Here the term'water-based liquid'means pure water or different water-containing additives, depending on the purpose for which the liquid is used.

US 4326589 discloses a similar power source used for fire fighting.

Power sources for supplying water to various systems, the power source comprising a container for the water and a pump unit for supplying the water from the container to the system via a pipe system which is filled with water, are very commonly used e. g. in houses, for supplying water from a fresh water source, such as a well, to the pipe system of the house. Another application for such power sources are fire fighting installations.

The present invention also relates to a fire fighting installation com- prising a spray head and a power source for supplying water-based liquid, through a pipe system which is filled with antifreeze, to a unit which is to be protected against fire, a container for the water-based liquid, an additional container which is filled with antifreeze and means for feeding water-based liquid which has a tendency freeze into and out of the pipe system in liquid phase if the pressure in the pipe system drops below a certain level, being associated with the pipe system.

Certain environments where water or water-based liquid is to be supplied involve a risk of freezing. This problem is common in various situa- tions in countries where the temperature drops below the freezing point of water. Some applications are related to a system without recirculation, i. e. a system where the amount of liquid decreases as it is used for a specific pur- pose. An example of the last-mentioned is a fire fighting installation which

uses water-based liquid as extinguishant. In these it is particularly important that the extinguishant does not freeze because in that case the installation cannot work.

In several applications the problem of freezing is solved by mixing a substance which prevents freezing into water. However, the substances which prevent freezing, or antifreezes, are expensive; in fact much more expensive than water or water-based liquid. The larger the system and the liquid volume, the more expensive addition of antifreeze is. Because of this, the use of anti- freezes in power sources with large containers involves the problem of high costs.

An example of applications where the above-mentioned problems occur is a fire fighting installation which is dimensioned for larger fires and in which the consumption of extinguishant is high. Furthermore, if anti-freeze is mixed into water or water-based liquid in a fire fighting installation which uses water-based liquid, the resulting extinguishant will have a poorer extinguishing capability than a liquid into which antifreeze has not been mixed. Thus the use of antifreezes leads to a further problem of poor function.

To avoid high costs, substances which prevent the risk of freezing are sometimes omitted from the water-based liquid, which can have serious consequences in fire fighting installations, for example. The water-based liquid may also be replace with a fluid which is harmful to the environment. Fur- thermore, in some cases the amount of water can be reduced, but in fire fighting installations, for example, this naturally involves a risk.

US 4326589 discloses a fire fighting installation utilizing initially an- tifreeze in the pipe system whereafter water is delivered to sprinklers.

BRIEF DESCRIPTION OF THE INVENTION An object of the present invention is to provide a power source for supplying water-based liquid which enables automatic supply of water-based liquid to the system without the risk of freezing and by using only a small amount of expensive substances which prevent freezing of water.

To achieve this object, the power source is characterized in that that the means for feeding the water-based liquid from the container com- prises as part of the power source a pump unit comprising a pump and a power source for the pump and that the power source comprises an additional pump unit comprising a pump and a power source for the pump, the additional

pump unit being arranged to maintain the stand-by pressure in the pipe sys- tem and to supply for this purpose antifreeze from the additional container to the pipe system if the pressure in the pipe system drops below the stand-by pressure by a second pressure value giving momentarily rise to a second pressure level in the pipe system, the second pressure level being bigger than the first pressure level Since antifreeze is needed only in those sections of the system which may be exposed to frost, the volume of the additional container can be several times smaller than that of the container where water-based liquid is used. Naturally this requires that the container filled with water-based liquid has to be situated in a place where the water-based liquid cannot freeze.

The preferred embodiments of the power source are disclosed in appended claims 2 to 11.

The major advantage of the power source is that it allows to mini- mize the use of expensive substances which prevent freezing of water, which is particularly significant when the container is large, i. e. in connection with a system which uses large amounts of liquid which should not freeze.

The fire fighting installation of the invention is characterized in that the means for feeding the water-based liquid from the container comprises as part of the power source a pump unit comprising a pump and a power source for the pump and that the power source comprises an additional pump unit comprising a pump and a power source for the pump, the additional pump unit being arranged to maintain the stand-by pressure in the pipe system and to supply for this purpose antifreeze from the additional container to the pipe system if the pressure in the pipe system drops below the stand-by pressure by a second pressure value giving momentarily rise to a second pressure level in the pipe system, the second pressure level being bigger than the first pres- sure level.

In the power source and fire fighting installation of the invention liq- uid with the risk of freezing is replaced with antifreeze only when it is neces- sary, i. e. in environments where there is time for the liquid with the risk of freezing to freeze and in which liquid with the risk of freezing can be used for a short period, i. e. when there is no time for the liquid with the risk of freezing to freeze.

The fire fighting installation is particularly suitable for trains. This application allows to lower the costs of the extinguishant considerably.

The preferred embodiments of the fire fighting installation are dis- closed in appended claims 13 to 15.

The major advantage of the fire fighting installation is that the costs of the extinguishant can be kept low, especially in applications where the amount of extinguishant should be large. At the same time, the extinguishant has a good extinguishing capability and cannot practically freeze.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, the invention will be described in greater detail by means of an example with reference to the attached figure which shows a fire fighting installation in a railway carriage and the power source for the fire fighting installation.

DETAILED DESCRIPTION OF THE INVENTION The figure shows a system which comprises three railway carriages 1,2,3 of a train. One carriage 3 of the railway carriages comprises a power source with pump units 6,10. The last-mentioned railway carriage 3 could be called a pump carriage. The train is provided with a fire fighting installation which comprises the above-mentioned power source and several spray heads 15. The power source is arranged to supply extinguishant in the form of water- based liquid to the spray heads 15 via a pipe system 4. The railway carriages 1,2 are provided with detectors 19 and section valves 20 by means of which the desired groups of spray heads can be released in the event of fire. Alter- natively, all spray heads 15 in a railway carriage can be arranged to be re- leased when a fire is detected in the carriage concerned. The spray heads 15 can also be arranged to be released separately, in which case they typically comprise heat-activated release devices and are released when their release device explodes or melts in the heat.

The power source comprises a large container 5 filled with water- based liquid. Since the container 5 is in the pump carriage which functions as a space which is heat-insulated against the environment, there is no risk of the liquid freezing which could otherwise be possible in the environment of the fire fighting installation. The container 5 has a large volume, e. g. 20-30000 I. A pump unit 6 is arranged to feed water-based liquid from the container 5 to the pipe system 4 via a pipe, the unit comprising a high-pressure pump 7 which can generate a pressure of e. g. 50 to 200 bar and a diesel engine 8 with an output of e. g. 200 kW as a power source for the pump.

The power source comprises an additional container 9 which is filled with antifreeze. A pump unit 10 which comprises a pump 11 and an elec- tric motor 12 as the power source for the pump is arranged to feed antifreeze from the container 9 to the pipe system 4 via a pipeline 13. There is a pressure indicator 14 and an accumulator 16 connected to the pipeline 13.

A valve 17 is attached to the pipeline 13 between the container 9 and the carriage 1. The valve 17, when closed, prevents liquid from flowing back to the container 9.

In the following, it will be explained how the system shown in the figure functions.

In the example, the pipe system 4 is filled with antifreeze. Thus the pipe system 4 can be placed in an environment where the temperature drops below the freezing point of water without the liquid freezing in the pipe. In the pipe system 4 there is a stand-by pressure of e. g. 10 to 30 bar before the spray heads 15 start to function. Since the pipe system 4 typically continues from one carriage to several other carriages, there has to be couplings 18 between the carriages which can be locked and unlocked as railway carriages are attached to and detached from the train.

In practice, the pressure changes in the pipe system 4 although no spray head 15 is released. To make sure that the pipe system 4 is always filled with liquid and to level the pressure changes, the pump unit 10 is ar- ranged to maintain the above-mentioned stand-by pressure in the pipe sys- tem. The pressure indicator 14 controls the stand-by pressure so that it starts the motor 12 if the pressure in the pipe system 4 drops below the stand-by pressure by a second pressure value giving momentarily rise to a second pressure level in the pipe system. The second pressure level is only slightly smaller than the stand-by pressure. The second pressure level is e. g. 20 bar.

If the pressure rises over a certain higher value, e. g. 30 bar, because the pump unit 10 has raised the pressure, the pressure indicator 14 makes the motor 12 stop. So that the motor 12 would not be switched on and off several times at short intervals, the accumulator 16 is arranged to supply antifreeze to the pipeline 13 and pipe system 4. Thus the accumulator 16 functions as a buffer.

If the spray head 15 of the fire fighting installation starts to spray liquid as a result of the fact that a detector 19 has reacted to a fire and given a signal to open a section valve 20, the pressure in the pipe system 4 drops by a

first pressure value giving rise to a first pressure level in the pipe system 4.

When the first pressure level is e. g. 5 bar, the pressure indicator 14 reacts to the pressure drop and gives a signal to the diesel engine 8 so that it starts, in which case the pump 7 starts to pump water-based liquid into the pipe system 4 at high pressure. The pressure is preferably in a range of 50 to 200 bar, for instance. A check valve 25 prevents high pressure liquid form flowing against and into the additional pump unit 10. Since the temperature of the water-based liquid is relatively high and it is carried in the pipe system at a relatively high rate, the temperature of the liquid does not have time to drop so much that the liquid would freeze. Consequently, the liquid flows out of the spray heads 15.

The pressure indicator thus controls the power sources of both pump units, i. e. the electric motor 12 and the diesel engine 8. Instead of a pressure indicator 14, it is possible to use a number of pressure switches which give signals to the pump units when the pressure drops below a certain level or exceeds it.

Since antifreeze is only needed to compensate for a possible leak- age in the pipe system 4 before the fire fighting installation starts to spray ex- tinguishant, the volume of the container 9 can be several times smaller than the volume of the large container 5. The volume of the container 9 could be e. g. 100-3001.

Reference number 21 denotes a shut-off valve which prevents the pump unit 10 from feeding antifreeze into the pipe system 4 at too high a pres- sure, which may be generated if the pressure indicator 14 does not function properly and which could damage a component of the power source. If a pres- sure higher than 30 bar is generated, it is led back to the container 9 via a pipe 24. The shut-off valve 21 functions as a safety valve.

Reference number 22 denotes a shut-off valve which prevents the pump unit 6 from feeding water-based liquid into the pipe system 4 at high pressure, e. g. over 200 bar, if the pressure indicator 14 does not function properly. Such a pressure is led back to the container 5 via a pipe 23. The shut-off valve 22 has the same function as the shut-off valve 21, and thus it can also be called a safety valve.

In the above, the invention has been described only by means of one example. Therefore it is emphasized that the details of the invention may vary in several ways within the scope of the appended claims. The structure of the pump units, for example, may vary. The engine 8 could be an electric mo-

tor and the motor 12 a diesel engine. The containers 5,9 may differ from what has been described above; however, the basic idea does not change, i. e. the container 5 is considerably larger than the container 9 as well as very large in absoute terms, typically thousands of liters. The system can be used in a place other than a railway carriage, and it does not need to comprise a fire fighting installation, although the invention is particularly suitable for fire fight- ing installations. The antifreeze, which in the example is in the pipe system, is preferably, but not necessarily, the same antifreeze as that used in the addi- tional container 9.