SYSTEM"

Cross-Reference to Related Applications This Patent Application claims priority from Italian

Patent Application No. 102021000010364 filed on April 23, 2021, the entire disclosure of which is incorporated herein by reference.

Technical Field of the Invention The present invention concerns a fire extinguishing system for a firefighting vehicle or device, in particular a compressed air foam system (CAFS) provided with an improved mixing system.

State of the Art Firefighting systems, e.g. firefighting vehicles or devices, are provided with fire extinguishing systems configured to supply a fire extinguishing compound to be directed towards a fire in order to lead to its suppression.

In particular, compressed air foam systems (CAFS) are widely known in the art and are directed to the use a mixture of a preset percentage of compressed air and a water/foam agent solution.

In greater detail, the water/foam agent solution comprises a foam agent additive dissolved into a great quantity of water, i.e. from 0,5 to 3% or to 8% in volume of additive. The compressed air is mixed to such solution into a mixing chamber module.

Such air-solution mixture is at higher pressure with respect to atmospheric pressure and is ejected by an outlet of a pipe directed to the fire, it expands forming a foam which has the properties to extinguish the fire. In particular, the air quantity of the foam can be regulated to assume a value comprised between 3 to 20 volume parts of air with respect to liquid solution. As defined in standard DIN EN 16327, such an air/solution ratio comprised between 3 and 10 is defined a "wet foam", while an air/solution ratio comprised between 11 and 20 is defined a "dry foam".

According to the above, one issue related to a CAFS system is to guarantee a correct mixture between the water and the water/foaming solution to provide a suitable air/solution mixture.

However, the air flow and the water flow may vary continuously because the flow or air/solution mixture can be continuously changed by the operator according to the condition of the fire. Such oscillations in water flow may lead to a not satisfactory mixing between water, air and foam agent.

Indeed, water is generally regulated by a butterfly valve, usually closed when the compressed air foam system is engaged, that does not provide a good velocity of the water flow to guarantee a correct mixing between water, foam agent and air. This drawback is particularly present if the requested water flow is low.

Therefore, the need is felt to provide CAFS system that can provide a good mixing between water, the foam agent and air according to user's necessities.

An aim of the present invention is to satisfy the above mentioned needs in a cost-effective and optimized way.

Subject and Summary of the Invention The aforementioned aim is reached by a compressed air foam systems as claimed in the appended set of claims.

Brief Description of the Drawing For a better understanding of the present invention, a preferred embodiment is described in the following, by way of a non-limiting example, with reference to the attached drawing, figure 1, showing a schematic representation of a compressed air foam system comprising a mixing module according to the invention. Detailed Description of Preferred Embodiments of the

Invention

Figure 1 discloses a general schematic representation of a compressed air foam system, CAFS, 1 for a firefighting utility, e.g. a vehicle, not shown. The CAFS 1 essentially comprises a source 2 of water, an air management system 3, a solution dosing system 4 and a mixing chamber 5. The mixing chamber 5 receives water from the source 2, a controlled and defined air flow from air management system 3, an additive agent from solution dosing system 4, e.g. a foam agent and is configured to mix together such elements to provide a suitable flow of firefighting air/solution mixture at an outlet device 6 that may be connected to a pipe used by a fireman.

The air management system 3 may be realized in different way, e.g. according to the system described in international patent application PCTIB2020061830 and therefore not further described herein for sake of brevity.

Also the solution dosing system 4 may be realized in different known ways. Both the solution dosing system 4 and the air management system 3 are configured to provide respective pressurized fluid flows into mixing chamber 5 of, respectively, foam solution and compressed air.

The source 2 of water may be of different typologies such as a water pump, a hydrant, as known in the field.

Preferably, the mixing chamber 5 defines a first inlet 5a fluidly connected to source 2, a second inlet 5b fluidly connected to an output 4a of dosing system 4 , a third inlet 5c fluidly connected to an output 3a of air management system 3 and an outlet 5d fluidly connected to outlet device 6.

According to the described embodiment, the mixing chamber 5 comprises an inlet conduit 7, an outlet conduit 8 and a plurality of by-pass conduits 9a, 9b, 9c, 9d fluidly interposed in parallel between inlet conduit 7 and outlet conduit 8.

In the following, the terms "upstream" and "downstream" are used referring to the water path from source 2 to outlet device 6.

The inlet conduit 7 is fluidly connected to source 2 from one side and to by-pass conduits 9a, 9b, 9c, 9d, 9e downstream to source 2 while the outlet conduit 8 is fluidly connected to outlet device 8 from one side and to by-pass conduits 9a, 9b, 9c, 9d, 9e upstream to outlet device 6.

In detail, a first by pass conduit 9a is upstream to a second by-pass conduit 9b that is upstream to a third by pass conduit 9c that is upstream to a fourth by-pass conduit 9d that is upstream to a fifth by-pass conduit that is downstream to only source 2. In other words, from outlet device 6 points of view, first by pass conduit 9a is upstream to second by-pass conduit 9b that is upstream to third by pass conduit 9c that is upstream to fourth by-pass conduit 9d that is up stream to fifth by-pass conduit that is upstream to only outlet device 6.

In particular, output 4a of dosing system 4 and output 3a of air management system 3 are both fluidly connected to only first by-pass conduit 9a, i.e. the by-pass that is most downstream with respect to source 2. More preferably, output 3a of air management system 3 is fluidly connected to first by-pass conduit 9a upstream to outlet conduit 8 and downstream to output 4a of dosing module 4. Dosing module output 4a is fluidly connected to first by-pass conduit 9a downstream to inlet conduit 7.

Advantageously, the number of by-pass conduit conduits 9a, 9b, 9c, 9d, 9e is N and the hydraulic diameter of an

(M)-th by-bass conduit 9a, 9b, 9c, 9d, 9e) is lower with respect to the (M+l)-th by-bass conduit conduits (9a, 9b, 9c, 9d, 9e), wherein N and M are an integer number and M is smaller than N.

According to the described embodiment, the first conduit 9a has a hydraulic diameter that is smaller with respect to second conduit 9b that is smaller with respect to third conduit 9c that is smaller with respect to fourth conduit 9d that is smaller with respect to fifth conduit 9e. Preferably, inlet and outlet conduit 7 has a hydraulic diameter that is substantially the same as the fifth conduit 9e or greater. More preferably, outlet conduit 8 has a variable diameter between conduits 9a and 9e. In particular, the section of outlet conduit 8 between (M)-th conduit and (M+l)- th conduit has substantially the same diameter of the (M)- th conduit.

Accordingly, the section of outlet conduit 8 between b conduits 9a and 9b has substantially the same diameter of conduit 9a, the section of outlet conduit 8 between conduits 9b and 9c has substantially the same diameter of conduit 9b, the section of outlet conduit 8 between conduits 9c and 9d has substantially the same diameter of conduit 9c, the section of outlet conduit 8 between conduits 9d and 9e has substantially the same diameter of conduit 9d and then the last section has the same diameter of conduit 9e, i.e. the diameter of input conduit 7. Advantageously, at least some among the by-pass conduits 9a, 9b, 9c, 9d, 9e is provided with valve means 10 configured to allow the passage of fluid through the respective by-pass conduit only from inlet conduit 7 towards outlet conduit 8. In particular such valve means comprises different pressure control openings thereby allowing to water to flow on the respective by-pass conduit in function of the pressure of water in inlet conduit 7.

In particular, in the disclosed example, the first by pass conduit 9a, i.e. the by-pass conduit directly fluidly connected to air management system 3 and dosing module 4, is free, i.e. always allows fluid passage from inlet conduit 7 towards outlet conduit 8. In other words first by-pass conduit 9a is not provided with the aforementioned valve means.

Advantageously, the other by-pass conduits 9b, 9c, 9d provided with check valve 10 have different opening pressures, i.e. the respective check valves 10 are dimensioned thereby allowing the fluid passage at different pressure levels. In detail, the check valve 10a on second by-pass conduit

9b has an opening pressure level that is lower with respect to the check valve 10b on third by-pass conduit 9c that has an opening pressure level that is lower with respect to the check valve 10c on fourth by-pass conduit 9d. Advantageously, one among the by-pass conduits 9a, 9b,

9c, 9d, 9e is provided with valve means 11 configured to be actively controlled to allow the passage of fluid from said inlet conduit 7 to said outlet conduit 8.

In particular, the fifth by-pass conduit 9e is provided with an electro actuated valve 11, such as an ON-OFF valve, configured to allow or deny the fluid passage from inlet conduit 7 towards outlet conduit 8.

The operation of a OAFS 1 according to the present invention and as described above is the following. In general, the water provided by source 2 flows towards inlet conduit 7 and flows to first by-pass conduit 9a. In such conduit, that has the smallest hydraulic diameter, increases the velocity of water that is mixed first with foam agent coming from opening 4a and then with compressed air coming from opening 3a. Then it passes to outlet conduit that has a greater diameter and allows a good mixing of the water, at high velocity and premixed with foam agent, with compressed air. Then the mixed solution flows towards outlet device 6. If the water pressure increased, then check valve 10a of second by-pass spring opens and allows to the water to pass directly into outlet conduit 8 downstream to second by pass conduit 9b. In this way the solution is furthermore mixed before passing to outlet device 6. Similarly occurs if water pressure further increases thereby allowing the opening of check valves 10b, 10c of third and fourth by-pass conduits 9c, 9d.

If the user needs only water, without foam solution and air, then valve 11 may be controlled to be opened thereby allowing the passage of water flow mainly in fifth by-pass conduit 9e directly to output device 6. Indeed, only a few amount of water flows through conduits 7, 9a and 8 to mix again into output conduit 8; however, due to diameter difference, the main portion of water passes directly through conduit 9e.

In view of the foregoing, the advantages of a compressed air foam system, CAFS, 1 according to the invention are apparent.

Thanks to the proposed mixing module it is possible to mix water with foam solution and air in a very effective way avoiding bad quality foam-solution at outlet device.

Moreover, the mixing module is particularly compact and cost-effective.

Furthermore, the mixing module operates in a very wide range of water pressure with the same quality of foam mixture production.

In addition, by varying the number of by-pass conduits it possible vary the water pressure range. Accordingly, the proposed mixing module is versatile and allows production economic of scale.

In particular, the versatility of the proposed mixing system is clear. Indeed, the mixing system may be used for providing foam solution without air, air-foam solution or simply water to the output device. Accordingly, with respect to known system the mixing system provides all function via a single module.

It is clear that modifications can be made to the described compressed air foam system, CAFS, 1 which do not extend beyond the scope of protection defined by the claims. For sake of example, the number of by-pass conduits may vary. Similarly, valve means 10, 11 may be substituted by different typologies of valves having the same opening characteristics.