Fire extinguishers – Special applications – Condition responsive control
Patent
1994-12-12
1997-04-22
Pike, Andrew C.
Fire extinguishers
Special applications
Condition responsive control
169 38, A62C 3714
Patent
active
056222254
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to fire fighting equipment having a release device that is activated at a predetermined release temperature. The release device may be, e.g., a glass ampoule or a fuse, which breaks or melts, respectively, at the predetermined release temperature and thereby releases, i.e., activates, a spray head to spray extinguishing liquid.
The nominal release temperature may be, e.g., about 70.degree. C. Usual release elements are, however, heated up to the release temperature rather slowly. At a fire in a hotel room or in a ship cabin, for example, the temperature in the room or cabin has time to rise to some 300.degree. C.-400.degree. C. before release takes place in conventional sprinkler installations.
Recent so-called fast response sprinklers are, in similar situations, capable of release at a room or cabin temperature of about 200.degree. C.-250.degree. C. A measure of the release rate generally used is a so-called Response Time Index (RTI). Conventional sprinklers have a Response Time Index of about 300; the "fast" sprinklers mentioned above have a Response Time Index of about 50.
SUMMARY OF THE INVENTION
The object of the present invention is to provide new fire fighting equipment which is released considerably faster than earlier known designs.
The fire fighting equipment according to the invention is mainly characterized in that an element of memory metal is immediately close to the release device. The element of memory metal changes shape at a predetermined memory temperature to close an electric circuit for heating the memory metal element and, thereby, the device means to effect its fast release action. As used herein, therefore, "immediately close" means sufficiently close for the element of memory metal to heat the release device.
The element of memory metal is preferably a wire helically laid around the release device.
The memory metal can preferably be a NiTi-alloy with a memory temperature of about 70.degree. C.
At a certain predeterminable memory temperature such a memory metal wire takes a previously "taught" shape. At lower temperatures the wire can be deformed practically at will without mentionable mechanical resistance.
Thus, a helical spring can be "taught" to "remember" a certain length at a temperature of about 70.degree. C. Thereafter the spring can be compressed at, e.g., room temperature to another length, which it retains until the temperature of the spring rises to the memory temperature, whereupon the spring returns to its "taught" length.
In the present invention this property is utilized for closing an electric circuit at the memory temperature, preferably by making contact to suitable metal parts of a sprinkler included in the electric circuit.
The wire of memory metal can be thin, with a diameter of, e.g., 0.3 mm, whereby it is rapidly heated by surrounding hot smoke gases from a fire. When it them establishes a conducting connection, the memory metal wire immediately heats up further and conveys its heat to the release device formed, e.g., by a conventional glass ampoule which is broken in about two seconds.
Thanks to the invention, a Response Time Index of less than 10 can be achieved which, in the fire situations earlier referred to, results in extinguisher release at a room or cabin temperature of less than 100.degree. C. This means that fires are fought in their initial stage and the generation of poisonous smoke gases can be decisively restricted.
BRIEF DESCRIPTION OF THE DRAWING
In the following the invention will be described with reference to the attached drawing which, by way of example, shows a preferred embodiment.
FIG. 1 shows a section of a sprinkler with a helical spring of memory metal around a release device at normal temperature.
FIG. 2 shows the section of the sprinkler in an initial stage at a raised temperature.
FIG. 3 shows the section of the sprinkler in an activated state.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the drawing, reference numeral 1 generally indicates a sprinkler the housing
REFERENCES:
patent: 1392593 (1921-10-01), Newton
patent: 2245144 (1941-06-01), Griffith
patent: 3726344 (1973-04-01), Rothman et al.
patent: 4596483 (1986-06-01), Gabriel
patent: 5361847 (1994-11-01), Phelps
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