The present invention relates to a fire- fighting installation comprising a liquid source and a gas source connected by way of a line to an outlet line of the liquid source for mixing gas with outbound extinguishing liquid delivered to spray heads.

Certain kinds of gasoline fires, for example a kerosene fire in an aircraft jet engine undergoing an engine test in a hangar designed for that purpose, are nearly impossible to extinguish even by means of strong mist-like jets of liquid, as suggested for example in international patent application PCT/FI92/00155. Such a jet engine fire will only go out when the entire hangar, which may typically have a volume of about 3000 cm ³ , has been subjected to "total flooding", i.e. is in practice entirely filled with liquid mist having very small particles.

The liquid mist can in principle be produced with apparatus as described in international patent application PCT/FI92/00317. In that application, an outgoing ascension tube of a hydraulic accumulator is provided with wall apertures, so that the propellent gas of the accumulator initially drives out liquid only, and after the liquid level has sunk to be even with the uppermost tube wall aperture, mixing of gas into the outbound liquid is gradually started as the liquid level sinks and more tube wall apertures are exposed. In the final stage of emptying the accumul- ator, it is possible to obtain a liquid mist having sufficiently small droplets for the present purpose, but too large a portion of the liquid contained in the hydraulic accumulator will go waste.

It is an object of the present invention to provide a novel installation enabling effective

delivery of liquid with immediate effective mixing of gas into the liquid right from the start.

The installation in accordance with the inven¬ tion is characterized in that the liquid source com- prises a hydraulic accumulator having at least one liquid tank, and that the gas source comprises at least one compressed-gas vessel connected to the liquid tank in such a way that the compressed-gas vessel and liquid tank form communicating vessels, the compressed-gas vessel being adapted to mix gas into the extinguishing liquid delivered to the spray heads to produce a finely divided liquid mist.

A preferred embodiment of the invention is characterized in that a compressed-gas container is coupled to the liquid tank for driving out liquid from said at least one liquid tank, the compressed-gas vessel forming communicating vessels with the liquid tank and the compressed-gas source. Preferred embodi¬ ments of the invention are set forth in the appended claims 2-10.

The proportion of gas mixed into the extin¬ guishing liquid is determined by the proportion of the volumes of the propellent gas container of the liquid source and the compressed-gas container of the gas source.

If the propellent gas container of the liquid source and the gas source have the same initial charge pressure, gas is mixed into the extinguishing liquid from the start. If the propellent gas container of the liquid source has a higher initial charge pressure than the gas source, only liquid is discharged from the spray heads in a first step, until the pressure in the propellent gas container of the liquid source has decreased to equal the pressure of the gas source. In the following the invention will be

described with reference to the accompanying drawing showing two preferred embodiments of the installation in accordance with the invention.

Figure 1 shows an embodiment having separate sources for propellent gas and gas to be mixed into the extinguishing liquid.

Figure 2 shows an embodiment in which a common source for propellent gas and gas to be mixed into the extinguishing liquid is provided. The embodiment shown in Figure 1 comprises a hydraulic accumulator, having an outlet line 2 leading to a plurality of spray heads 3 via a valve 12. A com¬ pressed-gas container in the form of a compressed-gas bottle 4 is connected to the outlet line 2 by way of a line 10. The hydraulic accumulator incorporates two liquid tanks 1, the outlet tubes of which may be pro¬ vided with apertures, as in international patent application PCT/FI92/00317, and a propellent gas bottle la. The liquid tanks 1 may contain for example water. The liquid is driven out from the tanks 1 by means of propellent gas delivered from the propellent gas bottle la.

The propellent gas bottle la may be filled with nitrogen, argon, air, etc. In principle, any suit¬ able gas can be used. The initial charge pressure of the propellent gas bottle la is for instance 100-200 bar. The compressed-gas bottle 4 may contain nitrogen, argon, air, etc. In principle, any suitable gas is possible. The initial charge pressure of the propellent gas bottle la is the same or higher than the initial charge pressure of the compressed-gas bottle 4. The contents of the propellent gas bottle la and com¬ pressed-gas bottle 4 may be partially in liquid form, depending on the type of gas employed.

The liquid tanks 1, propellent gas bottle la and compressed-gas bottle 4 form communicating vessels, and thus the emptying of each will be automatically continued until all liquid has been driven out. The proportion of gas to be mixed from bottle 4 is dependent on the ratio between the volumes of the propellent gas bottle la and the compressed-gas bottle 4. The quantity of liquid relative to the quantity of propellent gas determines the length of the flow; the more liquid, the longer the flow and the lower the final pressure in the propellent gas bottle la and the compressed-gas bottle 4.

Figure 2 shows another embodiment of the installation of the invention. This embodiment differs from the embodiment of Figure 1 mainly in that the pro¬ pellent gas source for driving liquid out of the liquid tank 1' and the compressed-gas source for mixing gas into the liquid in the line 2' are constituted by the same source 4' . This source is a compressed-gas bottle 4' filled with nitrogen and having an initial charge pressure of approximately 100-200 bar. A line 10' has been coupled between the compressed-gas bottle 4' and the outlet line 2' of the liquid tank 1' .

In the embodiment of Figure 2, valve 12' has been connected between the throttle 11' and the com¬ pressed-gas bottle 4' for activating and alternatively passivating the installation. The valve could, however, be connected directly to the line 2' , as in Figure 1. The purpose of the throttle 12' is to induce a comparatively large gas flow from the compressed-gas bottle 4' to the liquid tank 1' by choking the gas flow, in which situation the gas flow from the throttle directly to the outlet line 2' is relatively small. In this situation, the throttle 12' adjusts the mixing ratio of liquid and gas in the extinguishing fluid

gushing into the outlet line 2' . The throttle 12' is not indispensable. It could be contemplated that the mixing ratio could be adjusted by the dimensioning of the line between branching point 13' and the outlet line 2' .

The invention has been illustrated in the above by way of examples, and it is therefore to be noted that the invention can vary in its details in many ways within the scope of the appended claims. Hence, for example, any compressed-gas vessel may be employed as a compressed-gas bottle 4, 4'. The number of compressed-gas vessels and compressed-gas containers may vary.