the outlet port and the second a d at the frangible plug may be in flow communication with the inlet port.

BRIEF DESCRIPTION OF THE DRAWINGS

[27 Examples of an improved frangible plug for t a in a valve meenanism and a vavo iethaniam are herein described with reference to the accompanying drawings, [26] Figure IA shows a view of a frangible plug.

[29] Figure I B shows a view of a section k-A of the frangible plug of Figure IA.

[30] Figure IC shows a detailed view of section B of the frangible plug of Figure 16.

[31] Figure ID shows, via Finite Element Analysis (FEA) the prindpal stress distributior of the Iug spawn in Hg ires IkIC when a unifo"rn cressure is apped o the part of the plug thr s in flow communication wth an inlet port of a vahie 132] Figure 2 shows a view of a shape memory alloy and crimping means.

[33] Figures 3A and 38 show alternative shape memory alloys to that shown in Figure 2.

34] Figures 4A and 48 show alternative shape memory alloys to those shown in Figures 2, 3A and 38.

[35 Figures 5A and 53 show a valve methanism including the frangible plug of Figures lA-iC.

DETAILED DESCRIPTION

[36] In general a frangible plug 10 is provided between an inlet port to an outlet port of a valve mechanism (described later). The frangible plug prevents fluid from flowing through a conduit until it is activated, by forming a scsi across the valve between the inlet and outlet ports. When the frangible plug is activated, fluid can flew through the conduit From the inlet port to the oudet port of a valve mechanism [37] Gonerafly t'e frangible pluq 0 has a cylindrical sidewafl anc, thrcumferentia ly exteidng around the cyhndrical sidewall, a piovided a means for aoplyn d force o the cyhndnca sidewall of the plug Wien the means or applying a force to "ic plug is activated, the frangible plug fractures such that fluid ma flow through the conduit from the inlet port to the oudet par 8] An example at a frangible plug is shown n Figures IA-iC but it is envisaged that the plug may be shaped other than a top hat arrangement discussed below. What is important is that the frangible plug has a means for applying a force to a cylindrical sidewall of the plug and that the means for applying the force circumferentially extends around the cyiinddcal sIdewall.

[39] The frangible plug descdbed herein may be formed from a brittle ceramic material for exarnDle alumina bLt may also be formed from any simi arly brittle vitreous or polymeric material. 2'2

(401 One example of a frangible plug described herein and shown in Figures 1A IC is in the general shape of a top hat', In this example, the plug a seen as having a continuous, dosed first surface 13 which is enerally flat at the first end 14.

Although the first surface of the plug is described herein as being flat, this is not necessary and tie surface could be any other siapo such as curved, or dome shaped. The plug also has an opposing second end 12. The outer perimeter of the surfaces at the hrst and second ends 14 and 12 are generaly crcular n tns embodiment, however, other shapes could be used, depending on the chosen desgn The plug further has a sdewaH 16 wUh an outer surface 30 whch extends cyhndncally between the first and second opposnq ends, 14 and 12 [41] As seen in Figure lÀ, the plug has a first section 1 which includes the first end 14 end a second section 2 which includes the second end 12, [42J In detaiL the outer surface 30, of the sidewall 16 of the plug shown in Figures 1#IC comprises three portions, 15, 17, and 19, each with different diameters and therefore circumferences to each other. As can be seen in Figures IA4C, here s a porhon of substa ihslly unforni d'amete and cwcumference at either end of the plug, 17 and 19, with a first angled or bevelled portion, or flange, of ncreasngIdecreasmg damoter therebeeen 15 The cwcu fererce cf The cyndrical portion at the second end 12 is also greater than that of the first end, ierehy c cating what would be the hnrn' of' no top hat' shaoe Although the erd pcrhons of the outer surface of the sdewa of the example snown neren are of generally unrform darnefer, the thanieter does not have to be completely unrtorm flc t' j [43] A second portion 15 of the sidewall 16 which is connected to the first portion 17 is bevelled and extends at an angle outwardly from the first portion 17 thereby comprising an increasing diameter in the direction 18 of the second end 12, The second porhon 15 contacts the thrd porUoi 19 wnC s gan generally unftorm n diameter and cylindrical in shape and also extends generally parallel to the first portion 17 of the outer side wall. This third portion 19 therefore constitutes a flange, or the brim' of the top hat' shape and in the example shown has a generally uniform diameter. The outer diameter of the sidewall 161s at its greatest in the third portion 19, [44] The first section 1 of the pRig includes the first portion 17, The second section 2 of the pRig indudes the second portion 15 and the third portion 18.

F45] As described above, the plug has a first, closed continuous surface 13 at a S flrst end 14 however, the opposing second end 12 of the plug defines an opening to a cyllndricai recess 22 extending into the pug, which is seen in Figure 15 as being positioned approximately in its centre.

[46] As seen, for example, in Figure 1 B, the recess 22 has an open end 26, at the second end 12 or the plug, a dosed end 20 within the pRig, and an inner surface 23 of the c'hndncal sidewall 16 extending thorobetween As can be seen in Figure 16, the diameter and circumference of the cylindrical wall at the closed end of the recess is smaPer than the ciameter and cit cumforence of the wall at the open end 2$.

[47) In greater detail the cvhndrical recess 22 is formed by tie sidewal a having an inner surface that extends from the second surface 11 at the second end 12 of the plug in the direction of the first end 14. The inner surface, or sidewafl 23 wfthin the recess of the plug comprises a first portion 24 which extends cylindricafly and is of generally uniform diameter from the second arid 12 and second surface 11 of the plug I his first portion 24 of the inner surface of the sidewad also extends in a direction that is generally parahei to the end portions, 17, 19, of tie outer surface of thc sidewall, as desrribed above, aithougn this is not necessary The in er surface 23 of the sidewall also comprises a second portion whc' is eveed 21 wherein the diameter decreases in the direction ci the t'rst end 14 of the plug and the surface 25 at the closed end 20 of the recess 22.

[48] The recess therefore terminates in a closed end 20 having a surface 25 that has a smaller diameter and circumference than the open end 26 of the recess at the second surface 11. In the figures, the surface at the closed end 20 of the recess 22 is shown as being flat, however, this is not necessary and any shaped surface can be used.

[49] As described above, the oiter surface of the sidewall 16 has a first beveiled portion 15 and the inner surface 23 of the side wall has a second bevelled portion [50] As can he seen the figures, the part ci the bevelled portion of the outer surface triaL has the smallest diameter es in the same pane as the part of the bevelled portion of the inner surface that has the greatest diameter.

[51] The above describes an arrangement of a "top hat" shape frangible plug, but it is envisaged that other arrangements and shapes could be used in conjunction with means for ppling a force on Vie cyhndncal sidewall described below What is important is that means for applying a force on the cylindrical sidewall provides a break n the seal to allow flu to flow from the inlet port o the ouflet port 52] As shown in Figures IPk IC, the rangthle plug aiso compnses means 100 for apply ng a force on the cyhndncal sidewal, 16, of the plug such that the first section, 1, fractures from the second section, 2. The means, 100, for applying a force on said cylindrical sidewall, 16, extends around the outer circumference of the sidewall, 16, as shown in Figure IA.

[53] An example of means 100 for applying a force on the cylindrical sidewall 16 of the plug is shown in rigures 1AIC and 2 In the example shown, this is an element that changes shape on heating; for example a shape memory alloy actuator may be used. In the examples shown in these figures, the shape memory alloy actuator is a shape-memory alloy wire extending around the outer crcurnfere'ice of the sidewall 18 aria, in particular around he crcumferertial line of wcakness, or predefined fracture plane 90 The shape memory dlloy wire may be formed from a Nickel Taanium alloy such as Nibnol I M uI may also be formed from other shape memory aUoy material known in the art, The shape memory afloy wire, when activated, changes s ape ani exoancs in diameter In some examples the shape memory alloy wire is activated by increasing the temperature of the alloy.

For example, the shape memory alloy wire may be connected to an electricai power supply in order to be actuated through electrical joule heating. An example of an electrical power supply could be a constant current supply or a current limited DC supply, 154] In the example shown in Figure IA, the shape memory alloy wire 100 extends around the urcumforenco of the sidewall 16 and is posi onod so as to be in the same pane as the predefined fracture plane 90. The shape memory alloy wire is maintained in a position arounc the circumference of the sidewall 16 aich tht movement and conton of the wire is constrained In one example, the shape memory alloy wire 103 is crimDed by a crimp connector lOb n order o secure the shape memory alloy wire 100 in position around the circumference of the sidewall 16. Although the examples show crimp connectors, such as 105, the shape memory alloy wire may be secured by other means, such as welding etc..

[55] The shape memory alloy wire 100 may be pre-strained by 5% to 104 When the shape memory alloy wire 100 is heated above a transformation temperature, by for example electrical joule heating the wire 100 will attempt to recover the strain b contracting in length and expanding in diameter The straul recovery is however constrained by the crimp connectors 105 and a large tocalised tAmes (e q -400MPa) is tius imparted on the circumferential sidewall 16 at all points of contact This stress nitiates bnttle fiacture cus ng section 1 ci the plug to fracure from secton 2 of the plug The wire 100 effeotwely cuts1 througn the circumference of the sidewall 16 of to plug and orovides a clean break, which reduces the number of fi agments sPar fracture As an example a N Ti alloy has a transformation temperature of between -50°C and 95°C However, other alloys, tor example NiTiNb, could aiso be used which have a transformation temperature in.

excess of 110°C 156] As shown in Figures lB and IC, a groove 110 may be formed in the sidewall 16 of the plug. The shape memory alloy wire 100 may be placed in the groove 10 before crimping or wading the groove 110 allows for the snape memory alloy wire 100 to be positioned in the predefined fracture plane 90 and constrains rnovemerr and contraction of the shape memory alloy wire 100 After the shape memory alloy wire 100 has been crimped (or welded) by, for example, cr mp connectors 105, the shape memory alloy wire 100 heated above a transformation temperature, for example as described above.

[57] The plug 10 may be corfigured to have a frangi-ile plane aong which the plug is fractured, when activated, to break the seaL In the examples described the frangible plane can result from a tapered configuration which can result, for example, in a thinner wall portion. The frangible plane could be formed by a top hat configuration such as that described above.

[58] Due to the shape of the frangiDle plug 10, wiere the ouar and inner surface have an abrupt change in their geometric shape, when a pressure is applled by a fluid in a recess in the frangible pkg IC, a stress can be created on the surfaces of 6 the plug 10 and the strass is conenrated in a predetermined plane The seal may be broken by providing a force at the predetermined plane. The fluid can then flow from the inlet port to the outlet port [59 As rentioned above, where the outer and inner surface of the sidewall have an abrupt change n their geometnc shape, and in particular duo to the fact that the part of the bevelled portion on the outer surface of the sidewall that has the smaflest diameter hes generally the same lane as the part of the heielod portion ct the inner surface of the sidewall that has the greatest diameter, when a unform pressure is apphed to the second end 12 of the plug, and in particular. the recess 22, a stress is createc and may be concentrated in a predetermined piane. The uniform pressure, for example by the fluid in the recess 22, applied may result in a plane of principal, or increased stress (relative to the surrounding areas) 90.

[$Q] In this example, the weakened or frangible plane 90 can occur at this location because the thickness of the sidewall of the plug is at its minimum in this plane, due to the relative positions of the bevelled portions present n the outer su"acc of the sidewal 30 and the inner surface of the sidewall of the recess 23 and the r corresponding diameters and circumferences as seen in Figure 16 [61] The intersection of this predefinod plane with the outer surtase of the sidewall of the plug can be seen in Figure 1 D, which shows the principal stress distribution of the plug when a uniform pressure is applied to the second end 12 of the pLug by fluid being present in the recess 22.

[62] This predefined plane 90 may therefore provide a weak area of the plug that intersects both the inner surface 23 (within the recess 22) and the outer surface 16 of the sidewall of the plug, and can be seen, for example, in Figure 1D as a circimferential kne cc weakness 90 extending around the sidewall of the plug Ths predefined plane 90 is therefore referred to herein as a predefired fracture plane, as it predefines the location and form of brittle fracture of the plug.

[63] In other examples, the frangible plane 90 could be formed by a different structure or, for example, by a different material or composition. Of course, the franaible plane 90 need not be present Th the frangible plug.

64] The means 100 for applying a force may be posifloned to extend around the cwcumferenhal hne of wea<ness, or predotermned fraAure plane to assist n breaking the frangible plug. In the example shown in Figure 1A, the shape memory al oy wire s posbored so as to be n the' same plane as the predetneC fracture plane 90.

65] The groove 110 described above could also be Formed in the predefined fracture plane 90 of the plug. The groove 110 therefore extends around the outer cwcumfrence of the sidewall 16 r the predefined fracture plane 90 [66] The provson of a orce to a plug havtng a prodofmod fracture plane therefore may result r a much cleaner reak than to a plug the' does not have suo'i a predefined Fracture plane.

[67] Figure 2 shows an example of a shape memory alloy wire 100. The shape memory alloy wire 100 in this example comprises vo shape memory alloy wires 100' and 100'. Shape memory alloy wire 100' extends around th.e outer cfrcurnference of the sidewall 16 of the plug In a semicircle. Shape memory alloy wre 100" extends around the outer circumference of the sidewall ISo! the plug in a semkcErcle opposUe shape memory alloy wire 100' The shape memory alloy wwes and 100" are conb!ned Ic loin a u'rrle around the plug and are cnmped (or welded) by crimp connectors 105. It s to be noted however that any number of shape memory alloy wires could be used. Also, windings of shape memory alloy wire could also be positioned around the outer circumference of the sidewall 16 [68] Agures 3A and 38 show alternative arrangements for a snape memory alloy As descnbed above, the shape memory alb wres 100' aid 103' may be weded or crimped. However, in the arranqements shown in Figures 3A and 3B, there is no need for welding or crimping.

[69] As shown in Figure 3A, the shape memory aHoy 30 may be continuous and, n this example, there is provided a shape memory aro wirc 300 In the example, shown, the wre 300 s provided as a nng shape Of course, other shapes nay be provided to fit circumferentlally around the sidewall 16 of the plug. The shape memory a hy 30 nay also include electrica contacs 310 to oc connected to a powe supply souice, as descnbed above In te example shown in Figure 3k the electrical contacts 310 are situated opposite each other on the shape memory ahoy wire 300 Of course the eloctnc& contacts may be provided any-Athere on the shape memory ahoy wire 300. As mentioned above, the ectricaI contacts 310 are connected to a power supply source such that heat is applied to the shape memory alloy wire 300. The shape memory alloy wire 300 can then expand to cause the plug to fracture.

70] Figure 3B shows a further aiternative configuration to the shape memory alloy 30 as shown in Figure 3k In this exam. the shape memory alloy 31 has shape memory alloy.ne 300 ano eectncal contacts 310, as cescribed above Ii addition, the shape memory alloy 31 has portions 302 that assist in fracturing the pLg I he po'tonc 302 are provided on the shape memory alloy wire 300 and face inwards from the shape memory alloy wire 300. In the example shown in Figure 36, the portions 302 are needle-like protrusions that can rest agains; the sidewall 16 of the plug Wher 1he shape mamory alloy tin-300 is hratcd, the wire 303 expands in diameter and contracts in length, thereby providing a force on the sidewall 16 of the plug. The needle-like protrusions 302 assist in fracturing the plug when the wire is heated, [71] Figures 4A and 46 show further alternative arrangements for a shape memory alloy Figure 4A shoves a siape momoy alloy 40 In the example shown two secondary metal wires 400 and 401 extend around the circumference of the pluc The secondary metal wires 400 and 401 are semi-circular in shape in this example, but may be other shapes. As shown in Figure 4k the shape memory alioys 410 -rinc 411 may be arranged to hold [he secondary metal wires 400 and 41 in p ace around the sicewall i6 of tie plug For example, a first single shape memory alloy wire 40 may be wound around an end of the secondary metal w res 400 anC 401 A second shape memory alloy wire 41 1 may be wouni around opposing ends of the secondary metal wires 400 and 401. The first and second shape memory alloy wires 410 and 411 hold the secondary metal wires 400 and 401 in place around the sidewafi 16 of the frangible plug. Of course, more than one shape memory aHoy wire may be wound around the ends of the secondary metal wires.

72] Electrical contacts 405 are positioned on the secondary metal wires 400 arid 401, as with the shape momory alloy in Figures M and 36 mc electrical contacts 405 may be connected to a power supply to supply heat to the secondary metal wires 400 and 401 The hoat conducts through the secondary metal wires 400 and 401 to the shape memory alloy wires 41 C and 411 wh oh causes expansion of the shape memory alloy wires 410 and 411 As the shape memory alloy wires 410 and 411 expand, the secondary metal wires 400 and 401 are drawn together and provide a force against the sidewa 16 of the plug causing the plug to fracture.

[73] Figure 46 shows a further alternative configuration to the shape memory alloy 30 as shown in Figure 4A n this example, the secondary meal wires 400 and 401 are held in position around the sidewall 16 of the plug with shape memory alloy wires 410 and 411. The secondary metal wires 400 and 401 may also include eleotcical conf.acts 405, as described above. In addition, the secondary metal wires 400 and 401 may have portions 402 li-at assist in "ractunng the plug The portions 402 may be provided on the secondary metal wires 400 and 401, and face inwards from the secondary metal wires 400 and 401 01 ecu se, the portions 402 may be soparate from the secondary me& wires and may be supported, or held in placs by the secondary metal wires 400 and 401 The portions 402 may be mace from either a metallic or a nonmetallic material When the shape memory alloy is activated, the secondary metal wires 400 and 401 may provide a force to the portions 402 to assist in fracturing the plug. in the example shown in Figure 46, the portions 402 are needle-like protrusions that can rest against the sidell 16 of the pLg When the shaoe memory alloy wires 410 and 411 are heatea the wres 410 and 411 expand, causing the secondary metal wires 400 and 401 to be drawn together such that a force may be provided on the sidewall 16 of the plug. The needle-like protrusions 3u2 assis in fracturing the plug when the shape memory alloy wires 410 and 411 are heated. As an example, the secondary metal wires 400 and 401 of Figures 4A and 46 may be made from steel Howeer, any other suitable electrical conductor could be used.

[74] Figures 5A and 56 show a valve mechanism 5 that comprises a valve body 50, havthg an inlet port 52 and an outlet port 54, and a passageway 56 extendhig therebetween. A frangible plug 10, as described in conjunction with Figures 1 A-I C, is hSd within the valve body 50 to block the passageway 56 between the inlet and outlet ports, and prevent fluid from flowing from the inlet port 52 to the outlet port 54 when the plug is intact.

[15J T-e frangble plug 10, as descr bed in Figures IAA C has a first sLrtace 14 a doscnbed above The first surface 11, in use, sin flow communication wth the outlet oo'i 54 The plug 10, as rnetione above, has an opposing second end 12, which is at the inlet port side of the valve mechanism and which has a second sLrface, w-'ich in use, s in flow communication with tie in at por h2 (761 In some examples, tie outer circumferential surface of the sidewa 16 of dt least a portion of the plug may contact the inner wall of the valve body itself, or may be held by some other means within the valve body and may further comprise a seal between the outer circumference of the sidewaD of the plug and/or between the second end of the plug and/or the sidewalls of the recess within the plug, [77] This in combination with the fact that the first end of the plug is dosed, provides a seal between the inlet and outlet ports of the valve body, which therefore closes the passageway between the inlet 52 and outlet 54 ports when the plug is intact.

[78] The plug 10 a held within the valve body so that a portion o the outer surface of the plug is sea ed to an inner surface of the valve body, as mentioned above This may be achieved by br7ir'g the cc arnic to th6 valve body v an intermediary low expansion metal alloy. This provides a hermetic seal between the ceramic and the vve body. An example of an intermediary low expansion metal aVoy is a Kovar TM joint. Other seating means may also be used -for example an fran Nickel Cobalt alloy with 29% Nickel and 17% Cobalt.

[79] As a further example, the side wall, 16, of the plug provides two sectionS, 1.

2, one either side of the shape memory alloy 100, as shown in Figure 16. The seal between the valve body 50 is provided in only one of these sections, i.e. the second section, 2, as shown in Figure lB. This is the secflon of the plug that s on the mM port side of the predefined fracture plane, which comprises the bevelled porUon 15 of the outer surface, as we as the portion 19 of the outer surface that is at the second end 12 of the plug, that has a uniform diameter which is greater thai the diameter of the first end 14 of the plug,te. the brim of the top hat shape). The second section also comprises tne portion 24 of the recess 22 which is of uniform diameter and extends from the second end of the plug up to the point at which the inner surface of the sidewaH is bovoUod (we Figure 1 B) 160] Upon applicdflon of an impact force to he plug, for example by using he shape memory alloy elerrent I 00, as described above fracture of the plug therefore occurs across the sktew&l 16 and the first section, 1 of the plug that lies on the side of the shape memory allow 100 that is not sealed to the inner waDs of the valve body 50 and which, in this example, has a smafler outer diameter than the remainder of the plug, breaks away. The second section 2 of the plug that comprises the seal to the inner surface of the val body generally stays intact.

Th s therefore provides a clear open aperture at a predetined position within the plug.

[61] Due to the creation of this clear aperture, the passageway between the inlet and out at ports s opened up so hat a substanLe contained in the recess can be dlsclarged through the outlet port [82] 1 he valve mechanism described above is therefore a s ngleLse, cr repairable, valve mechanism that provides significant advantages over previous valve mechanisms, as when operated, it is able to create a clear opening between the inlet 52 and outlet 54 ports of the valve due to the fact that the plug cuts through a sidewall using shape memory alloy. 30'

183] In the example where there is provided a predefined fracture plane 90, the prodetinod f'a.ture plane 90 lies generally perpendicular o the direction of the low direction and so the resistance of the frangible plug to bursting or fracture due to applied presswe on tie side nf the inlet port 52 is maximised i7 184] This valve mechanism also aflows for the minimisation of the number of components and the complexity of the va've design, thereby reducing cost of the valve mechanism t further retans the rapid opemnq and free flow chardrterlncs of known devices and methods, whst removing the need for pyrotechnic cartridges and prodkig herrniticity where required.

[85] The frangthle plug may be formed from a brittle material for example a britfie ceramic, vitreous or polymeric material. For an alumina ceramic disc, the matertaL may compiso a 96% dense A umira A 203 ceramc [8$] These new typos of seals provide significant advantages over known valve mechanisms as they provde herrniUcity whilst also minimising the number of components and coriplexity of the valve design and therefore reducing the cost aid providing higher reliability.