GB2189065A - Fire alarm - Google Patents

Abstract

The fire alarm comprises an audible alarm device 18, 19, 20 connectible to a source of pressurized fluid 12 through the intermediary of a normally closed valve means 13 openable at a predetermined temperature to permit fluid flow to an impulse generator 15 adapted to operate the audible alarm device. The normally closed valve means is retained closed by a fusible medium and is openable under the action of a mechanical spring. The source of pressurized air may either be a self-contained source, or a mains supply. The above components may be mounted on a backplate 10 and enclosed by the dome 20 of an alarm bell constituting the alarm device. Such bell may comprise a clanger 19 operated by a piston and cylinder device 18 which receives pressurized impulses from the generator 15. <IMAGE>

Description

SPECIFICATION Fire alarms This invention relates to fire alarms.

At present fire alarms are generally triggered either electrically, the fire alarm forming part of an electrical circuit containing a fuse which is adapted to melt at a predetermined temperature thereby rendering the electrical circuit operational and activating the fire alarm; or by water pressure, the fire alarm forming part of a sprinkler system and being operated when there is a rapid drop in water pressure within the sprinkler system which occurs when the sprinklers become operational due to the attainment of a predetermined temperature within the space to be protected by the sprinklers.

With an electrically operated fire alarm there is always the possibility of a failure in the electrical supply system with consequent nonoperation of the fire alarm if a fire occurs. In the case of a fire alarm operated by a drop in water pressure there is always the risk of a loss of water pressure within the system so that the fire alarm would not be operated in the case of a fire occuring since no drop in water pressure would occur.

A further disadvantage of both of these systems is that they are expensive to install and entail substantial construction work in their installation.

It is an object of the present invention to provide a fire alarm which obviates or mitigates the aforesaid drawbacks inherent in the known systems.

According to the present invention there is provided a fire alarm comprising an audible alarm device connectible to a source of pressurized fluid through the intermediary of a normally closed valve means openable at a predetermined temperature to permit fluid flow to an impulse generator adapted to operate the audible alarm device.

Preferably, the normally closed valve means is retained closed by a fusible medium adapted to melt on attainment of the aforesaid predetermined temperature thereby to permit the valve means to open.

Preferably, the valve means is openable under the action of a mechanical spring.

Preferably, the source of pressurized air is a self-contained source. Alternatively the source of pressurized air may be a mains supply.

Preferably, the audible alarm device is a bell, the danger of which is operated by a variable impulse generator adapted to be supplied with fluid under pressure upon opening of the valve means and to deliver pulses of air to the clanger of the alarm bell.

Preferably, the danger is operated by a piston movable under the action of the pulses of fluid.

Preferably, the fluid is air but may be any other inert gas or mixture of gases with or without the presence of air.

Preferably, the self-contained source of pressurized air, the valve means, the impulse generator and the danger are all mounted on a backplate and are enclosed under the dome of the alarm bell. The fire alarm is thus a unitary assembly which means that it can be fixed to a suitable wall in the space to be monitored for the presence of a fire. This construction allows the fire alarm not only to be used in industrial or commercial premises but also domestic premises.

The fusible medium may be a wax, solder or any other medium adapted to melt at the predetermined temperature for example 136"F (57.8"C).

Preferably, the fusible medium is in the form of a plug, the dome of the alarm bell being provided with an opening through which the melted medium can flow to allow opening of the valve means and consequent operation of the fire alarm.

Preferably, a pressure indicator is associated with the source of fluid under pressure so that a visible check can be made that there is fluid under pressure present and that it is at the desired pressure value.

As a result of the present invention there is provided a fire alarm which is simple and economic to produce and which is self-contained requiring no electrical wiring or piping other than the piping necessary to connect the aforesaid components of the fire alarm in operational circuit.

The fire alarm is relatively lightweight, is compact and is readily portable so that it can be moved from one room to another. The dome of the fire alarm may be rendered decorative so that it can blend with the decor of the room in which the fire alarm is installed.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a front view of the fire alarm with the dome omitted, the dome periphery being indicated in dot-dash iines; Figure 2 is a perspective view of the fire alarm according to the invention; and Figure 3 is a detail view of the valve means and restraining fusible medium.

Referring to the drawings of the fire alarm comprises a backplate 10 adapted to be secured to a wall by appropriate screws or bolts (not shown), holes 11 being provided in the backplate for such screws or bolts.

The fire alarm comprises a container 12 holding a supply of air under pressure, the air pressure being in excess of atmospheric pressure.

A normally closed poppet valve 13 is connected to the cylinder 12 by a pipe 14 and is connected to a variable impulse generator 15 by a pipe 16. The outlet from the variable impulse generator 15 is connected by a pipe 17 to a piston and cylinder device 18 which is adapted to operate a danger 19 to cause same to strike a dome 20 which overlies the backplate and encloses the cylinder 12, valve 13, variable impulse generator 15, piston and cylinder device 18 and danger 19 save for a central opening 21 which is normally closed as will be shortly described.

The above-described components of the fire alarm are suitably secured to the backplate 10 say by screws or any other convenient form of fastening.

The poppet valve 13 is normally held closed by a plug 22 of fusible wax or solder for example adapted to melt at a predetermined temperature. The poppet valve 13 is spring loaded to open position so that when the plug 22 melts the spring 23 of the poppet valve 13 causes same to open thus allowing pressurised air to flow from the cylinder 12 through the poppet valve 13 to the variable impulse generator 15 which delivers pulses of air to the piston and cylinder device 18 causing the clanger to strike the dome 20 at a frequency determined by the setting of the variable impulse generator 15.

The fire alarm is designed to operate within say 20 seconds of a temperature of 136"F (57.8"C) being reached in the space within which the fire alarm is located.

The fire alarm is designed to operate at a frequency known as the "killer frequency" which guarantees to alert all persons within a distance of 50 to 60 yards of the fire alarm.

The fire alarm preferably operates for at least 5 minutes.

It is preferred that the quantity of air contained within the cylinder is in excess of that required to operate the fire alarm for this minimum period of 5 minutes.

Claims (12)

1. A fire alarm comprising an audible alarm device connectible to a source of pressurized fluid through the intermediary of a normally closed valve means openable at a predetermined temperature to permit fluid flow to an impulse generator adapted to operate the audible alarm device.

2. A fire alarm as claimed in claim 1, in which, the normally closed valve means is retained closed by a fusible medium adapted to melt on attainment of the aforesaid predetermined temperature thereby to permit the valve means to open.

3. A fire alarm as claimed in claim 1 or 2, in which the valve means is openable under the action of a mechanical spring.

4. A fire alarm as claimed in any one of claims 1 to 3, in which the source of pressurized air is either a self-contained source, or mains supply.

5. A fire alarm as claimed in any one of claims 1 to 4 in which the audible alarm device is a bell, the danger of which is operated by a variable impulse generator adaptor to be supplied with fluid under pressure upon opening of the valve means to deliver pulses of air to the danger of the alarm bell.

6. A fire alarm as claimed in claim 5, in which the danger is operated by a piston movable under the action of the pulses of fluid.

7. A fire alarm as claimed is any one of claims 1 to 6, in which the fluid is air but may be any other inert gas or mixture of gases with or without the presence of air.

8. A fire alarm as claimed in any one of claims 4 to 7, in which the self-contained source of pressurized air, the valve means, the impulse generator and the danger are all mounted on a backplate and are enclosed under the dome of the alarm bell.

9. A fire alarm as claimed in any one of claims 1 to 8, in which the fusible medium is a wax, solder or any other medium adapted to melt at the predetermined temperature.

10. A fire alarm as claimed in any one of claims 1 to 9 in which the fusible medium is in the form of a plug, the dome of the alarm bell being provided with an opening through which the melted medium can flow to allow opening of the valve means and consequent operation of the fire alarm.

11. A fire alarm as claimed in any one of claims 1 to 10, in which a pressure indicator is associated with the source of fluid under pressure so that a visible check can be made that there is fluid under pressure present and that it is at the desired pressure value.

12. A fire alarm, substantially as hereinbefore described with reference to the accompanying drawing.