FOREIGN PRIORITY 
       [0001]    This application claims priority to United Kingdom Patent Application No. 1418081.4 filed Oct. 13, 2014, the entire contents of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    A frangible diaphragm for use in a valve mechanism, and, more particularly, a single-use valve mechanism that may be used for discharging fluid is described herein. The frangible diaphragm and valve mechanism may have particular use in the field of suppressant release, such as a fire suppressant fluid. 
         [0003]    The examples described herein relate to devices and methods for the controlled release of a fluid flow substance. They are particularly suited, but not limited, to the controlled release of a suppressing or extinguishing agent from a cylinder. The devices and methods described may further be used for the rapid deployment of an extinguishing agent from a cylinder, such as those that may typically, although not exclusively, be used on moving platforms such as aircrafts, trains, military or commercial vehicles. 
         [0004]    Such valves fall into two main groups; non-hermetic and hermetically sealed. The former category is typified by the high rate discharge (HRD) valves used on suppressors in military and commercial vehicles. These can be electromechanical or protractor fired, consisting of either a flapper or poppet as the main openings mechanism. Both systems contain multiple moving components and rely on O-ring seals for integrity. Such valves can be relatively expensive and require refurbishment prior to use. 
         [0005]    Further applications, such as aerospace, require that the suppressor be hermetically sealed to minimise leakage over the required environmental range and to extend service life. Such hermetically sealed extinguishers use an explosive cartridge located on the outside of an outlet disc or diaphragm, which upon actuation ruptures and releases agent into a distribution network or directly into the protected fire zone. This method, although very fast and reliable, is prone to fragmentation of the diaphragm during actuation and requires the use of pyrotechnic cartridges. These valves require periodic maintenance and replacement and have associated handling, transit and storage restrictions. 
         [0006]    The examples described herein aim to retain the rapid opening and free flow characteristics of the prior art, whilst reducing cost, removing pyrotechnic cartridges and providing the option for hermiticity where required. 
         [0007]    DE 19736247 discloses a component having a body made of brittle material and the use of piezoelectric elements both embedded and laminated into the body such that, when the body is energized by the piezoelectric elements, a portion of the component is destroyed. 
         [0008]    European Patent Application No. 14160040 discloses a ceramic disc with a pre-defined stress plane which is fractured by impact by a point force. Means for braze attachment of the disc, means for minimising fragmentation and a means for retaining the free section of the disc after fracture are also disclosed. 
         [0009]    EP 1582789 describes devices and methods for controlling the release of a substance which are particularly suited to the control of substances such as fire extinguishing media. The devices and methods described comprise a housing having an inlet for connection to a source of a substance and an outlet, with a passage extending therebetween. The passage may be closed by a frangible element which comprises a ceramic disc that is connected to a source of electrical current. The disc may be a metal oxide ceramic disc, and may be fractured by an electrical pulse which is applied to the disc. 
       SUMMARY OF THE INVENTION 
       [0010]    In one example, there is provided a frangible diaphragm for use in a valve mechanism, said frangible diaphragm comprising an actuator substance provided in, or on, the frangible diaphragm, wherein the actuator substance expands from a smaller volume to a larger volume on application of heat such that a force generated by the expansion causes the diaphragm to fracture. 
         [0011]    In one example, the actuator substance may be wax. The wax may be petroleum based or the wax may be a synthetic wax. 
         [0012]    Further, the frangible diaphragm may comprise a heating element for heating the actuator substance. The heating element may be formed from a coil of resistance wire provided on, or in, the actuator substance. 
         [0013]    Further, the frangible diaphragm may comprise one or more discs and the actuator substance may be provided in, or on, at least one of the one or more discs such that, when activated, the actuator substance causes at least one of the one or more discs to fracture. The actuator substance may be located adjacent an outer edge of at least one of the one or more discs. 
         [0014]    The frangible diaphragm may further comprise means for rigidly attaching the one or more discs to each other. The means for rigidly attaching the one or more discs to each other may comprise a locking ring that is configured to be attached to a holder surrounding the one or more discs. 
         [0015]    In another example, 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 frangible diaphragm as described above, wherein the diaphragm is held within the valve body such that the diaphragm blocks the passageway when the diaphragm is intact, and wherein, when the actuator substance is activated, the diaphragm fractures such that fluid can flow from the inlet port to the outlet port. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  shows a view of a frangible diaphragm. 
           [0017]      FIG. 2  shows a view of section A-A of  FIG. 1 . 
           [0018]      FIG. 3  shows a detail view of section B of  FIG. 2 . 
           [0019]      FIG. 4  shows a view of the frangible diaphragm of  FIG. 1 . 
           [0020]      FIG. 5  shows a view of an alternative frangible diaphragm. 
           [0021]      FIG. 6  shows a valve mechanism with the frangible diaphragm of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIGS. 1 and 2  show a frangible diaphragm  10  for use in a valve mechanism is shown. In general, the frangible diaphragm  10  is provided between an inlet port and an outlet port of a valve mechanism (described later). The frangible diaphragm prevents fluid from flowing through the conduit, until it is activated, by forming a seal across the valve between the inlet and outlet port. When the frangible diaphragm is activated, the seal is broken so that fluid can flow through the conduit from the inlet port to the outlet port of the valve mechanism. 
         [0023]    Generally, there is provided an actuator in the frangible diaphragm that expands when heated. The actuator may be embedded in, or formed on, the frangible diaphragm. When the actuator is heated, the expansion of the actuator is constrained thus creating a force causing the diaphragm to break. The seal provided by the diaphragm is therefore broken so that fluid can flow between the inlet port and outlet port of the valve mechanism. 
         [0024]    The actuator in the frangible diaphragm  10  may be an actuator substance, for example, wax. 
         [0025]    An example of a frangible diaphragm is shown in  FIGS. 1-4 . The frangible diaphragm  10  may be in the form of a disc, and in this example comprises a first disc  12  and a second disc  14  In the example where two discs are shown, the two discs allow for a lower force or smaller element to fracture the discs. The fluid pressure within the valve mechanism, against the discs, can cause one, or both, of the discs to fracture. First disc  12  and second disc  14  have an upper surface and a lower surface. The first disc  12  and second disc  14  provide, before activation, a seal that prevents fluid from moving from an upper conduit  17  to a lower conduit  16 . As described later, the upper conduit  17  is in flow communication with an inlet port of the valve mechanism, and the lower conduit  16  is in flow communication with an outlet port of the valve mechanism. The first disc  12  and second disc  14  may be formed from a brittle ceramic material, for example alumina, but may also be formed from any similarly frangible, for example, brittle vitreous or polymeric material. 
         [0026]    As shown in  FIG. 2 , in one example, the upper surface of the second disc  14  is adjacent the lower surface of the first disc  12 . The two discs  12  and  14  act as a seal to prevent fluid from flowing through the conduits  16  and  17 . In order to maintain the position of the discs  12  and  14 , a means for rigidly attaching the second disc  14  to the first disc  12  is included in the frangible diaphragm. In the example shown in  FIG. 2 , the means for rigidly attaching the second disc  14  to the first disc  12  is a holder  11  that includes a screw thread to receive a locking ring  15 . The discs  12  and  14  are placed in the holder  11  and the locking ring  15  is then screw threaded into the holder  11 . A flanged portion  20  acts as a stop within the holder  11  such that the discs  12  and  14  are held in position in the holder  11 . When the locking ring  15  is screw threaded into the holder  11 , the second disc  14  and the first disc  12  are rigidly attached so as to prevent relative movement of the discs  12  and  14 . In one example, the holder is metal, but the holder may also be formed from other suitable materials. Other means for rigidly attaching the discs  12  and  14  together could be used, for example by induction brazing to form a joint between the discs  12  and  14  around their outer diameter. Another example may be to use an adhesive/epoxy bonding on the lower surface of the first disc  12  and on the upper surface of the second disc  14 . 
         [0027]    A hermetic seal may be provided between the holder  11  and the firstdisc  12 . In one example, the holder  11  may be braze attached to the first disc  12 . For example, a hermetic seal may be provided through braze attachment of, for example, a low expansion alloy (i.e., Kovar™) flange to both the first disc  12  and the holder  11 . 
         [0028]    The frangible diaphragm has a disc-shaped surface when forming a seal in a cylindrical valve conduit, but can of course be appropriately shaped to seal any conduit. As an example, the frangible diaphragm  10  of  FIGS. 1-4  is shown to be cylindrical. The discs  12  and  14 , and locking ring  15  are also shown to be cylindrical. However, these components of the frangible diaphragm  10  may be any other suitable shape. 
         [0029]    To break the seal, force is applied from within the diaphragm to fracture the diaphragm. As mentioned above, the force comes from an actuator that may be embedded in or formed on the frangible diaphragm to cause the diaphragm to fracture. In the two disc embodiment shown in  FIGS. 2 and 3 , for example, the actuator could be embedded in or formed on one of the discs causing that disc to rupture, with the other disc fracturing due to stresses applied to it from the fracture of the disc containing the actuator. 
         [0030]    As shown in  FIGS. 2 and 3 , the second disc  14  includes means  100  for applying a force to the second disc  14 . The means for applying a force, when activated, causes the second disc  14  to fracture. The first disc  12  then fractures due to the increased stress applied as a result of the other disc fracturing, for example, from the fluid in the upper fluid conduit  17  to allow fluid to flow through both the upper conduit  17  to the lower conduit  16  (i.e., from an inlet port to an outlet port of the valve mechanism). In the example shown in  FIG. 2 , the means  100  for applying a force to the diaphragm includes an actuator substance  102  capable of expansion. In this particular example, the actuator substance is embedded in or located in a void (not shown) in the second disc  14 . In other examples, the actuator substance could be in the first disc  12  or both discs  12  and  14  or the diaphragm may comprise only a single disc or more than two discs. 
         [0031]    For activation, some means are provided to heat the actuator substance. In this example, a heating element  103  is attached to or embedded in the actuator substance. The heating element  103  is connected to, for example, an electrical power supply such that heat can be applied to the wax actuator  102 . In some examples, the electrical power supply could be a constant current power supply or a current limited DC power supply. The heat from the heating element  103  causes the actuator substance  102  to expand. In one example, the expansion of the actuator substance  102  occurs due to a change of state of the actuator substance when applied with heat. For example, the actuator substance  102  could move from a solid state to a liquid state, when heated. In an example, the heating element  103  may be formed from a coil of resistance wire. As an example, where the actuator substance is 5 mm in diameter and 1 mm long, 12 J would be required to bring the actuator substance to a melting temperature, for example 100 Celsius. 
         [0032]    As the actuator substance  102  expands. it delivers stress to the disc in which it is provided—here, the second disc  14 , for example. This exerts a force on to the second disc  14  such that the second disc  14  fractures. In some examples, the actuator substance  102  expands by between 10%-20%. As the actuator substance  102  is constrained by its location in the disc—here, being provided in a void in the second disc  14 , it is unable to expand and so a stress is applied to the second disc  14 . As an example, this may be a force of between 200 MPa and 400 MPa. The stress applied to the second disc  14  causes the second disc  14  to fracture. In the examples shown, the wax actuator  102  and heating element  103  are located adjacent to the outer edge of the second disc  14  to ensure that the fracture propagates around the circumference of the disc to form a clear open aperture. 
         [0033]    The surfaces of the first and second disc  12  and  14  may be sufficiently smooth so as to provide a liquid tight seal to prevent leakage of the actuator substance  102  when, for example, it is in a liquid state. Alternatively, an additional seal may be positioned between the first disc  12  and the second disc  14  to prevent leakage of the actuator substance  102 . For example, a thin metallic (e.g. copper) film may be incorporated between the first disc  12  and the second disc  14 . 
         [0034]    In the example shown in  FIGS. 2 and 3 , the actuator substance  102  and the heating element  103  are connected to an electrical power supply by leads  101 . The leads  101  extend through the second disc  14  and through the lower conduit  16  to an electrical power supply (not shown). A liquid tight seal may be formed between the leads  101  and the second disc  14 . This liquid tight seal may be formed by a suitable metal to ceramic bond, for example, braze attachment or a suitable ceramic epoxy. 
         [0035]    As mentioned above, when the actuator substance  102  is heated, the disc in which it is embedded—here, the second disc  14 , fractures. The fluid contained in the upper conduit  17  is in fluid communication with the first disc  12 . This applies additional stress to the first disc  12 . The first disc  12  is fractured from the pressure applied to the upper surface of the first disc  12  by the fluid contained in the upper conduit  17 . As the first disc  12  fractures, this allows for fluid communication between the upper conduit  17  and lower conduit  16 , thereby allowing the extinguishing fluid to flow from the inlet port to the outlet port of the valve mechanism. 
         [0036]    The first disc  12  may be made of a weaker material than the second disc  14  making it break under the pressure of the fluid once the second disc  14  has been broken. Alternatively, both discs could be made of the same material but break under the force of the fluid when the overall thickness has been reduced by breakage of the second disc  14 . 
         [0037]    The fact that the discs,  12  and  14 , are constrained together, for example by holder  11 , also means that the force that fractures the second disc  14  will act to some extent on the first disc  12 . 
         [0038]    The actuator substance  102  may be a wax, but other suitable materials may also be used. For example, the actuator substance  102  could be a petroleum based wax (e.g. paraffin or microcrystalline), a synthetic polymer wax (e.g. ethylenic polymers, chlorinated naphthalenes), natural animal or vegetable wax (e.g. beeswax, carnauba). 
         [0039]    Although a two-disc arrangement has been described, it is envisaged that one disc or more than two discs could be provided to form a seal between an inlet port and outlet port. One or more discs may have an actuator substance, as described above, to fracture one or more discs. 
         [0040]      FIG. 5  shows an alternative to the arrangement shown in  FIGS. 2 and 3 . In this example, the frangible diaphragm  10  comprises three discs  212 ,  213  and  214 . The three discs  212 ,  213  and  214  each have an upper and a lower surface. The first disc  212 , second disc  213  and third disc  214  provide, before activation, a seal that prevents fluid from moving from an upper conduit  217  to a lower conduit  216 . The upper surface of the first disc  212  is in fluid communication with the fluid contained in the upper conduit  217  and the third disc is in fluid communication with the lower conduit  216 . 
         [0041]    As with the example shown in  FIGS. 2 and 3 , the first disc  212 , second disc  213  and third disc  214  can be rigidly attached by a holder  11 , as described above. The holder  11 , and locking ring  15  rigidly attach the discs  212 ,  213  and  214  to prevent relative movement of the discs  212 ,  213  and  214 . Other means for rigidly attaching the discs  212 ,  213  and  214  could be used, as described above. 
         [0042]    As above, the frangible diaphragm has a disc-shaped surface when forming a seal in a cylindrical valve conduit, but, of course, can be appropriately shaped to seal any conduit. 
         [0043]    In the example shown in  FIG. 5 , the second disc  213  and third disc  214  include means  201  and  202  for applying a force to the second disc  213  and third disc  214 , respectively. The means  201  and  202  for applying a force, when activated, can cause the second disc  213  and third disc  214  to fracture. The first disc  212  then fractures due to the force applied as a result of the other discs fracturing, for example, from the fluid in the upper conduit  217 . As with the example shown in  FIGS. 2 and 3 , the means  201  and  202  for applying a force to the second disc  213  and third disc  214  includes an actuator substance. As can be seen in  FIG. 5 , the actuator substance  202  is embedded in, or located in, a void in the second disc  213  and the actuator substance  201  is embedded in, or located in, a void in the third disc  214 . 
         [0044]    For activation, some means are provided to heat the actuator substances  201  and  202 , as described above in relation to  FIGS. 2 and 3 . When heat is provided, the actuator substances expand and deliver stress to the discs in which they are provided—here, the second disc  213  and third disc  214 . This exerts a force on the second disc  213  and third disc  214  such that the second disc  213  and third disc  214  fracture in a similar way to the two-disc arrangement described above in relation to  FIGS. 2 and 3 . This allows for the first disc  212  to fracture from pressure applied by the fluid contained in the upper conduit  217 . Of course, an actuator substance could also be present in the first disc  212  of the frangible diaphragm, or could only be present in one of the discs  212 ,  213  or  214 . 
         [0045]    As above, the first disc  212  may be made of a weaker material than the second and third discs  213  and  214  making it break under the pressure of the fluid once the second and third discs  213  and  214  have been broken. Alternatively, all three discs could be made of the same material but break under the force of the fluid when the overall thickness has been reduced by breakage of the second and third discs  213  and  214 . 
         [0046]    A valve mechanism  500  including the frangible diaphragm  10  is shown in  FIG. 6 . The valve mechanism  500  includes a valve body having an inlet port  52  and an outlet port  54 , and a passageway  56  extending therebetween. The frangible diaphragm  10  is positioned in the valve mechanism  500  to provide a seal between the inlet port  52  and the outlet port  54 . The upper conduit  17  of the frangible diaphragm  10  (as shown in  FIGS. 1-3 ) is in fluid communication with the inlet port  52 . The lower conduit  16  of the frangible diaphragm  10  is in fluid communication with the outlet port  54 . When the frangible diaphragm is activated, as discussed above, the seal is broken to provide a fluid flow from the inlet port  52 , through the lower and upper conduits of the frangible diaphragm, to the outlet port  54  for deployment of an extinguishing agent. 
         [0047]    The valve mechanism  500  described above is therefore a single-use, or 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 port  52  and the outlet port  54  of the valve due to the fact that the frangible diaphragm  10  provides a clear open aperture using an actuator substance  102 . 
         [0048]    This valve mechanism also allows for the minimisation of the number of components and the complexity of the valve design, thereby reducing cost of the valve mechanism. It further retains the rapid opening and free flow characteristics of known devices and methods, whilst removing the need for pyrotechnic cartridges and providing the option for hermiticity where required.
A frangible diaphragm for use in a valve mechanism, said frangible diaphragm including an actuator substance provided in, or on, the frangible diaphragm, wherein the actuator substance expands from a smaller volume to a larger volume on application of heat such that a force generated by the expansion causes the diaphragm to fracture.