GB2270840A - A triggering arrangement for a fire safety device - Google Patents

Abstract

A triggering arrangement for a fire safety device such as a fire damper or a sprinkler system comprises means for retaining the device in an inoperative condition, with the retaining means being movable so as to enable the device to adopt an operative condition. The arrangement incorporates a thermal sensor associated with the retaining means, the thermal sensor comprising a plurality of discrete substantially identical frangible components ie. frangible bulbs (8) designed to break at a temperature in excess of a predetermined temperature. The arrangement is designed so that the retaining means enable the fire safety device to adopt the operative condition in response to the breaking of any one of the frangible components. <IMAGE>

Description

DESCRIPTION OF INVENTION A Triggering Arrangement for a Fire Safety Device.

THE PRESENT INVENTION relates to a triggering arrangement for a fire safety device such as a fire damper.

A fire damper is a component which is mounted within ducting in a heating, ventilating or air conditioning system and which serves, in the event of a fire, to form a barrier within the ducting so as to prevent a fire from spreading from one part of a building to another via the ducting of the heating, ventilating or air conditioning unit. The damper may, for example, comprise a series of blades mounted within a peripheral frame which is in turn mounted within the ducting, the blades being pivotally mounted for movement between an open position in which air may flow through the damper and a closed position in which the damper forms a physical barrier closing off the ducting. The edges of the blades may be provided with seals or formed in such a way that the damper also serves as a barrier against the spread of smoke through the ducting.

The damper is normally held in the open position and incorporates a triggering arrangement which responds to a fire situation and releases the damper from the open position so that it can move to the closed position.

It has previously been proposed to provide a triggering arrangement for a fire damper which incorporates a frangible glass bulb filled with liquid. The frangible bulb acts as a sensor in that the liquid within the bulb expands as the ambient temperature increases until eventually the glass bulb fractures. Bulbs of this nature are available which will fracture at a predetermined temperature. Thus, this type of bulb can form part of the means which normally retain a fire damper in the open position, with the triggering arrangement being such that the bulb will fracture at a given temperature whereupon the damper will automatically move to the closed position.

Problems have been experienced in connection with damper triggering arrangements incorporating a frangible bulb of the type discussed above in that, on occasions, the bulb has not fractured when it should. Thus, in some cases the bulb did not fracture for up to twenty minutes after a fire situation had developed.

In order to address this problem it is known to provide a second, independent triggering arrangement which should release the fire damper if the frangible bulb does not fracture when it should. Thus, it is known to provide a triggering arrangement which incorporates a frangible bulb and a separate fusible link or some other different form of sensor. Clearly this is a relatively costly arrangement and care must be taken to ensure that the damper will move to the closed position in the event of either of the sensors detecting a fire situation.

The present invention seeks to provide an improved triggering arrangement for a fire safety device which is cost effective to produce and install and which is reliable in operation.

According to one aspect of this invention there is provided a triggering arrangement for a fire safety device, the arrangement comprising means for retaining the device in an inoperative condition, the retaining means being movable between a first position corresponding to said inoperative condition and second position corresponding to an operative condition of the device; and a thermal sensor associated with the retaining means, the thermal sensor comprising a plurality of a discrete, substantially identical frangible components designed to break at a temperature in excess of a predetermined temperature, the arrangement being such that the retaining means move from said first position to said second position in response to breaking of any one of the frangible components.

Preferably the frangible components are serially connected.

Conveniently the retaining means comprise an elongate, axially movable element which cooperates with part of the fire safety device when in use.

Advantageously the elongate axially movable element is biassed to said second position corresponding to an operative condition of the fire safety device.

Preferably the elongate axially movable element comprises a plurality of abutting sections and the frangible components constitute sections of the element.

Conveniently the elongate axially movable element is accommodated within a tube.

Advantageously the tube defines windows at positions corresponding to the location of the frangible components within the tube.

The frangible components may comprise liquid-filled glass bulbs.

The arrangement may incorporate two or three frangible components.

This invention also provides a fire safety device incorporating a triggering arrangement as described above.

The fire safety device may comprise a fire damper or a sprinkler system.

In order that the present invention may be more readily understood and so that further features thereof may be appreciated, the invention will now be described by way of example, with reference to the accompanying drawings in which: FIGURE 1 is a partly sectioned general assembly drawing of a triggering arrangement in accordance with this invention; FIGURE 2 is a view corresponding to Figure 1 but showing a modified arrangement of the same design; and FIGURE 3 is also a partly sectioned general assembly drawing of a further embodiment of a triggering arrangement in accordance with this invention.

The drawings illustrate triggering arrangements designed for use with a fire damper and reference numeral 1 identifies part of the damper casing. The casing is formed with a circular aperture 2 through which the triggering arrangement extends. A nut 3 is secured on one side of the damper casing 1 so that its threaded passage is aligned with the aperture 2 in the casing.

The triggering arrangement itself comprises an outer tube 4 formed of stainless steel, the tube being formed with windows 5 at two locations along its length.

One end of the tube 4 is externally threaded over a short length, as shown by reference numeral 6. The other end of the tube 4 is provided with a plug 7 in the form of a smaller tube which is welded inside the outer tube 4.

Thus, although referred to as a plug, the component 7 does not in fact close off the end of the tube 4.

The outer tube 4 is dimensioned so that a liquid-filled frangible glass bulb 8 may be slid into the tube from the threaded end thereof so that it engages and is held in the tube by the plug 7. The bulb 8 is a conventional 'sprinkler bulb' which is available from Day-Impex Limited of Colchester, Essex, England. The glass bulb is designed to fracture and break at a predetermined temperature due to the expansion of the liquid contained within the bulb.

Behind the bulb 8 a connecting tube 9 is received within the outer tube 4, the connecting tube being dimensioned so that it just passes down the inside of the outer tube 4 with a very small clearance. A second liquid-filled frangible glass bulb 8 is located within the outer tube 4 behind the connecting tube 9. The glass bulbs 8 are aligned with the windows 5 formed in the outer tube 4 when they are inserted into the outer tube in the manner described above and as shown in the drawings.

Behind the second glass bulb 8 the outer tube 4 accommodates a stainless steel shaft 10 which extends out of the threaded end of the tube 4. The end of the shaft 10 which engages the second glass bulb 8 is formed with a short central bore 11 so that a circular seat is defined at the end of the shaft which engages the glass bulb 8. The free end of the shaft 10 which is located outside of the tube 4 has a portion which is of reduced cross-section, as identified by reference numeral 11, there being a ring or collar 13 at the junction between the reduced-section portion 12 and the remainder of the shaft 10. A compression spring 14 surrounds the reduced section portion 12 of the shaft and seats upon the collar 13.

-The triggering arrangement is primed by means of a component 15 in the form of a bolt which passes over the reduced section end 12 of the shaft 10 and serves to compress the spring 14. The bolt 15 is formed from stainless steel and has a head 16 and a externally threaded shank 17. A small bore 18, through which the reduced section 12 of the shaft 10 just passes, extends through the head 16 of the bolt into an enlarged bore 19 which extends over the full length of the shank 17. The bore 19 is internally threaded over part of its length from the free end of the shank of the bolt. This internal threading at the end of the bore 19 enables the bolt 15 to be connected to the externally threaded end 6 of the outer tube 4. The bore 19 is dimensioned to receive the spring 14 whilst the smaller bore 18 will not.Thus the end of the bore 19, from which the bore 18 extends, engages the end of the spring 14 remote from the collar 13.

The triggering arrangement is assembled by initially sliding the first frangible bulb 8 down inside the outer tube 4 so that it engages the plug 7 and is aligned with the windows 5. The connecting tube 9 is then slid down inside the outer tube 4 so that it engages the rear of the first frangible bulb 8. The second frangible bulb 8 is then slid down the outer tube 4 until it engages the connecting tube 9, the length of which automatically ensures that the second bulb 8 is aligned with the second windows 5 formed in the outer tube. The shaft 10 is then inserted into the end of the tube 4 until its end engages the rear of the second frangible bulb 8. The spring 14 is located over the reduced section part of the shaft 10 so that it seats against the collar 13.The bolt 15 is then passed over the reduced-sectioned end 12 of the shaft 10 so that the reduced section 12 passes through the bore 18 in the head of the bolt and projects therefrom. The bolt 15 is connected to the outer tube 4 by the cooperating screw threads on the exterior of the tube and the interior of the bolt, thereby compressing the spring 14 so that the shaft 10 is biassed to the left as viewed in Figure 1 of the drawings. The triggering arrangement is now primed and can be connected to a fire damper by screwing the bolt 15 into the nut 3 mounted on the damper casing 1 so that the portion of the outer tube 4 which accommodates the frangible glass bulbs 8 is disposed on one side of the casing whilst the reduced section end 12 of the shaft 10 is disposed on the other side of the case.

It will be appreciated that when the triggering arrangement is mounted in place the frangible bulbs 8 are exposed to air flowing through the duct or the like in which the damper is mounted and if the temperature increases the liquid within the glass bulbs 8 will expand until, at a predetermined temperature, the bulbs should fracture and break. When this happens the spring 14 causes the shaft 10 to move to the left (as viewed in the drawings) so that the reduced section end of the shaft is drawn into the bolt 15. This movement of the shaft activates closure of the damper. In Figure 1 of the drawings a switch 20 has been illustrated in outline with the free end of the reduced section 12 of the shaft engaging the switch 20 through an intermediate component 21.When the triggering arrangement responds to a temperature in excess of a predetermined limit and the shaft 10 moves to the left the switch 20 which controls activation of the damper is disengaged. It should be appreciated that activation of the damper could be effected by any appropriate means connected to the triggering arrangement of this invention.

It will be appreciated that the arrangement described above and illustrated in Figure 1 of the drawings will trigger activation of the damper if either one of the glass bulbs 8 fracture. Thus, if the first frangible bulb 8 which is located adjacent the end plug 7 fractures then the spring 14 will cause not only the shaft 10 to move to the left but will also cause the second frangible bulb 8 and the connecting tube 9 to move to the left.

Alternatively if the second frangible bulb 8 is the first bulb to fracture then the first frangible bulb and the connecting tube 9 will remain in place and only the shaft 10 will be moved to the left under the action of the spring 14. In any event if one of the frangible bulbs 8 is sub-standard and does not fracture when it should then the arrangement should still trigger closure of the damper when the other frangible bulb fractures. Thus the arrangement of this invention is far more reliable than one which incorporates a single frangible bulb. It is also far less expensive than providing two different, independent triggering systems, both of which will require assembly and priming.

Figure 2 of the drawings illustrates a slightly modified version of the Figure 1 arrangement. In the design of Figure 2 the triggering arrangement incorporates three liquid-filled frangible glass bulbs 8 instead of two, there being an additional connecting tube 9 extending between the second and third frangible bulbs within the outer tube 4. In all other respects the embodiment of Figure 2 is identical to that of Figure 1 and will therefore not be described again. Providing a third frangible bulb 8 further increases the reliability of the triggering arrangement.

Figure 3 of the drawings shows an arrangement where two frangible bulbs are disposed in parallel rather than in series as they are in the embodiment of Figure 1. In the schematic illustration of Figure 3 the damper casing is again identified by the reference numeral 1 and this casing defines an aperture 2 through which the triggering arrangement passes. The arrangement comprises a shaft 22, one end of which engages a switch 20 through an intermediate component 21 in the same way as was described in connection with Figures 1 and 2. The other end of the shaft 23, which passes through the aperture 2 in the damper casing, is pivotally connected at a point 24 to an arm 25, the opposed ends of which each engage a liquid-filled frangible glass bulb 26 which is supported between a surface 27 and the pivotally mounted arm 25. The surface 27 may be constituted by a component which is fixed to the damper casing 1 or which is fixed within the ducting in which the damper is mounted. On that side of the casing 1 where the frangible bulbs 26 are located the shaft 23 carries a ring or collar 28 and a spring 29 extends between this, and the damper casing surrounding the shaft 23. Thus, the spring 29 biasses the shaft 23 and the arm 25 which is carried thereby towards the left in Figure 3 of the drawings.

In order to prime the triggering arrangement of Figure 3 the frangible bulbs 26 are located in position between the surface 27 and the arm 25 by compressing the spring 29 and/or pivoting the arm 25 appropriately. When primed and in situ the free end of the shaft 23 engages the switch 20 in the manner as described above. If the temperature of the air within the ducting in which the damper is mounted exceeds a predetermined limit then the bulbs should fracture allowing the shaft 23 to move to the left under the action of the spring 29 thereby operating the switch 20 which activates closure of the damper. Again it will be appreciated that the triggering arrangement will serve to close the damper in the event of either one of the bulbs 26 fracturing. Thus, when one of the bulbs fractures the arm 25 is no longer held in a balanced position and pivots about the point 24 as the spring 29 causes the shaft 23 to move to the left, so that the other bulb will automatically fall away from between the surface 27 and the arm 25.

It is to be appreciated that the illustration of Figure 3 is only schematic and the shaft 23 would probably be supported within a bush or sleeve of some sort mounted on the damper casing.

It is to be appreciated that although the invention has been described with reference to its use with a fire damper, the invention may also be used in connection with other fire safety devices such as sprinkler systems where the system is normally to be held in an inoperative condition and a triggering arrangement is required in order to activate the system in response to a fire situation.

Claims (18)

1. A triggering arrangement for a fire safety device, the arrangement comprising means for retaining the device in an inoperative condition, the retaining means being movable between a first position corresponding to said inoperative condition and second position corresponding to an operative condition of the device; and a thermal sensor associated with the retaining means, the thermal sensor comprising a plurality of a discrete, substantially identical frangible components designed to break at a temperature in excess of a predetermined temperature, the arrangement being such that the retaining means move from said first position to said second position in response to breaking of any one of the frangible components.

2. A triggering arrangement according to Claim 1 wherein the frangible components are serially connected.

3. A triggering arrangement according to Claim 1 or Claim 2 wherein the retaining means comprise an elongate, axially movable element which cooperates with part of the fire safety device when in use.

4. A triggering arrangement according to Claim 3 wherein the elongate axially movable element is biassed to said second position corresponding to an operative condition of the fire safety device.

5. A triggering arrangement according to Claim 3 or Claim 4 wherein the elongate axially movable element comprises a plurality of abutting sections and the frangible components constitute sections of the element.

6. A triggering arrangement according to Claim 3, 4 or 5 wherein the elongate axially movable element is accommodated within a tube.

7. A triggering arrangement according to Claim 6, as dependant upon Claim 5, wherein the tube defines windows at positions corresponding to the location of the frangible components within the tube.

8. A triggering arrangement according to any one of the preceding claims wherein the frangible components comprise liquid-filled glass bulbs.

9. A triggering arrangement according to any one of the preceding claims wherein the arrangement incorporates two frangible components.

10. A triggering arrangement according to any one of Claims 1 to 8 wherein the arrangement incorporates three frangible components.

11. A triggering arrangement substantially as herein described with reference to and as shown in Figure 1 of the accompanying drawings.

12. A triggering arrangement substantially as herein described with reference to and as shown in Figure 2 of the accompany drawings.

13. A triggering arrangement substantially as herein described with reference to and as shown in Figure 3 of the accompany drawings.

14. A fire safety device incorporating a triggering arrangement in accordance with any one of the preceding claims.

15. A fire safety device according to Claim 14 wherein the device comprises a fire damper.

16. A fire safety device according to Claim 14 wherein the device comprises a sprinkler system.

17. A fire safety device substantially as herein described.

18. Any novel feature or combination of features disclosed herein.