GAS GENERATING DEVICES

Abstract: A gas generating device which comprises a container (1) within which is sealed a gas generator in the form of a water-reactive substance (14, 11) and means are provided to break the seal (5, 6) in situ and allow water to penetrate the container and react with the substance (14, 11) to produce the gas.

Description: This invention relates to a gas generating device which incorporates a water-reactive gas generating substance. Such devices are well-known and comprise a container within which is stored said water-reactive gas generating substance and which has a closure member which is in sealing water-tight engagement with an opening and is operable by trigger means to break said sealing engagement and admit water to the container through said opening. A device of this kind is disclosed in GB-2165532-A in which a valve controls the admission of water to the container, and in US-3930804 in which a cap is ruptured by an explosive charge to admit water to the container. An object of the present invention is to provide a gas generating device of improved performance. Disclosure of the Invention According to the present invention a gas generating device is characterised in that the container has a closure member which is in sealing water-tight engagement with an opening and is operable by trigger means to break said sealing engagement and admit water to the container through said opening to react with a water-reactive gas generating substance stored therein, characterised in that the container has a pair of opposed walls each formed with an opening, a pair of closure members are provided each in sealing water-tight engagement with a respective one of the openings and each movable to break said sealing engagement, a rod extends between and is movable with the closure members, and the trigger means operates by moving the rod so that the sealing engagement of the closure members with their respective openings is broken substantially simultaneously to allow water to penetrate the container through the openings and react with said substance to produce the gas that escapes from the container. It is also preferred for the closure members, once they have been displaced, to be incapable of resealing the container due to, for example, water pressure causing their return to their original position in the container wall. This can be achieved by means of a lock spring which is attached to the closure member and which, in a sealing position, is elastically deformed against a relevant part of the container or an extension thereof but, on removal of the seal, springs to its natural shape and thereby prevents the seal being re-seated in its sealing position. The gas generator may be any water-reactive substance which produces a gas when in contact with water. Usually, copious amounts of gas are required and hydrides are preferred as a general class of useful substances, producing hydrogen gas in contact with water. In general any suitable hydride could be used including those of lithium, sodium, potassium, aluminium, calcium and magnesium and also mixed hydrides, especially those containing aluminium. Lithium hydride or lithium aluminium hydride are preferred in the present invention. The devices of the invention are capable of having a long shelf life and, once operated, of allowing an instantaneous ingress of water to the interior of the container. Thereafter, however, the rate of evolution of gas can be varied in a predetermined manner. For example, there is a wide choice of gas generators per se and, in addition, the physical characteristics of any particular gas generator, such as its extent of compaction or density per unit volume, may be varied from device to device or even varied within different regions of a single device. Equally, inhibitors or accelerators may be added to the gas generator to determine the rate at which water comes into contact with the generator and/or the rate of reaction once it does come into contact. In a preferred embodiment to cause a fast rate of gas generation, the canister contains a generator comprising substantially pure lithium hydride or lithium aluminium hydride granules. In a preferred embodiment to cause a slower rate of gas generation, the canister contains a generator comprising substantially pure lithium hydride or lithium aluminium hydride granules admixed with a filler material such as wax, for example paraffin wax, water soluble salts, for example sodium chloride, greases, oils and soft rubbers, for example butyl rubber or mixtures thereof. The generator may also optionally contain either aluminium particles or a lithium-aluminium alloy in granular form, for example one containing 20% lithium and 80% aluminium by weight, to moderate the reactivity of the generator with water. A generator which has been found to be particularly useful contains lithium hydride granules, paraffin wax and a lithium-aluminium alloy, for example 50% lithium hydride granules, 40% paraffin wax and 10% lithium-aluminium alloy (20%/80%) in granular form, all by weight. In certain cases it may be important to ensure that the gas generator (whether it is one to cause a fast rate of gas generation or a slow rate of gas generation) produces gas in a controllable, uniform manner. In such cases in particular, it is preferred that the generator itself does not comprise a single charge of gas generating substance but rather comprises a number of individual components arranged so that, in use, water can penetrate between the components and consume the components simultaneously. Most preferably, means are provided in such generators to hold the individual components in a predetermined manner relative to each other so that during consumption they do not move within the canister holding the generator. This can be achieved by packing the generator components in layers and separating the layers by water permeable barriers, for example sheets (or whatever) of mesh. The use of individual components for the generator, especially separated by water permeable barriers so that they cannot move within the canister, also allows water penetrating the canister to contact the entire surface of each component. This can be important not only in achieving uniform gas generation in general but also in controlling the temperature throughout the generator. The rate of gas evolution generally depends on the surface area of gas generator substance exposed to water in use. To obtain a substantially constant rate of evolution, it is therefore important to ensure that this area remains constant. This is preferably achieved in the invention by masking part of the generator substance with a water impervious outer layer; for example, in the case of a cylindrical generator (or a series of cylindrical components) the curved circumferential surface may be masked whilst leaving one or both flat ends unmasked and exposed to the water. Generators providing a varied rate of gas generation can also be used in the devices of the invention. This can be achieved by having a generator with two or more individual "charges" of different compositions which, in use, can be consumed by water entering the device at different rates either simultaneously or consecutively. For example, the canister may contain an outer shell of a first generator composition within which is contained a second composition. In the case of a cylindrical canister having sealing discs in the centre of each end, the outer shell may also be cylindrical so that water entering the canister first encounters the generator composition positioned within the inner shell; if that inner composition is more reactive with water than the outer composition, then the inner generator clearly will be consumed first. Furthermore, physical barriers may be used to ensure consumption of the first generator composition before the second (or subsequent) compositions contact the water. This can be achieved by partially wrapping one or more of the individual compositions with, for example, a heat shrinkable plastic material or metal foil. With regard to the gas generator substance, it is important (except in the case of a single component system) that the ingredients are well mixed to ensure a uniform distribution throughout the substance; this applies particularly to the hydride or other gas generating ingredient. The grain size of the ingredients, particularly of the gas generating ingredient such as lithium hydride, is important in that it affects the rate of consumption of the substances by the water. Generally, it has been found that the smaller the grain size, the greater is the rate of consumption. Lithium hydride is a preferred gas generating ingredient (or substance in its own right) and, with a grain size of, say, 30 mesh can be pressed to form a pellet. Mixtures of lithium hydride, paraffin wax and a lithium-aluminium alloy, in particular the specific one referred to above, can also be relatively ready pressed to form a pellet. Because of the nature of the materials, i.e. their reactivity with water in particular, it is essential for all the processing to be carried out in dry conditions, preferably in the presence of a purging inert gas atmosphere such as argon to prevent contamination during mixing. If wax or similar substance is present, the mixing temperature should be above its melting point (but not at the boiling point). Thereafter pressing of the mixed substance should also be effected in dry conditions and again preferably in the presence of an inert gas. The pressing pressure can be important. If it is too low, the pressed pellets tend to fragment and break, causing erratic performance and short life. If it is too high, the resultant compaction can retard the reaction rate with water and it can be difficult to remove the pressed pellets from the mould. Finally, the packing of the generator into the container should also be effected under dry, inert atmosphere conditions. The devices of the invention have many varied uses including buoyancy bags for underwater lifting and salvage purposes, for pressurising inflatable objects underwater or otherwise and emergency gas supplies for balloon inflation, etc. For many of these uses, the generated gas will escape the container via an aperture formed when the sealing disc (or whatever) is removed and this aperture may be suitably fitted with means to direct the gas into a container or other chosen vessel depending on the use to which the gas is to be put. Description of the Drawings For a better understanding of the invention, reference is now made, by way of exemplification only, to the accompanying drawings in which: Figure 1 is a sectional view through a first gas generating device of the invention, Figure 2 is a sectional view through a second device of the invention, Figure 3 is a sectional view through the device of Figure 2 along the line IV - IV. With reference to the drawings, Figure 1 shows a gas generating device comprising a cylindrical container 1 having two end plates 2, 3 bonded thereto and a spool valve having a central thrust rod stem 4; at either end of the stem 4 are rigidly attached discs 5, 6, both of which having an "O" ring contained in an annular groove in its curved surface. The disc 6 seats against the end plate 3 within an external annular flange 9 and covers a series of openings 28 through the end plate. The annular "O" ring around the disc 6 forms a seal with the flange 9. The disc 5 is received within a circular opening 7 in the end plate 2 and is sealed therein by its outer "O" ring. The disc 6 is of larger diameter than the disc 5 so that in use the pressure acting externally on both discs produces a nett axial force on the spool valve which urges the disc 6 against the end plate 3. Additionally, the spool valve is maintained in its assembled position by a lock spring 10 mounted on the stem 4 adjacent the disc 6 so as to cooperate with an aperture 8 in the end plate 3 through which the stem 4 passes. The spring 10 comprises a ring portion placed about the stem 4 and a rectangular portion depending from the ring portion. The rectangular portion normally lies proud of the surface of the stem but in position in the aperture 8 is elastically deformed and thereby grips the end plate 3. When it is desired to trigger the device and generate gas, a bolt 27 is caused to impinge on the outer surface of the disc 5 by explosive (or whatever) means and thereby dislodge the disc 5 from its aperture 7. Disc 6 is simultaneously displaced from its flange 9 by the stem 4, thereby opening apertures 29 also. When this has been effected, the rectangular portion of the lock spring 10 is also displaced from aperture 8 and, because of the elasticity of the spring, does not allow the disc 6 (or therefore disc 5) to re-seal in the aperture. The interior of body 1 contains a gas generator. In the embodiment shown in Figure 1; this comprises an outer cylindrical component 11 having a physical, water impermeable separator 12 on its inner face (and optionally on its outer face) and therefore presenting only one surface 13 to water entering the container; a separate component 14 is contained within the cylinder 11. In use of the device, therefore, water entering through the aperture 7 on removal of the disc 5 will react first with the (normally faster reacting) component 14 and only thereafter with the (normally slower reacting) component 11. By virtue of the presence in this case of the physical separator 12, the component 11 is consumed only slowly because of the limited interface area between the component and the water. With regard to Figures 2 and 3, there is shown a similar type of device to that of Figure 1 with the generator having a plurality of components to provide a varied rate of gas generation. In particular, the device of Figures 2 and 3 possesses, in addition to the parts common to the device of Figure 1, three sets of three individual generator components 18 in the form of cylinders whose diameter approximately equals the internal radius of the container 1. The cylindrical components 18 can therefore be positioned about the stem 4 in the manner shown in Figure 3. Packing of the container 1 with the cylindrical components 18 is achieved by providing a spacer ring 19 on which is placed a water permeable spacer in the form of a mesh disc 20. Three components 18 are then placed in this disc 20 in the manner shown in Figure 3 and further discs 21, 22 and two further sets of three components 18 are added. A final disc 23 and then a disc 24 of gauze are then provided to complete the first "charge" of generator composition. Each cylindrical component 18 is encapsulated in copper foil except for the upper (flat) surface thereof so that, in use, water penetrating through the aperture 7 and passing between the components 18 and the mesh discs 20, 21, 22 and 23 contacts the generator substance only at the exposed upper surface of each cylinder, thereby providing a substantially constant surface area of contact between the generator substance and the water and thus providing a substantially constant rate of gas evolution. The upper volume of the container above the gause disc 24 contains a separate generator "charge" held between the disc 24 and a gauze cylinder 25 positioned about the stem 4. This upper charge 26 will generally provide a greater rate of gas evolution than the first charge and may conveniently comprise pure lithium hydride granules of predetermined grain size. In use, therefore, the generator device shown in Figures 2 and 3 can provide differential rates of gas evolution, the rate of evolution from each charge may of course be varied by one or more of the selection of grain size of the active generator composition in particular, by the compaction pressure and density of the generator, by the presence of waxes and other additives and by encapsulation of one or more surfaces. Furthermore, the generator devices of the invention may possess more than two "charges", i.e. there may be a plurality of separate charges depending on the use to which the devices are to be put.

Claims: A gas generating device comprising a container (1) having a closure member (5) which is in sealing water-tight engagement with an opening (7) and is operable by trigger means (27) to break said sealing engagement and admit water to the Container (1) through said opening (7) to react with a water-reactive gas generating substance (11) stored therein, characterised in that the container (1) has a pair of opposed walls (2, 3) each formed with an opening (7, 28), a pair of closure members (5, 6) are provided each in sealing water-tight engagement with a respective one of the openings (7, 28) and each movable to break said sealing engagement, a rod (4) extends between and is movable with the closure members (5, 6), and the trigger means (27) operates by moving the rod (4) so that the sealing engagement of the closure members (5, 6) with their respective openings (7, 28) is broken substantially simultaneously to allow water to penetrate the container (1) through the openings (7, 28) and react with said substance (11) to produce the gas that escapes from the container. A device as claimed in claim 1 in which the closure members (5, 6) are discs in sealing engagement with walls around circular openings. A device as claimed in claim 2 in which the rod (4) is coaxial with the discs (5, 6). A device as claimed in any one of the preceding claims in which the container (1) is cylindrical with the openings (5, 6) formed in its opposed end walls and the closure assembly (4, 5, 6) coaxial with the cylindrical axis of the container (1). A device as claimed in any one of the preceding claims in which at least one of said closure members (6) engages against a seat (3, 9) around the periphery of a respective opening (28). A device as claimed in any one of the preceding claims in which means (10) is provided to prevent said closure members (5, 6) resealing in water-tight engagement with their respective openings (7, 28) once they have been operated to break said sealing engagement. A device as claimed in claim 6 in which said means (10) comprises spring means that urges at least one closure member (6) into sealing water-tight engagement with its respective opening (28). A device as claimed in claim 7 in which the spring means (10) is forcibly over-ridden when the closure member (6) is operated and then acts to prevent the closure members (5, 6) from being sealingly re-engaged with their respective openings (7, 28). A device as claimed in claim 5 in which the relative areas of the externally exposed surfaces of the closure members (5, 6) are such that in use pressure forces acting externally on the closure assembly (4, 5, 6) balance one another partially and urge said at least one closure member (6) into engagement with said seat (3, 9). A device as claimed in any one of the preceding claims in which the trigger means (27) comprises an explosive-operated bolt. A device as claimed in any one of the preceding claims in which the container (1) contains a first substance (14) that reacts rapidly with water and a second substance (11) that reacts more slowly with water. A device as claimed in claim 11 in which the first substance (14) is stored in toroidal form and has a cylindrical surface (13) that is completely exposed to the water. A device as claimed in claim 11 or 12 in which the second substance (11) comprises a plurality of compressed pellets (18) that are all exposed simultaneously to the water. A device as claimed in claim 13 in which each pellet (18) has a constant cross-sectional area with only an end thereof exposed to the water. A device as claimed in claim 13 or 14 in which the pellets (18) are stored in layers of more than one separated by spacers (20) that allow access of the water to all of the pellets (18).

Inventors: CARTER, ANDREW JOHN, GOODWIN, JOHN CHRISTOPHER, KIRBY, ROY, SIMONS, PHILIP SIDNEY
Applicants: DOWTY MARITIME SYSTEMS LIMITED
Application year: 1988
Main classification: B01J7
IPC codes: B01J7, C01B3