Latch mechanism

Details Latch mechanism Latch mechanism

2000-03-24

2001-11-20

Chambers, A. Michael (Department: 3753)

Fluid handling

Ambient condition change responsive

Atmospheric

C137S601070, C454S369000

Reexamination Certificate

active

06318399

ABSTRACT:

This invention relates to a latch mechanism for attachment to a frame of a fluid damper such as, in particular a fire or smoke shield of a ventilation system.
Fire or smoke shields used in normal dry filtered air ventilation systems generally comprise a support frame that is received in a duct of the ventilation system and a retractable curtain that is reversibly extensible between a retracted position in which the duct is open and an extended position in which the curtain closes and seals against the frame so as to damp the flow of air in the duct aid thereby hinder the progress of the fire.
Our UK patent Nos. GB 2180745, GB 2224440 and GB2223676 describe a latch mechanism that is mounted on the support frame of a fire shield, The shield comprises a multiple-blade folding curtain fire damper that, in use, is normally retracted within the support frame so as to leave the duct open. The latch has jaws that are adapted to engage a bottom edge of the curtain so as to hold it in the retracted position and includes a fusible element that melts at a predetermined temperature so as to release the jaws (and therefore the curtain) to effect closing of the duct in the event of a fire. The latch is provided with a dual fail-safe arrangement with a thermal link in the form of memory metal springs that expand at said pre-determined temperature so as to release the latch jaws.
It is important that fire shields of the kind described above are inspected and tested at regular intervals to ensure that they perform properly in the event of a fire. To reach the shield and the latch mechanism it is usual for an inspection hatch to be provided in one of the ducts adjacent the shield so that a technician can gain access to the curtain and the latch mechanism. In our aforementioned patents there is described a latch mechanism with a manually operable release mechanism that allows the technician to test operation of the latch mechanism and movement of the curtain to the extended position. There is also described a removable mounting mechanism that allows the latch to be removed and fitted with a replacement fusible element, if necessary. After inspection and/or servicing of the fire shield it is necessary for the technician to reset the curtain in the retracted position. This is often a difficult operation, as the curtain has to be held in the retracted position until the latch can be reset. It is made more difficult by the construction of the mechanism as it is easy for the technician to inadvertently reset the latch before the curtain is fully retracted by causing the curtain blades to brush against the jaws of the latch mechanism.
It is an object of the present invention to obviate or mitigate the aforementioned problems of disadvantages.
According to a first aspect of the present invention, there is provided a latch mechanism for attachment to a frame of a fluid damper, the mechanism comprising a housing having at least one latch member biased so as to project from the housing and movable between a first position in which it engages a barrier of the damper so as to hold it in a retracted position and a second position in which it is clear of the barrier so as to release the barrier from the retracted position characterised in that the at least one latch member is held in said first position by a releasable locking member, the locking member being operatively coupled to a thermally sensitive element such that when the thermally sensitive element reaches a pre-determined temperature it changes shape or state so as to release the locking member thereby allowing the latch member to move to the second position, and in that the latch member is movable against the bias to a third position in which it is retracted into the housing so as to permit movement of the barrier to the retracted position.
This arrangement simplifies the resetting procedure after the curtain has been released since the latch member is able to retract should the barrier come into contact with it as it is moved back to the retracted position.
Preferably the latch member is pivotable between first and second positions about a pin.
The locking member may be held in the unreleased state by a locking pin that engages with the locking member and is acted on by the thermally sensitive element.
The locking member may be released by virtue of expansion of the thermally sensitive element at said pre-determined temperature causing the locking pin to move out of engagement with locking member. The thermally sensitive element may be disposed between a fixed wall of said housing and a support member that is fixed to said pin and may be moveable relative to the housing.
The thermally sensitive element may be a coil of memory metal that expands when reaching said predetermined temperature. However it may alternatively be constructed of shape memory alloy that changes shape upon reaching the predetermined temperature or any fusible element that melts at said predetermined temperature.
The locking member is preferably pivotally disposed in said housing pivots to released state.
According to a second aspect of the present there is provided a fluid damper comprising a retractable barrier for closing a duct and a latch mechanism as defined above. The barrier may take any suitable form but in a preferred embodiment it is a foldable curtain comprised of multiple pivotally connected blades.


REFERENCES:
patent: 4080978 (1978-03-01), McCabe
patent: 4555981 (1985-12-01), McCabe
patent: 5533929 (1996-07-01), Attridge, Jr.
patent: 5779540 (1998-07-01), Nailor
patent: 6039030 (2000-03-01), Robinson et al.

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