US2762998A - Fire alarm system - Google Patents

Description

p 11, 1955 E. M. TALBOTT, JR 2,762,998

FIRE ALARM SYSTEM Filed March 25, 1954 2 sheefs-sheef. 1

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Sept. 11, 1 E. M. TALBOTT, JR

FIRE ALARM SYSTEM 2 Sheets-Sheet 2 Filed March 25, l954 INVENTOR. Eda/LIZ M. Talboiig'Jr.

nited States Patent-O FIRE ALARM SYSTEM Edwin M. Talbott, Jr., Baltimore, Md., assignor to Bendix Aviation Corporation, Baltimore, Md., a corporation of Delaware Application March 25, 1954, Serial No. 418,580

2 Claims. (Cl. 340-289) This invention relates to a system for indicating to a watchman or other attendant at a point remote from the location in which a fire extinguishing system may be installed when the latter as a whole or any part thereof becomes activated as the result of a fire or high temperature condition.

The alarm system of the subject invention is primarily adapted for use with fire extinguishing systems of the sprinkler type, or those involving a system of piping or conduits through which an extinguishing fluid, such as water, flows when a fuse plug or analogous device becomes effective to release the fluid to .and through the sprinkler heads. Systems of the sprinkler type may be further classified as of the wet type, wherein the Water or extinguishing fluid is constantly being maintained in all branches of the system, including the piping which extends to the various sprinkler heads; and the dry type wherein there is a so-called dry-pipe automatic release valve which bars the water from predetermined sections of the piping, including the piping which extends to the various sprinkler heads; and the dry type wherein there is a so called dry-pipe automatic release valve which bars the water from predetermined sections of the piping, including the piping which extends directly to the sprinkler heads, air being trapped in the piping beyond the valve, subject to release should the fuse plugs of the sprinkler heads melt. The drytype sprinkler system eliminates danger of freezing in piped areas where temperatures may drop to below 32 F. One of the hazards of such systems is that should a leak develop in the dry piping and remain undetected, water may seep into the latter piping and freeze, with resulting danger of serious impairment.

One of the objects of the invention is to provide an improved warning or alarm system of the tune specified which will indicate to a watchman or other attendant at a point remote from the location in which a fire extinguishing system may be installed, not only when the system as a whole becomes activated as the result of a fire or high temperature condition, but also the particular branch of the system which is being activated.

Another object is to provide an alarm system particularly adapted for dry-type sprinkler systems which will not only indicate to a watchman or attendant when the system as a whole or any part hereof may become activated, but also when and if a leak develops during inactive periods which would cause flow of extinguishing fluid beyond the dryapipe automatic release valve.

Another object of the invention is to provide a warning or alarm system which may be installed in conjunction with either a wet or dry-type sprinkler system and which involves parts not subject to deterioration through corrosion or other factors resulting from idleness over long periods of time, and which is reliable in operation and may be maintained indefinitely at its initial installation efiiciency with a minimum of attendance and maintenance expense.

Another object is to provide a warning or alarm sysice Another object is to provide an electric alarm or warn- 4 ing system for fire extinguishing systems of the fluid flow type which incorporates a simple, easily removable and replaceable resistance element as the basic automatic circuit control, together with associated circuitry arranged for convenient maintenance under varying climatic and localized temperature and humidity conditions.

A further object is to generally improve and simplify fire alarm systems of the sprinkler type.

The foregoing and other objects and advantages will become apparent in the light of the following description taken in conjunction with the drawings, wherein:

. Fig. 1 is a wiring diagram of a system embodying the features of the invention;

Fig. 2 is a schematic view of a dry pipe sprinkler system incorporating the alarm system illustrated in Fig. 1;'and

Fig. 3 is a sectional view of one of the electric resistance probes used in the warning system.

Referring to the drawings, in the example illustrated, the improved alarm or warning system is shown installed in connection with an overhead sprinkler system of the dry pipe type. In a dry pipe sprinkler system water under pressure is always available by way of a conduit or pipe line, such as that illustrated at 10 in Fig. 2, and one or more risers 11, having a series of branch conduits 12, P13, .14 and 15 leading off therefrom into the space or spaces to be serviced, which consistof a basement head pipe lines .are usually mounted in or suspended.

from the ceiling of the room and are provided with sprinkler heads incorporating fuse plugs, which when subjected to a high temperature, melt and release air trapped under pressure in the pipes. When this occurs, the pressure in this portion of the system drops and re-. leases a dry pipe valve 1 6, which is. maintained closed as long as predetermined pressure ditterential exists thereacross but which opens when such differential drops to a certain value. Such valves may be purchased in the open market, and since their construction is Well understood in the art and form no part of the present invention, the valve is not shown in detail. Preferably, but not necessarily, the overhead pipe lines 12, 13, 14 and -15 are provided with traps 17, 18 and 19, so designed that in the event of flooding of the riser pipe =11 due to leaking of valve 16, air will be trapped in said trap-s and prevent the water from flowing into the sprinkler pipes 12, 13, 14 and .15.

The alarm system with which the present invention is primarily concerned incorporates a probe, generally indicated at 20, which is installed in each overhead pipe linedownstream of the traps 17, 18 and 19 and upstream of the sprinkler heads. One of these probes is shown in enlarged section in Fig. 3. It comprises an outer metal body 21, having a threaded shank 22, screwed into a suitable internally threaded opening formed in the pipe or conduit in which it is to be installed, which in Fig. 3 is the pipe 12, the shank being continued in the form of a tubular probe shell 23. A ceramic conducting element 24 is disposed substantially centrally within the probe shell 23 and has connected to the upper end thereof an resistance brought about by a combination of sintered' metallic oxides, suitably intermixed and in proper proportion to give the desired characteristicsysee'for.example- U. S. Patent No. 2,590,894 to Sanborn. The probe body and coacting parts which support the thermistor 24' in the manner shown constitutes an assembly-of the type disclosed and claimed in the copending application of Warren J. Gore, Serial Number 358,730, filed June 1, 1953v (common assignee). The lead Wire 25 is suitably insulated and at its upper end is brought out through a terminal 26 and anchored to the latter, the said terminal being carried by an insulating member 27, secured in an aperture formed in the upper enlarged head portion of the body 21. Offset from the terminal 26 and suitably aflixed to the adjacent portion of the body 21 is another terminal 28. The metallic part of the body of the probe, including the probe tube or. shell 23, the head of the body 21 and the shank 22, are preferably comprised of stainless steel or like material having a relatively low rate of thermal conductivity, at the same time possessinga relatively high degree of'emissivity. The member indicated at 29 is a plug to facilitate proper assembling. of the thermistor Within the probe body; it may also be made of stainless steel or like material having low thermalconducting properties, to minimize the dissipation of heat from the thermistor element 24 through the surrounding wall of the probe tube 23, to the exterior of the probe body.

The sensing element or thermistor 24 never reaches zero conductivity, and it will therefore be selfrheated as a consequence of the current flowing therethrougli; its degree of electrical conductivity is a function of "temperature and, at a constant potential, increases proportionately as its temperature increases. In the particular installation in Fig. 3, Where the air, Which 'acts as an insulator, is substantially static in the region of 'the probe tubeor shell 23, there is a relatively low-rate transfer of' heat by conduction from the tube or shell 23"to a point exteriorly of the probe, or to the wall of the pipe I2, while, at the same time there is a certain rate of transfer of'heat from the thermistor element 24 to the surrounding metali wall of the probe tube 23 which is compensated for by the generation of heat in the element. Howevenshould the probe tube 23 become submerged in wateror other fluid having good heat conducting properties, an unbal ancing action will occur and the temperature of the thermistor will lower, assuming a given potential, due to the fact that heat will be conducted from the thermistor through the probe 29-and the probe tube or shell-23 to the wall of the pipe 12 at a rate greater than the rate of self-generation. By selecting a thermistor and-associated probe shell having the proper electrical resistance and heat conducting and dissipation properties, and by im= pressingupon the conducting element-25 a voltage of a. calculated value, or Within a predetermined range; of values, thethermistor will maintain sufficient fiow of current through its associated circuit to illuminate a.visual' signal, such as a lamp, or to energize a low-voltage audible. signal.

water through the pipe 12, the heat being constantly generated due to flow of current through the thermistor. will be conducted away from the thermistor at a rate exceeding the rate of heating due to current flowing, and' the resistance of the thermistor will increase to a' point Where temperature, and even though the water'may vary in term Under such-conditions, should there be.-a*flow of 1 per-ature between, for example, 40 to F. If found desirable or necessary, the pipes 1215 may be insulated, or may be made of a material having predetermined heat insulating and/ or reflecting properties.

The electrical circuit for the probes 20 is preferably wired in a manner such as to indicate to a watchman or other attendant at a point remote from the building in which the fire extinguishing system is installed, just which partof theentire system has become activated, so that the attendant will be apprised, at aglance at a signal panel or board, of the exact location of the fire.

The supply voltage is stepped down from the main line voltage-bye suitable transformer 31, Fig. 1, and the voltage may be furtber'stepped' down by means of additional low-voltage bell ringing or signal transformers 32 and 33. One terminal of each probe, for example the terminal 28, is connected to one of the secondary terminals of its coacting signal transformer by wire 34, having interposed thereina suitably calibrated adjustable resistance in the form of 'a potentiometer35 provided with adjustable contact 36; the opposite terminal 26' of each probe being connectedby'wire 37 to the opposite terminal of said primary by way of parallel resistances shown'in the form of potentiometers 38, 39- and 40 and selecting switch contact-41 The probes when connected in this manner may beadjusted' as to the proper value of current by selecting one of the resistances 38, 39'or 40 and then adjusting the contact 36 of potentiometer 35; Thus, for example, the switch 41' may constitute a seasonal setting as, for example,- for fall and'spring, summer, and winter, while the potentiometer 35 may be utilized as amicro setting either independently or inconjunctionwith-the setting of switch 41; A suitableterminalboard is indicated at 45.

In Fig. 2 atypical signal panel is indicated at 46; it bears a plurality of signal lights, 47, 48', 49, 50, 51 and 52,"Whlll correspondto-the different floors or areas in which: the sprinkler heads'are installed. The-signals as shown in Fig.- 2 are of the-visual'type, preferably in the formof suitable low-wattlight bulbs which'remain illumin'ated' or energized as long as the current flowing through the respective thermistorelements is within a' given value, but shouldthe currentdrop below such value,

thenthe'bulbor bulbsin thethermistor circuit-will be 7 come extinguishedf Additionally, any number of audible signalsmay beemployed, such as alarm bells as indicated at-53; 54" and 55, which may be'interposed in any one or all-of therespective circuits-and be operated -bynormally-"open'relays having the proper voltage and current characteristics;

The connections indicated at-56rnay lead to a suitable storagewarehouse or other location which is more or lessremote-from the installationshown in Fig. 2. These connections are simply to illustrate how a plant or storage area may-be serviced from one panel board simply by installing suitable Wiring.

The alarm indicatedin block diagram at 57 may extend "to acity or other local fire department and'is adapted to be operated upon release of'the dry pipe valve 16. Such alarms are sometir'nesprovided as an added safety measure.

Operation beyond the dry-pipe release valve 16 has air trapped therein due to flooding of the feeder line 11, or it may be deliberately charged with a suitable gas or air at some predetermined pressure, so as to obtain the proper differential'pressure values across thevalve 16. Under such conditions, should a fire occur in theregion of any of the sprinklerheads', or 'shouldthe temperature in such region increase to some predeterminedvalue, the fuse plugs with whicli'tfidsaid sprinkler heads are provided will melt and release the air so trapped, whereupon the pressure downstream of the valve 16 will drop and the valve will open, flooding the branch pipe or pipes from which the air has been released.

As the water flows into the pipes around any one or more of the probes 20, the temperature which is being constantly generated by the flow of current through the thermistor element 24 drops, due to the conduction of heat from the probe to the surrounding walls of the pipe in the manner hereinbefore described, whereupon the resistance of the probe increases to a value such as to cause any one or more of the signal lights to become extinguished, and/ or cause any one of the audible signals to sound an alarm, thereby apprising an attendant of the exact location of the fire.

It will be obvious that the improved warning system not only functions as an alarm in case of a fire or high temperature condition, but an attendant or watchman will also be apprised should a leakage develop in any of the sprinkler head pipes and associated feeders beyond the dry pipe valve or the sprinkler heads themselves, assuming such leakage becomes such as will cause the dry-pipe valve to open and flood the normally dry piping system.

In the case of a wet type sprinkler system, i. e. one wherein the water or extinguishing fluid is constantly being maintained in all branches of the system, or at least in that branch including the pipe in which the probe is mounted, the same general type of probe may be used as in a dry system; however it may be necessary to impress a higher voltage on the thermistor in order to maintain an equilibrium resistance vs. temperature condition when the water is static, since the transfer of heat may then be somewhat greater than in a dry pipe system. However, when water begins to flow, the transfer of heat will be greatly expedited and the resultant temperature drop will reduce the resistance value of the thermistor sufficiently to energize or deenergize an associated signal.

The warning system may be wired and maintained in operation at a relatively low cost since it is of the low voltage type, while at the same time the probes involve no moving parts and will remain in proper working condition over long periods of idleness. However, should any one or more of the probes fail in a direction tend to increase the resistance of the thermistor, the associated signal or signals will become energized and warn an attendant of the failure and approximate location of the defective probe.

While only one embodiment of the invention is illustrated in the drawings, yet the disclosure is fully adequate to teach those having a knowledge of the art the principles of construction and operation and also how to adapt the invention to different installations without departing from the spirit and scope of the invention as defined by the appended claims.

What is claimed and desired to be secured by United States Letters Patent is:

1. For use with a fire extinguishing system utilizing fluid such as water as a fire extinguishing medium, a main supply conduit, a plurality of branch conduits leading off from said supply conduit into the areas to be protected, said branch conduits being provided with normally sealed sprinkler heads which when subjected to high temperatures automatically open and release the extinguishing fluid to an ignited area, probes projecting into said branch conduits each incorporating an electrical-conducting element having a high negative coeflicient of resistance and a probe tube sealing said probe from contact with the extinguishing fluid, warning signals adapted to respond to variations in current flow as determined by the resistance of said elements, an electrical circuit interconnecting said elements and said signals, and means incorporated in said circuit for selectively adjusting the value of the current flowing through said elements.

2. For use with a fire extinguishing system utilizing fluid such as water as a fire extinguishing medium, a main supply conduit, a plurality of branch conduits leading off from said supply conduit into the areas to be protected, said branch conduits being provided with normally sealed sprinkler heads which when subjected to high temperatures automatically open and release the extinguishing fluid to an ignited area or areas; probes projecting into said branch conduits each comprising an electrical-conducting element having a high negative temperature coefiicient of resistance and a probe tube surrounding said element and sealing the latter from contact with the fire extinguishing fluid, said tube having walls of low thermal conductivity and high heat emissivity; warning signals adapted to respond to variations in current flow as determined by the resistance of said elements, an electrical circuit interconnecting said elements and said signals, said electrical circuit comprising a main supply source and a plurality of individual circuits for each electrical-conducting element operatively connected to said main supply, each of said circuits being provided with a plurality of resistances of different values and selectively operable switch means connected to said source and movable to engage a selected resistance for adjusting the value of the current flowing through said elements, and an adjustable resistance common to said plurality of resistances for obtaining a finer adjustment of current flow when a given resistance has been selected.

References Cited in the file of this patent UNITED STATES PATENTS 1,869,201 Lowe July 26, 1932 2,456,617 Burch Dec. 21, 1948 2,468,676 Liben Apr. 26, 1949 2,543,588 Nelson Feb. 27, 1951 2,553,603 Peters May 22, 1951 2,602,848 Sebastian et a1. July 8, 1952

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