GB2325018A

GB2325018A - Fire alarm transducer housing

Info

Publication number: GB2325018A
Application number: GB9709111A
Authority: GB
Inventors: Manhar Amlani
Original assignee: RAFIKI PROTECTION Ltd
Current assignee: RAFIKI PROTECTION Ltd
Priority date: 1997-05-07
Filing date: 1997-05-07
Publication date: 1998-11-11
Anticipated expiration: 2017-05-07
Also published as: GB9709111D0; GB2325018B

Abstract

A housing for a fire alarm transducer 10 comprises a base 11 and a removable head 12 rotatably mounted to the base 11. A locking projection 17 projects from the base and prevents the head from being rotated, so that the head is difficult to remove by hand. A tool 20 is provided for removing the head 12. The tool 20 comprises a cup-shaped body 21 and an elongate handle 22. The upper edge of the peripheral wall of the cup-shaped body 21 comprises castellations 23 defined by axially extending slots 24, spaced at intervals around the wall. The spacing of the slots 24 in the tool 20 corresponds with the spacing of fins 14 disposed around an annular opening 13 in the head 12 of the transducer 10. The head 12 can be removed by engaging the castellations 23 of the tool with the fins 14 around the opening 13 and then rotating the tool 20 in the counter-clockwise direction. The tool 20 depresses the locking projection 17, thereby allowing the head 12 to turn. The tool 20 supports the head 12 once it has been removed, so the head 12 can be lowered away from the ceiling.

Description

Housings This invention relates to housings and more particularly, but not solely, to housings for a fire alarm transducer.

Fire alarm systems generally comprise a plurality of detectors and sounders connected to respective circuits which extend from a control panel. In use, the control panel monitors the detector circuit and applies an alarm voltage to the sounder circuit when a fire is detected.

Detectors and sounders for fire alarms typically comprise a base for fitting to the ceiling and a removable head. This arrangement simplifies installation and enables the head to be removed for cleaning or repair.

A disadvantage of providing sounders with removable heads is that people may tamper with them and remove their heads. Thus, in the event of a fire there is a risk that one or more of the sounders will not work, owing to their heads being removed. In order to overcome this problem, there is a requirement that the heads of sounders must lock to their bases.

Hitherto, the heads of sounders have been locked to their bases by means of screws, which must be removed before the head can be removed. The screws are an effective way of stopping idle or inadvertent tampering with the sounders, although they are not designed to provide any kind of permanent security.

A disadvantage of sounders is that they are often mounted on a ceiling where they are difficult to reach, without the aid of a ladder. It is often difficult to provide a ladder in the event that a sounder head has to be removed.

Furthermore, the risk of falling off the ladder is increased if a screw is provided on the sounder, because of the difficulties involved in having to remove the screw whilst holding onto the ladder.

We have now devised a housing which alleviates the above-mentioned problems.

In accordance with this invention as seen from a first aspect, there is provided a housing having a base and a head detachably mounted to the base and having a formation thereon for engagement by a head removal tool, and locking means for locking the head to the base, the locking means being positioned such that the head is unlocked from the base when the head removal tool is engaged with said formation.

In use, when the tool is engaged with the head of the housing, it actuates the locking means to unlock the head from the base. The locking arrangement is thus much simpler to unlock than conventional locking means, although it is just as effective at preventing the head from being removed when the housing is tampered with.

Preferably the base comprises a planar surface for mounting against a ceiling or other flat surface, the locking means being disposed below said surface on a line which extends perpendicular to said planar surface, the locking means being exposed in a direction which extends along said line, away from said surface. The locking means is thus accessible by a tool raised from below.

Preferably the formation comprises a socket.

Preferably the locking means is mounted in said socket.

Preferably the head is rotatably mounted to the base, the locking means being arranged to prevent rotation of the head in a removal direction.

Preferably a plurality of formations are provided on the head for engagement by the tool, the formations being arranged around the axis of rotation of the head.

Preferably the locking means comprises a projection on the base, and means for biasing the projection into a locked position. When the tool is engaged with the housing, it abuts the projection and moves it into its unlocked position, whereupon the head can be removed.

Also, in accordance with this invention as seen from a second aspect, there is provided a housing in combination with a tool for removing a head of the housing, the head being detachably mounted to a base of the housing, the housing comprising locking means which locks the head to the base, the tool comprising a body having means for engaging the head and means for moving the locking means from its locked to its unlocked position, in which the head can be removed from the base.

Preferably the tool comprises an elongate handle, so that it can be engaged with a housing on the ceiling without the aid of a ladder.

Preferably the tool is arranged to support the head when the head is detached from the body.

Preferably the head comprises means for engaging the body, the engagement means being operable by movement of the head relative to the base.

Preferably the head is rotatably mounted to the base, the head being rotatable between a position in which it is unlocked from the base and a position in which it is locked to the base.

Preferably the tool and head comprise complementary engaging formations, which enable the head to be moved relative to the body in order to engage or disengage it from the base.

Preferably the formation on the head comprises a socket, the locking means being disposed in said socket.

An embodiment of this invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a fire alarm transducer in accordance with this invention, together with a head removal tool; Figure 2 is a side view of the transducer of Figure 1; Figure 3 is a fragmentary sectional view along the line III-III of Figure 2; Figure 4 is a fragmentary sectional view along the line IV-IV of Figure 3; Figure 5 is a perspective view of the head removal tool of Figure 1, when engaged with the transducer; Figure 6 is a side view of the head removal tool of Figure 1, when engaged with the transducer; Figure 7 is a fragmentary sectional view along the line VII-VII of Figure 6; and Figure 8 is a fragmentary sectional view along the line VIII-VIII of Figure 7.

Referring to Figures 1 to 4 of the drawings, there is shown a dome-shaped fire alarm transducer 10, comprising a base 11 and a removable head 12. An annular peripheral opening 13 is disposed between the head 12 and the base 11, the head 12 carrying radially extending fins 14, which extend over the mouth of the opening 13 to form a barrier across the opening.

The base 11 comprises an external housing 18 having a planar upper surface for fixing to the ceiling, and a removable internal housing 16 having a flat lower surface, which forms the roof of the opening 13. A printed circuit board (not shown) is mounted in the internal housing 16 of the base 11 and is connected to the alarm control panel via one or more cables which extend through the ceiling. An audible warning transducer and heat and smoke sensors are also mounted on the printed circuit board, and are arranged so that sound is emitted through the opening 13 and so that smoke and heat can reach the respective sensors through the opening 13.

An annular channel 19 is formed between the internal housing 16 of the base 11 and the peripheral wall of its external housing 18, as shown in Figure 3. An annular wall 15 is connected at its lower edge to the outer edge of the upper surface of the fins 14. L-shaped slots e.g. 30 are formed at intervals around the annular wall 15 of the head 12, as shown in Figure 2, the L-shaped slots 30 having an axially-extending portion which extends downwardly from the upper edge of the wall 15 and a circumferentially-extending portion which extends from the bottom of the axially-extending portion in the counter-clockwise direction (when viewed from below). Pegs (not shown) project radially into the annular channel 19 in the base 11 from the peripheral wall of the external housing 18.

The annular wall 15 of the head 12 extends into the annular channel 19 in the base 11 and the head 12 is held in engagement with the base 11, because the pegs on the base 11 extend into the circumferentially extending portions of respective L-shaped slots 30 in the annular wall 15 of the head 12.

The head 12 comprises a dome-shaped cover 34 which coextends with the outer end surface of the fins 14 and with the surface of the peripheral wall of the base 10. The diameter of the opening 13 is greater across its roof than across its base. A locking projection 17 projects downwardly from the lower surface of the internal housing 16 of the base 10 (which defines the roof of the opening 13) into the opening 13, at a point which is located radially outwardly of the edge of the floor of the opening 13. Thus, it will be appreciated that the projection 17 is visible on the roof of the opening 13, when viewed from below.

The internal housing 16 of the base 11 is manufactured by injection moulding from plastics material. The projection 17 comprises a triangular-shaped pawl which is moulded as one piece with the bottom wall of the internal housing 16, and which is attached thereto by a resiliently flexible plastics web 31, as shown in Figure 4. The projection 17 comprises an abutment surface 32 and an inclined lower surface 33, extending between the lower edge of the abutment surface 32 and the resiliently flexible web 31. The abutment surface 32 lies in a plane which extends radially of the transducer 10.

In its as-moulded condition, the projection 17 projects below the lower surface of the internal housing 16, the abutment surface extending perpendicular to the plane of the lower surface. When the head is turned in the counterclockwise direction (i.e. in the removal direction), one of the fins 14 thereon abuts the abutment surface 32 of the projection, thereby preventing further rotation of the head.

The head removal tool 20 comprises a cup-shaped body 21 having a circular base and an upstanding annular peripheral wall. The upper edge of the peripheral wall comprises castellations 23 defined by axially extending slots 24, spaced at intervals around the wall. An elongate handle 22 extends from the underside of the base.

The internal diameter of the cup-shaped body 21 of the tool 20 is slightly greater than the diameter of the floor of the opening 13 in the alarm transducer 10 but less than the diameter of the roof of the opening 13. The depth of the cupshaped body 21 of the tool 20 is greater than the distance from the roof of the opening 13 in the transducer 10 to the underside of the head 12 thereof.

The spacing of the slots 24 in the tool 20 corresponds with the spacing of the fins 14 around the opening 13 in the transducer 10. The width of the slots 24 is greater than the thickness of the fins 14. The length of the slots 14 is greater than the height of the opening 13.

Referring to Figures 5 to 8 of the drawings, in order to remove the head 12 of the transducer 10, the body 21 of the tool 20 is raised to the ceiling using the elongate handle 22.

The tool 20 is then rotated until the slots 24 in its body 21 align with the fins 14 on the transducer 10, whereupon the tool 20 is engaged with the transducer 10 by moving it axially, to cause the castellations 23 thereon to enter respective sectors of the opening 13 between adjacent fins 14. The upper edge of one of the castellations 24 presses against the projection 17 and presses it flush with the lower surface of the internal housing 16 of the base 11, as shown in Figures 7 and 8.

The tool 20 is then rotated in the counter-clockwise direction, as shown in Figure 5, thereby rotating the head 12 of the transducer 10 relative to its base 11: it will be appreciated that the depressed projection 17 no longer abuts one of the fins 14 to prevent rotation of the head 12. The head 12 can now be removed from the base 11 by lowering the tool 20 away from the ceiling, the tool serving to support the head.

In order to replace the head 12 of the transducer 10, say once maintenance or cleaning has been carried out, the head is inserted into the cup-shaped body 21 of the tool, and raised up to the base 11 of the transducer 10, which is still disposed on the ceiling. The L-shaped slots 30 in the annular wall 15 of the head 10 are aligned with respective pegs on the base 11, whereupon the annular wall 15 of the head 12 is able to fully enter the annular cavity 19 in the base 11. In this position, the tool 20 depresses the projection 17, and the head 12 is then engaged with the base 11 by turning the head in the clockwise direction, so that the pegs enter the circumferentially-extending portion of their respective Lshaped slots 30.

When the tool 20 is removed, the projection 17 is biassed downwardly into the opening, in order to lock the head 12 against rotation in the counter-clockwise direction. It is possible to also lock the head 12 to the base 11 without the tool, simply by inserting the head and turning it in the clockwise direction as before. As the head is turned, the fins 14 ride over the inclined surface 33 of the projection 17, thereby depressing it until the head has rotated to its engaged position, whereupon the projection 17 snaps downwardly into its locked position.

The head 12 can be removed without the tool 20, by depressing the projection, say with a screwdriver, whilst simultaneously turning the head 12. However, the lock that is provided between the head 12 and the base 11 is sufficient to prevent the head from being removed by people who idly tamper with the transducer.

In an alternative embodiment, a plurality of projections may be disposed at intervals around the transducer, thereby making it more difficult to remove the head without the tool.

Claims

1) A housing having a base and a head detachably mounted to the base and having a formation thereon for engagement by a head removal tool, and locking means for locking the head to the base, the locking means being positioned such that the head is unlocked from the base when the head removal tool is engaged with said formation.

2) A housing as claimed in claim 1, in which the base comprises a planar surface for mounting against a ceiling or other flat surface, the locking means being disposed below said surface on a line which extends perpendicular to said planar surface, the locking means being exposed in a direction which extends along said line, away from said surface.the formation comprises a socket.

3) A housing as claimed in claims 1 or 2, in which the locking means is mounted in said socket.

4) A housing as claimed in any preceding claim, in which the head is rotatably mounted to the base, the locking means being arranged to prevent rotation of the head in a removal direction.

5) A housing as claimed in claim 4, in which a plurality of formations are provided on the head for engagement by the tool, the formations being arranged around the axis of rotation of the head.

6) A housing as claimed in any preceding claim, in which the locking means comprises a projection on the base and means for biasing the projection into a locked position.

7) A housing substantially as herein described with reference to the accompanying drawings.

8) A housing in combination with a tool for removing a head of the housing, the head being detachably mounted to a base of the housing, the housing comprising locking means which locks the head to the base, the tool comprising a body having means for engaging the head and means for moving the locking means from its locked to its unlocked position, in which the head can be removed from the base.

9) A housing as claimed in claim 8, in which the tool comprises an elongate handle.

10) A housing as claimed in claims 8 or 9, in which the tool is arranged to support the head when the head is detached from the body.

11) A housing as claimed in any of claims 8 to 10, in which the head comprises means for engaging the body, the engagement means being operable by movement of the head relative to the base.

12) A housing as claimed in any of claims 8 to 11, in which the head is rotatably mounted to the base, the head being rotatable between a position in which it is unlocked from the base and a position in which it is locked to the base.

13) A housing as claimed in any of claims 8 to 12, in which the tool and head comprise complementary engaging formations, which enable the head to be moved relative to the body in order to engage or disengage it from the base.

14) A housing as claimed in any of claim 13, in which the formation on the head comprises a socket, the locking means being disposed in said socket.

15) A tool for removing a head of a housing, the tool being substantially as herein described with reference to Figures 1,5,6,7 and 8 of the accompanying drawings.