FIELD OF THE INVENTION

[0001] The present invention relates generally to fire fighting apparatus, and more particularly to systems and devices for mixing fire retardant gels with water. The invention is especially suited to the protection of a crew cabin of a fire fighting vehicle, and it will be convenient to describe the invention in relation to that example application. It should be understood however that the invention is capable of broader application and use.

BACKGROUND TO THE INVENTION

[0002] Fire fighting trucks of the type used by Country Fire Authorities are often equipped with a plurality of water sprays which are arranged to shower the truck with water in the event that the fire fighting crew becomes trapped in a fire situation without any escape route. In this situation the crew can take shelter within the truck cabin and deploy the spray system, to hopefully protect the themselves against the surrounding fire attack.

[0003] One limitation with such spray systems is the volume of water that can be carried by the fire fighting truck. For example, during a typical emergency situation in which the crew are sheltered within the truck cabin with the sprays operating, the volume of water required to protect themselves may be at least 600 to 750 litres. This volume of course depends on the extent of the fire threat and period over which occurs.

[0004] A particular difficulty for small fire fighting vehicles, such as a 1 tonne light duty utility vehicle, is that such a vehicle simply cannot carry sufficient water. The typical total volume of water carried by light duty utility vehicle may be merely around 500 litres, so a much smaller volume is then available for emergency crew protection. These vehicles thus carry addition risk when entering fire fighting situations.

[0005] Fire retardant gels are known in the art to have greater effectiveness in suppressing fire than water alone. Such gels are typically sold in the form of a gel concentrate which is then hydrated with water prior to being sprayed on a surface to be protected. One example of such a product is sold under the name Barricade®. This product contains super- absorbent polymers that can withstand high temperatures to protect coated surfaces from fire.

[0006] The Barricade® product is often sold as a "home kit" including a 4 litre container of the concentrate together with a dispensing nozzle on the container which can be connected to a domestic water hose. The dispensing nozzle contains a venturi configuration which creates a vacuum to draw the Barricade® gel from the container and mix it with the flow of water at the point of discharge.

[0007] However, there is a problem using Barricade® fire retardant gel (and similar gels) that makes its use problematic in automatic spray delivery systems such as those installed on fire fighting vehicles.

[0008] In particular, if the gel is left standing for a period of time the components separate so as to form layers or lumps in the container. It must therefore be mixed (such as by shaking the container when provided in a home kit) prior to being dispensed.

SUMMARY OF THE INVENTION

[0009] With the foregoing problem in mind, one aspect of the present invention provides a system for delivering a fire retardant gel mixture, including:

a gel tank;

a gel pump arranged to draw gel from the gel tank;

a ring main connected to an outlet of the gel pump and being arranged to provide a return path for recirculating gel to the gel tank;

at least one branch pipe extending from the ring main;

a gel delivery valve arranged to control gel flow from the ring main to the branch pipe;

a mixing valve having a first inlet port configured to receive gel from the branch pipe and a second inlet port for receiving water, the mixing valve being configured to mix the gel with the water prior to discharge at an outlet port; and

a spray nozzle connected to the outlet port of the mixing valve for distributing the fire retardant gel/water mixture.

[0010] Such a system allows the gel to be recirculated via the ring main to the gel tank, either continuously or periodically, to keep the gel emulsified and thereby prevent it separating or becoming lumpy.

[0011] The system also includes a mixing valve which injects the gel into the water flow prior to discharge at its outlet port. In a typical installation, a spray nozzle would be connected directly or in close proximity to the outlet port of the mixing valve to thereby distribute the gel/water mixture immediately. Such an installation thus addresses a potential additional problem associated with using fire retardant gels in automated delivery systems.

[0012] In an embodiment of the system, a gel return valve is located in the return path of the ring main and a control system is configured to close the gel return valve when the gel delivery valve to the branch pipe is open. This has the effect of directing all gel towards the mixing valve, and spray nozzle, when required.

[0013] Conversely, the control system may open the gel return valve when the gel delivery valve to the branch pipe is closed, thereby recirculating all of the gel back to the gel tank.

[0014] In one embodiment, the system includes a telescopic section extending between the mixing valve and spray nozzle. In this embodiment the telescopic section may be spring biased to a retracted position and be driven to an extended position when water, or a gel/water mixture, is delivered by the mixing valve. In a typical installation of the system on a light duty utility vehicle, the spray nozzles may extend from the periphery of the vehicle so as to be in a position where they can spray the vehicle with the gel/water mixture most effectively. Prior to deployment of the system in an emergency situation, the spray nozzles would be retracted so as to lie substantially within the periphery of the vehicle outline.

[0015] The system of the present invention may be fitted to an existing fire fighting vehicle which already has a water tank and water pump installed. Alternatively, a complete system may be provided as a kit which is intended to be fitted to a standard light duty utility vehicle. Such a complete system would include a water tank and a water pump for drawing water from the water tank and delivering it to the mixing valve.

[0016] In one embodiment, the system is configured such that, in use, the gel pump delivers gel to the mixing valve at a pressure which is higher than the pressure at which the water pump delivers water to the mixing valve. Such a configuration ensures that the gel is injected into the water rather than the water being injected into the gel.

[0017] In one embodiment, the system is configured to provide fire protection for a vehicle cabin by means of a plurality of spray nozzles distributed about the vehicle. In such a system a plurality of branch pipes may be connected to the ring main. For example, a light duty utility vehicle may include 10 branch pipes connected to a ring main, and the ring main may extend substantially around the entire chassis of the vehicle. A corresponding plurality of gel delivery valves are also provided, which each gel delivery valve being arranged to control gel flow from the ring main to the respective branch pipe. Each branch pipe then includes a mixing valve having its first inlet port configured to receive gel from the branch pipe and a second inlet port for receiving water. Each mixing valve is configured to mix the gel with the water prior to discharge at its outlet port. A corresponding plurality of spray nozzles are provided, with each spray nozzle being connected to the outlet port of the respective mixing valve. Collectively, the 10 spray nozzles may be arranged to distribute the fire retardant gel/water mixture substantially uniformly over the entire vehicle cabin.

[0018] In another embodiment, the system may be configured to deliver a fire retardant gel/water mixture to a location distant from the vehicle upon which the system is fitted. In this embodiment, the system may include a spray nozzle directed away from the vehicle. In addition, such a system may include a flexible hose connected between the outlet port of the mixing valve and an inlet of the spray nozzle. With this arrangement the spray nozzle can be directed by fire fighting personnel at a desired target separate from the vehicle, such as the ground ahead of the vehicle, or to provide a fire break alongside the direction of travel of the vehicle.

[0019] The mixing valve may be configured to mix the gel and water in a predetermined ratio, as required for the particular gel being used. For example, the Barricade® fire retardant gel mentioned earlier should preferably be mixed at a ratio of about 5% gel to water.

[0020] Another aspect of the invention provides a mixing valve for injecting a fire retardant gel into a flow of water. The mixing valve includes a valve body defining a first chamber and a second chamber, with the chambers being separated by an internal divider having an orifice which allows fluid to flow between the chambers. The first chamber has a first inlet port for receiving fire retardant gel under pressure from an external source and is otherwise sealed such that the gel is discharged from the first chamber into the second chamber via the orifice. The second chamber has a second inlet port for receiving water under pressure from an external source and has an outlet port which discharges the water from the second chamber in accordance with the pressure of the water source. The mixing valve further includes a movable valve element located within the first chamber and being biased to a closed position in which an operative surface of the valve element seals the orifice to thereby prevent fluid flow between the chambers. In use, the valve element is movable away from the closed position when gel is delivered to the first chamber with sufficient pressure to overcome the bias, thereby allowing the gel to flow through the orifice into the second chamber when the gel pressure is higher than the water pressure. This allows the gel to mix with the water prior to being discharged from the outlet port.

[0021 ] It will be appreciated that, in this mixing valve, the water delivered to the second chamber is discharged at its outlet port with a pressure corresponding substantially to the pressure of the water source. In contrast, the fire retardant gel is injected into the flow of water, via the orifice between the chambers, when the pressure of the gel supplied to the first chamber is, firstly, sufficient to overcome the bias force applied to the movable valve element and, secondly, higher than the water pressure. With the first of these considerations in mind, the bias force applied by the movable valve element is advantageously selected such that the orifice is opened only when the gel pressure is higher than the water pressure.

[0022] In one embodiment, the first chamber has a cylindrical internal bore and the divider forms an end wall of the cylindrical bore. The movable valve element preferably includes an elongated shaft extending longitudinally within the cylindrical bore and it may have a laterally extending actuating surface which, at an outer periphery, is sealed against an internal surface of the cylindrical bore. This arrangement forms a slidable piston which contains the pressurised gel within the cylindrical bore of the first chamber. A spring may be positioned to bias the slidable piston towards the end wall of the cylindrical bore and thereby cause the operative surface of the movable valve element to seal the orifice.

[0023] In a preferred embodiment, the shaft of the movable valve element includes a conical end portion. In this embodiment the conical end portion of the shaft forms the operative surface of the valve element, and it is preferably shaped to extend into and seal a correspondingly shaped orifice when the shaft is in the closed position.

[0024] Alternatively, the operative surface (that it, the sealing surface) of the movable valve element could take a different form and may for example be rounded, square, or any other shape, as long as it can seal the orifice between the first and second chambers. In addition, the first chamber need not necessarily have a cylindrical internal bore; it could instead take any other desired shape, as long as it can be sealed to contain the gel pressure. Also, the movable valve element need not necessarily be in the form of an elongated shaft; it could have any other shape, as long as its structure allows it to be biased to a closed position in which its operative surface seals the orifice and it can be urged away from the closed position when gel is delivered to the first chamber with sufficient pressure to overcome the bias.

[0025] In a further embodiment, the spring which biases the shaft towards the closed position is a coil spring positioned to press against a rear surface, opposite the actuating surface, of the slidable piston. It will be appreciated however that any other type of spring could alternatively be used.

[0026] In one embodiment, the mixing valve includes a spray nozzle connected directly or indirectly to its outlet port. In a further embodiment, a telescopic section may extend between the mixing valve and the spray nozzle. In this embodiment, the telescopic section may be biased to a retracted position and it may be driven to an extended position when water or gel/water mixture is delivered to the mixing valve. [0027] A further aspect of the invention provides a system for delivering a fire retardant gel mixture, including:

a gel tank;

a gel pump arranged to draw gel from the gel tank;

a ring main connected to an outlet of the gel pump and being arranged to provide a return path for recirculating gel to the gel tank;

a mixing valve fluidly connected within the ring main and including:

a first inlet port arranged to receive gel from the ring main; a first outlet port arranged to return gel to the ring main;

a second inlet port for receiving water from a water source; a second outlet port for discharging a gel/water mixture; and a movable valve element which is selectively controllable between (i) a closed position in which the gel is not mixed with the water and is instead returned to the ring main via the first outlet port, and (ii) an open position in which the gel is not returned to the ring main and is instead injected into the water and then discharged at the second outlet port; and

at least one spray nozzle connected to the second outlet port of the mixing valve for distributing the fire retardant gel/water mixture.

[0028] Such a system allows the gel to be recirculated via the ring main to the gel tank, either continuously or periodically, to keep the gel emulsified and thereby prevent it separating or becoming lumpy. The system of the invention thus addresses the identified problem associated with using fire retardant gels in automated delivery systems.

[0029] In one embodiment, this system includes an electrically controlled mechanical actuator connected to the movable valve element. The actuator is preferably controllable so as to selectively move the valve element to the open or closed position. In this way, the gel may be injected into a water stream or it may alternatively be recirculated back to the gel tank.

[0030] In one embodiment, the spray nozzle includes a telescopic section which is spring biased to a retracted position and is driven to an extended position when water or gel/water mixture is delivered by the mixing valve.

[0031] In one embodiment, the system is configured to provide fire protection for a vehicle cabin by means of a plurality of spray nozzles distributed about the vehicle. In this embodiment the system includes a distribution manifold fluidly connected to the second outlet port of the mixing valve and a plurality of spray nozzles fluidly connected to the distribution manifold. With suitable positioning of the spray nozzles, this arrangement enables a substantially even distribution of the fire retardant gel/water mixture over the entire vehicle cabin.

[0032] Other preferred features of the system may be as outlined previously in relation to the first system described above.

[0033] A further aspect of the invention provides a mixing valve for injecting a fire retardant gel into a flow of water, the mixing valve including a valve body defining a first chamber and a second chamber, with the chambers being separated by an internal divider having an orifice which allows fluid to flow between the chambers,

the first chamber having a first inlet port for receiving fire retardant gel under pressure from an external gel source and a first outlet port to enable the gel to be returned to the external gel source, the first chamber otherwise being sealed such that, when the first outlet port is closed, the gel is discharged from the first chamber into the second chamber via the orifice,

the second chamber having a second inlet port for receiving water under pressure from an external water source and having a second outlet port which discharges the water from the second chamber in accordance with the pressure of the water source,

the mixing valve further including a movable valve element located within the first chamber and being movable between:

a closed position in which: (i) an operative surface of the valve element seals the orifice to thereby prevent fluid flow between the chambers, and (ii) the first outlet port is open to allow the gel to return to the external gel source; and

an open position in which (i) the first outlet port is sealed to prevent gel being returned to the external gel source, and (ii) the operative surface of the movable valve element is separated from the orifice to allow the gel to flow through the orifice into the second chamber when the gel pressure is higher than the water pressure, and thus allow the gel to mix with the water prior to being discharged from the second outlet port

[0034] In one embodiment, the movable valve element is biased to the closed position, preferably by a coil spring.

[0035] In a further embodiment, the mixing valve may include an electrically controllable mechanical actuator. The movable valve element may then be drawn away from the closed position, against the bias, by the actuator.

[0036] In one embodiment, the movable valve element includes an elongated shaft having a conical end portion forming the operative surface of the movable valve element. The conical end portion is preferably shaped to extend into and seal the orifice when the elongated shaft is in the closed position.

[0037] In one embodiment, the movable valve element includes a slidable piston which seals the first outlet port, and thereby prevents gel being returned to the external gel source, when the movable valve element is in the open position. In this embodiment the slidable piston may be provided on the elongated shaft of the movable valve element.

[0038] Other preferred features of the mixing valve may be as outlined previously in relation to the first mixing valve described above.

[0039] Throughout this specification, the phrases 'fire retardant gel' and 'gel' are used to refer to any type of fire retardant additive. The additive could be in the form of a viscous gel containing super-absorbent polymers, or it could be a less viscous liquid, with a viscosity similar to that of water. As such, the term 'gel' should be understood to include any fire retardant additive.

[0040] Similarly, the term 'water' is used throughout this specification to refer to any liquid which may be used to extinguish fires. As such, although water may be the most common liquid used, the term should be understood more broadly to include any liquid capable of extinguishing a fire.

[0041] To assist the further understanding of the invention, reference is now made to the accompanying drawings which illustrate preferred embodiments. It is to be appreciated that these embodiments are given by way of illustration only and the invention is not to be limited by this illustration.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a schematic diagram of a first system for delivering a fire retardant gel mixture, in accordance with an embodiment of the present invention.

[0043] Figure 2A is a cross-sectional side view of a first mixing valve for injecting a fire retardant gel into a flow of water in accordance with an embodiment of the invention.

[0044] Figure 2B is a partial side view of the mixing valve shown in Figure 2A, in which additional internal components are represented.

[0045] Figure 3 is an exploded side view showing the components of the mixing valve shown in Figures 2A and 2B.

[0046] Figure 4A is a cross-sectional side view of an extendable mixing valve, shown in its retracted position, in accordance with an alternative embodiment of the invention. [0047] Figure 4B is a partial side view of the extendable mixing valve shown in Figure 4A, in which additional internal components are shown.

[0048] Figure 5 is a partial side view of the extendable mixing valve shown in Figures 4A and 4B, in an extended position.

[0049] Figure 6 is an exploded side view of the extendable mixing valve shown in

Figures 4 A, 4B and 5 showing the components of the extendable mixing valve.

[0050] Figure 7 is a schematic diagram of a second system for delivering a fire retardant gel mixture, in accordance with an alternative embodiment of the invention.

[0051] Figures 8A and 8B are cross-sectional side views of a second mixing valve for injecting a fire retardant gel into a flow of water in accordance with an alternative embodiment of the invention, with Figure 8A showing the closed position and Figure 8B showing the open position.

[0052] Figure 9 is an exploded side view showing the components of the mixing valve shown in Figure 8.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0053] Referring initially to Figure 1 of the drawings, there is shown a schematic diagram of a first embodiment of a system 1 for delivering a fire retardant gel mixture. For simplicity and to improve clarity, the schematic diagram represents only the fluid flow circuits. The electrical control circuits have been omitted. In the diagram, the gel circuits are shown in solid lines and the water circuits are shown in broken lines.

[0054] Referring firstly to the gel circuits, the system 1 includes a gel tank 3 and a gel pump 5 which delivers gel to a ring main 7. In the embodiment shown the tank 3 would be a hopper style tank having a capacity of about 10 litres. Gel is drawn from the bottom of the tank 3 by the gel pump 5. The pump is a positive displacement pump which delivers gel at a pressure of about 400 kPa to the ring main 7. The ring main 7 is configured to extend substantially about the chassis of a fire fighting vehicle (not shown) and has a number of branch pipes 9 extending from the ring main 7.

[0055] In the embodiment shown, gel delivery valves 11, in the form of electrically operated solenoid valves, are arranged to control gel flow from the ring main 7 to the branch pipes 9.

[0056] At the other end of each branch pipe 9 is a mixing valve 13 having a first inlet port 15 configured to receive gel from the branch pipe 9. A second inlet port 17 receives water from a water manifold 19. Each mixing valve 13 is configured to mix the gel with the water prior to discharge to a spray nozzle 21 connected to an outlet port 23.

[0057] Although Figure 1 shows one mixing valve 13 connected to the end of each branch pipe 9, it is also possible that more than one mixing valve may be connected to each branch pipe (or perhaps only to one, or several, of the branch pipes). For example, two or more mixing valves 13 may be connected to one branch pipe 9 such that a single gel delivery valve 11 then controls flow of gel to several mixing valves 13. This arrangement is particularly advantageous when several mixing valves are located in very close proximity to each other because it saves weight and cost.

[0058] In the embodiment shown in Figure 1 there are ten branch pipes 9 leading to ten corresponding spray nozzles 21 located about the vehicle body and arranged so as to provide a relatively uniform gel/water coating over the whole vehicle including its cabin, body and tyres. Each of the spray nozzles 21 is accordingly slightly separated from the ring main 7 and is fed by the corresponding branch pipe 9. In one embodiment, each of the spray nozzles 21 may be provided at an end of a telescopic section which extends between the mixing valve 13 and its corresponding spray nozzle 21. This arrangement will be explained further below. Also, while ten spray nozzles are shown in Figure 1, a fewer or greater number may be employed. For example, 12 nozzles may be provided on a larger six wheel drive vehicle, and fewer than ten may be provided on a smaller vehicle.

[0059] The fire retardant gel delivery system may be provided as a kit for fitting to an existing fire fighting vehicle in which a water tank and water pump already exist.

Alternatively, the system may be installed from the outset as a complete vehicle cabin protection system. In any event, the water circuit of a complete system would include a water tank 25, a water pump 27, a strainer 29, a pressure reducing valve 31 and a water control valve 33 in the form of a normally closed electrically operated solenoid valve. The water control valve 33 thus controls water flow to the water manifold 19 and thus to each of the mixing valves 13. In the prototype system developed by the inventors an existing water pump produced a pressure of about 700 kPa and a pressure reducing valve was introduced to reduce this to about 250 kPa. It will be appreciated that this is less than the 400 kPa pressure produced by the gel pump 5.

[0060] Referring again to the gel circuit, a gel return valve 35, in the form of a normally closed electrically operated solenoid valve, controls the return of gel from the ring main 7 to the top of the gel tank 3. This circulation of gel around the ring main 7 and back into the tank 3 helps to keep the gel emulsified and stop it separating. To further facilitate this mixing, a spray nozzle (no shown) may be included where the gel is returned to the top of the tank 3. In use, a control system is configured to initially close all of the gel delivery valves 11 leading to the branch pipes 9 and open the gel return valve 35. The gel pump 5 is then operated at least for a few minutes to circulate the gel through the ring main 7 back to the tank 3. This recirculation of gel may be undertaken periodically, perhaps each time the vehicle engine is started, or at predetermined intervals. Alternatively, a manually activated push button could be provided in the cabin of the vehicle to initiate charging and/or circulation of gel in the ring main 7.

[0061] In an emergency situation when the fire retardant delivery system is activated, the gel return valve 35 is closed and each of the gel delivery valves 11 are opened.

Simultaneously, the water control valve 33 is opened so as to deliver water from the tank 25 to the spray nozzles 21. The simultaneous operation enables mixing of the water and gel in the mixing valves 13.

[0062] For testing purposes, or possibly also for personnel training, the water system may be operated independently of the gel system. For example, it may be necessary to test the operation of extendable mixing valves to ensure that they fully extend from the vehicle and provide a correct spray pattern.

[0063] In addition to the vehicle cabin protection system shown in Figure 1, the delivery system may also include a spray nozzle directed away from the vehicle. For this purpose, a separately controllable gel delivery valve (equivalent to the valves 11 shown in Figure 1) may be provided to control this separate spray nozzle. In addition, the spray pattern of this nozzle might be controllable and a flexible hose may be connected between the outlet port of the mixing valve and the inlet of the spray nozzle. This would enable fire fighting personnel to direct the gel/water mixture to a desired location. For example, it might be desired to create a fire break ahead of an approaching fire front so that the fire fighting crew can evacuate the area before the fire front arrives.

[0064] Referring now to Figures 2A, 2B and 3, there is shown a first embodiment of a mixing valve 13 for injecting a fire retardant gel into a flow of water. Figure 2A is a cross- sectional side view showing various components of the mixing valve 13. Figure 2B is a similar side view but showing additional components within the valve and Figure 3 is a side view showing a disassembled mixing valve including its various components. The mixing valve 13 shown in these figures is suitable for use in the delivery system 1 shown in Figure 1 and, accordingly, the same reference numerals are used in these figures to denote

corresponding features of the mixing valve 13. It should be understood however that the mixing valve shown in these figures could also be used in systems other than that shown in Figure 1.

[0065] Referring now specifically to Figure 2A, there is shown the mixing valve 13 for injecting a fire retardant gel into a flow of water. The mixing valve 13 includes a valve body 41 and a movable valve element 43. The valve body 41 defines a first chamber 45 and a second chamber 47. The chambers are separated by an internal divider 49 including an orifice plate 51 having an orifice 52 through which fluid may flow between the first and second chambers 45 and 47.

[0066] The first chamber 45 has a first inlet port 15 for receiving fire retardant gel under pressure from an external source such as a branch pipe 9 shown in Figure 1. Otherwise, the first chamber is sealed by a slidable piston 53, described further below. With this

arrangement, gel received at the first inlet port 15 is discharged from the first chamber 45 into the second chamber 47 via the orifice 52 provided in the orifice plate 51.

[0067] The second chamber 47 has a second inlet port 17 for receiving water under pressure from an external source such as the water manifold 19 shown in Figure 1. The second chamber 47 also has an outlet port 23 which discharges the water from the second chamber 47 in accordance with the pressure of the water source.

[0068] In the embodiment shown in Figures 2A and 2B, two first inlet ports 15 and two second inlet ports 17 are shown. Only one of each would typically be used and the other is provided merely for installation convenience (for mounting from the right hand or left hand side, for example) and the other would be plugged.

[0069] In the embodiment shown in Figure 2A the first chamber has a cylindrical internal bore with the divider 49 and orifice plate 51 forming an end wall of the cylindrical bore. In this embodiment, the movable valve element 43 takes the form of an elongated shaft 55 extending longitudinally within the cylindrical bore. The elongated shaft 55 has a laterally extending actuating surface 57 which is sealed against an internal surface 59 of the cylindrical bore by a rubber sealing ring 61 so as to form a slidable piston 53 which is arranged to contain the pressurised gel within the first chamber 45. The pressure of the gel thus pushes against the actuating surface 57 (together with the rubber sealing ring 61) of the slidable piston 53. The rubber sealing ring 61 is included to provide a good seal between the slidable piston 53 and the internal wall 59 of the cylindrical bore.

[0070] The elongated shaft 55 of the movable valve element 43 is biased to a closed position, in which an operative surface of the valve element seals the orifice, by a coil spring 63. As can be seen in Figure 2B, the coil spring 63 is positioned to press against a rear surface of the slidable piston 53. To facilitate assembly of the mixing valve 13 a removable end cap 65 may be provided, together with a dust seal 67.

[0071] In the embodiment shown, the elongated shaft 55 of the movable valve element 43 includes a conical end portion 69. This end portion of the shaft 55 forms the operative surface of the movable valve element 43 which, in the closed position, seals the orifice 52 to prevent fluid flow between the chambers. The orifice 52 is preferably provided with a corresponding conically shaped inner surface to match the conical end portion 69 of the valve shaft 55.

[0072] In use, water is delivered to the second chamber 47 via the second inlet port 17 and discharged via the outlet port 23. Fire retardant gel is delivered to the first chamber 45 via the first inlet port 15 under a pressure which is higher than that of the water. The gel pressure acting on the actuating surface 57 of the slidable piston 53 is sufficient to overcome the bias force of the coil spring 63 such that the whole valve element 43 is pushed away from its closed position. This allows the gel to flow through the orifice 52 into the second chamber 47 (given that the gel pressure is higher than the water pressure). The gel thereby mixes with the water within the second chamber 47 prior to being discharged through a spray nozzle (not shown) connected to the outlet port 23.

[0073] It will be appreciated that the mixing ratio of gel to water is dependent upon the pressure of the gel delivered to the first inlet port, the pressure of the water delivered to the second inlet port, and the size of the orifice between the two chambers. The inventors have undertaken extensive testing to determine appropriate pressures and dimensions to deliver a ratio of about 5% gel to water, this being in the desired ratio for the Barricade® fire retardant gel which was used in the test. It is however considered to be within the capability of persons skilled in the art to determine appropriate pressures and dimensions to achieve any desired mixing ratio so it is considered that these need not be explained further.

[0074] Referring now to Figures 4A, 4B, 5 and 6, there is shown an extendable mixing valve in accordance with an alternative embodiment of the invention. This embodiment is very similar to the mixing valve shown in Figures 2A, 2B and 3 but includes a telescopically extendable section to enable a spray nozzle to be positioned at a distance from a fire fighting vehicle on which the system is installed. In most respects, the components of the extendable mixing valve shown in these figures are the same as those shown in the earlier figures so the same reference numerals are used to denote the same or similar features.

[0075] Figure 4A is a cross-sectional side view showing the various components of the extendable mixing valve. Figure 4B is a similar side view to Figure 4A but showing additional components within the valve. Whilst Figures 4A and 4B show the extendable mixing valve in its retracted position, Figure 5 shows the extended position. Figure 6 shows the component parts of the extendable mixing valve shown in Figures 4 A, 4B and 5.

[0076] As can be seen by comparing the mixing valve shown in Figure 2A with the mixing valve shown in Figure 4A, the primary difference is that the extendable mixing valve includes an elongated outer barrel 71 attached to its outlet port 23. Within the outer barrel 71 is an extendable inner tube 73, which is telescopically slidable between a retracted position as shown in Figures 4A and 4B, and an extended position as shown in Figure 5. A coil spring 75 is located between the inner tube 73 and outer barrel 71 and anchored so as to cause the inner tube 73 to move to its retracted position. For this purpose, the spring 75 is held between loci- nuts 77 secured to an inner end of the slidable tube 73 and an end cap 79 fixed to the barrel 71. A seal 81 is also provided to ensure a fluid tight seal between the inner tube 73 and barrel 71.

[0077] Although not specifically shown in the drawings, a spray nozzle would be connected to the free end of the inner tube 73 (left hand end in the figures). The nozzle can then move between the retracted position, in which it is substantially within an outer profile of a vehicle body, and an extended position in which it stands proud from the body, such that its spray pattern can create a more uniform application of gel/water mixture over the glass and panels of the vehicle.

[0078] Referring now to Figure 7 of the drawings, there is shown a schematic diagram of a second embodiment of a system 101 for delivering a fire retardant gel mixture. Similar reference numerals are used in this figure to denote similar features of the system shown in Figure 1 (incremented by 100). Again, for simplicity and to improve clarity, the schematic diagram represents only the fluid flow circuits. The electrical control circuits have been omitted. In the diagram, the gel circuit is shown in solid lines and the water circuit is shown in broken lines.

[0079] Referring firstly to the gel circuit, the system 101 includes a gel tank 103 and a gel pump 105 which delivers gel to a ring main 107. In this embodiment the tank 103 is a hopper style tank having a capacity of about 4 litres. Gel is drawn from the bottom of the tank 103 by the gel pump 105. The pump 105 is a positive displacement pump which delivers gel at a pressure of about 600kPa to the ring main 107. The ring main 107 is configured to reside within a protective modular enclosure to be situated on a fire fighting vehicle (not shown). [0080] In the embodiment shown in Figure 7, a single mixing valve 113, in the form of electrically controlled mechanical operated valve, is arranged to control gel flow from the ring main 107 to a plurality of spray nozzles 121 via a distribution manifold 119.

[0081] The mixing valve 113 has a first inlet port 115 which receives gel from the ring main 107 and a first outlet port 116 arranged to selectively return gel to the ring main 107. A second inlet port 117 of the mixing valve 113 receives water from a pressure reducing valve 131 within the water circuit, and a second outlet port 123 discharges gel/water mixture to the manifold 119. Inside the mixing valve 113 is a movable valve element (not shown in Figure 7) which is selectively controllable between a (i) closed position in which the gel is not mixed with the water and is instead returned to the ring main 107 via the first outlet port 116, and (ii) an open position in which the gel is not returned to the ring main 107 and is instead injected into the water and then discharged at the second outlet port 123 to the distribution manifold 119.

[0082] The distribution manifold 119 is arranged to deliver the gel/water mix to a number of spray nozzles 121, which may be in the form of fixed spray or extendable spray nozzles, similar to the telescopic arrangement used in the extendable mixing valve shown in Figures 4 A to 6.

[0083] In the embodiment of the system shown in Figure 7 there would be ten spray nozzles 121 located about the vehicle body and arranged so as to provide a relatively uniform gel/water coating over the whole vehicle including its cabin, body and tyres. Each of the spray nozzles 121 is fed by the single distribution manifold 119. Each of the spray nozzles 121 may be provided at an end of a telescopic section, similar to the arrangement described above. Also, while ten spray nozzles are suggested for a typical small fire fighting vehicle, a fewer or greater number may be employed.

[0084] This embodiment of fire retardant gel delivery system may also be provided as a kit for fitting to an existing fire fighting vehicle in which a water tank and water pump already exist. Alternatively, the system may be installed from the outset as a complete vehicle cabin protection system. In any event, the water circuit of a complete system would include a water tank 125, a water pump 127, a strainer 129, a pressure reducing valve 131 and a water control valve 133 in the form of a normally closed electrically operated solenoid valve. The water control valve 133 thus controls water flow to the mixing valve 113 and thus to each of the spray nozzles 121 via the distribution manifold 119. In a prototype system developed by the inventors an existing water pump produced a pressure of about 700 kPa and a pressure reducing valve was introduced to reduce this to about 250 kPa. It will be appreciated that this is less than the 600 kPa pressure produced by the gel pump 105.

[0085] Referring again to the mixing valve 113, a gel return port 116, which is controlled by means of an electrically operated mechanical actuator 183, controls the return of gel from the mixing valve 113 to the top of the gel tank 103. This circulation of gel around the ring main 107 and back into the tank 103 helps to keep the gel emulsified and stop it separating. To further facilitate this mixing, a spray nozzle (not shown) may be included where the gel is returned to the top of the tank 103. The gel pump 105 is operated at least for a few minutes to circulate the gel through the ring main 107 back to the tank 103. This recirculation of gel may be undertaken periodically, perhaps each time the vehicle engine is started, or at

predetermined intervals. Alternatively, a manually activated push button could be provided in the cabin of the vehicle to initiate charging and/or circulation of gel in the ring main 107.

[0086] In an emergency situation when the fire retardant delivery system 101 is activated, the electrically controlled mechanical actuator 183 is operated so as to cause the movable valve element within the mixing valve 113 to close the first outlet port 116 (the gel return port). Simultaneously, the water control valve 133 is opened so as to deliver water from the tank 125 to the spray nozzles 121. This simultaneous operation enables mixing of the water and gel in the mixing valve 113.

[0087] In addition to the vehicle cabin protection system shown in Figure 7, the delivery system may also include a separate spray nozzle directed away from the vehicle. For this purpose, a separately controllable mixing valve (equivalent to the valve 113 shown in Figure 7) may be provided within the ring main to deliver gel/water mixture to this separate spray nozzle. Each mixing valve 113 would effectively be connected in "series" within the ring main 107 and may be operated independently, with the other(s) effectively being bypassed. In other words, the other mixing valve(s) would be "closed" such that the gel is returned to the ring main 107 from the first inlet port 115 to the first outlet port 116 (being the gel return port). In addition, the spray pattern of this separate spray nozzle may be made controllable and a flexible hose may be connected between the outlet port of the associated mixing valve and the inlet of the separate spray nozzle. This would enable fire fighting personnel to direct the gel/water mixture to a desired location.

[0088] Referring now to Figures 8A, 8B and 9, there is shown a second embodiment of a mixing valve 113 which is suitable for use in the system 101 shown in Figure 7. Figure 8 A and 8B are cross-sectional side views showing various components of the mixing valve 113 and Figure 9 is a similar side view showing a disassembled mixing valve. Accordingly, the same reference numerals are used in these figures to denote corresponding features of the mixing valve 113 shown in Figure 7. It should be understood however that the mixing valve 113 shown in Figures 8 A, 8B and 9 could also be used in systems other than that shown in Figure 7.

[0089] Referring now specifically to Figure 8A and 8B, there is shown the mixing valve 113 for injecting a fire retardant gel into a flow of water. Figure 8A shows the "closed" position of the mixing valve and Figure 8B shows the "open" position. The mixing valve 113 includes a valve body 141, a movable valve element 143 and an electrically operated mechanical actuator 183 connected to the movable valve element 143. It should be understood however that, in a further embodiment (not shown), the movable valve element 143 may instead be manually operated lever or the like, rather than being electrically operated.

[0090] The valve body 141 defines a first chamber 145 and a second chamber 147. The chambers are separated by a divider 149 including an orifice bushing 151 having an orifice 152 through which fluid may flow between the first and second chambers 145 and 147 when the movable valve element is in the open position as shown in Figure 8B.

[0091 ] The first chamber 145 has a first inlet port 115 for receiving fire retardant gel under pressure from an external gel source (such as the ring main 107 shown in Figure 7) and a first outlet port 116 for returning gel to the external source. Otherwise, the first chamber 145 is sealed by a bush 185 together with a pair of O-rings 187 such that, when the first outlet port 116 is closed, gel is discharged from the first chamber 145 into the second chamber 147 via the orifice 152 provided in the orifice bushing 151.

[0092] The second chamber 147 has a second inlet port 117 for receiving water under pressure from an external source (such as the water pressure reducing valve 131 shown in Figure 7) and a second outlet port 123 which discharges the water from the second chamber 147 in accordance with the pressure of the water source.

[0093] In the embodiment shown in Figures 8A and 8B, the first chamber 145 has a stepped profile cylindrical internal bore with the divider 149 and orifice bushing 151 forming an end wall of the cylindrical bore (right hand end in the figures). In this embodiment, the movable valve element 143 takes the form of an elongated shaft 155 extending longitudinally within the cylindrical bore. The elongated shaft 155 has a slidable piston 153 which is arranged to block the return of gel to the external gel source by sealing the first outlet port 116 when the movable valve element 143 is in the open position as shown in Figure 8B. More specifically, the slidable piston 153 includes an O-ring 161 to facilitate sealing of the piston against the internal surface 159 of the reduced diameter internal bore.

[0094] The elongated shaft 155 of the movable valve element 143 is biased to the closed position (Figure 8 A) by a coil spring 163. The coil spring 163 surrounds the elongated shaft 155 of the movable valve element 143 and is captured between an end cap 164 of the valve body and a spring stop 166.

[0095] In the embodiment shown, the elongated shaft 155 of the movable valve element 143 includes a conical end portion 169. This end portion of the shaft 155 forms the operative surface of the movable valve element 143 which, in the closed position, seals the orifice 152 to prevent fluid flow between the chambers 145 and 147. The orifice 152 is preferably provided with a corresponding conically shaped inner surface to match the shape of the conical end portion 169 of the valve shaft 155.

[0096] In use, water is delivered to the second chamber 147 via the second inlet port 117 and discharged via the second outlet port 123. Fire retardant gel is delivered to the first chamber 145 via the first inlet port 115 under a pressure which is higher than that of the water. The electrically operated mechanical actuator 183 is used to move the valve element 143 to the open position (Figure 8B) and thereby simultaneously close the gel return port (the first outlet port 116).This allows the gel to flow through the orifice 152 into the second chamber 147, given that the gel pressure is higher than the water pressure. The gel thereby mixes with the water within the second chamber 147 prior to being discharged at the outlet 123, for delivery to the distribution manifold 119 and then to the spray nozzles 121 when the mixing valve 113 is used within the system shown in Figure 7.

[0097] It will be appreciated that the mixing ratio of gel to water is dependent upon the pressure of the gel delivered to the first inlet port, the pressure of the water delivered to the second inlet port, and the size of the orifice between the two chambers. The inventors have undertaken extensive testing and found that using a single mixing valve with multiple spay nozzles, as in the system shown in Figure 7, means a larger orifice can be used and this reduced the likelihood of a blockage within the mixing valve.

[0098] Overall, the fire retardant gel delivery systems of the present invention provide a number of advantages over prior art systems which use water alone. For example, the inventors have found that a minimal amount of water is required to protect a light duty fire fighting vehicle. In this regard, in tests conducted by the inventors, it was found that on average only 40 litres of water was required, together with about 2 litres of fire retardant gel, compared to 600-750 litres when using water alone. [0099] The fire retardant gel effectively forms a 'wet blanket' which covers the vehicle. This wet blanket can be rehydrated if it dries out by supplying only some additional water. In circumstances where the system is used to create a fire break, for example by spraying the gel/water mixture on a section of grass or vegetation along a road, the fire break can be rehydrated simply by respraying the gel coating with water. Additional gel is not required. Thus, the delivery system enables a fire break to be established for an extended period of time by initially coating the grass/vegetation with gel/water mixture and subsequently rehydrating the gel coating when it starts to dry out.

[00100] The use of a plurality of nozzles arranged around the vehicle also helps to provide a reliable coverage and, in tests conducted to date, the inventors have found that about 10 spray nozzles provide optimal coverage.

[00101] Although the inventors' tests to date have been conducted using the Barricade® brand of fire retardant gel, other gels or liquids could alternatively be used. Different fire retardants would require different mix ratios and this could be readily achieved with the mixing valve of the present invention by simply varying the respective pressures and the size of the orifice. In this regard, the use of an orifice plate, as in the preferred forms of the mixing valves shown in the drawings, allows different orifice plates to be installed according to the particular fire retardant being used.

[00102] Finally, although preferred embodiments of the invention are described herein in detail, it will be understood by those skilled in the art that variations may be made thereto without departing from the spirit of the invention or the scope of the appended claims.