The present invention relates to the field of interconnections between dampers and ducts, and more particularly, to interconnections which are to be made between ducts, and fire, smoke, or air control dampers which may be part of an overall fire, smoke and/or air handling system.
In order to pass "UL" testing procedures, and in order to provide a maximum degree of safety in a given installation, the interconnections between ducts and a damper are critical parts of a fire and/or smoke protection system. If, for example, proper interconnection is not made between a fire damper mounted in a fire wall and its associated duct extending into the adjacent room, premature separation of that duct from the damper may occur, thereby introducing smoke or fire into a room which may otherwise be free from same. On the other hand, if the interconnection between the duct and the damper is too secure, falling debris which strikes the duct on one side of the fire wall may act through the duct on the damper to pull the damper from the opening in which it is disposed, thereby leading to the spread of fire through the fire wall and the loss of fire protection otherwise imparted by the damper.
Fire, smoke, and air control dampers and their associated duct work are, of course, installed at the job site. It is accordingly important, in order to achieve the desired separation characteristics between duct work, which may be supplied from one source, and dampers which may be supplied from a second source to provide adaptors which are nearly universal and which are not prone to improper installation. Since dampers and duct-work may be installed by a contractor who is not particularly skilled or knowledgeable concerning the desirable separation characteristics of a suitable damper-duct work interface, it is important to provide a simple positive reception of the duct by the adaptor which will counteract any tendency of the installation workman towards over-fastening the duct to the damper.
Heretofore, most damper-duct interfaces have been created using slip joints or brackets which may be riveted to portions of the ducts and dampers, with some attempt being made to establish desirable shearing or release characteristics between the ducts and dampers, as for example, by limiting the number of rivets which may be used between the duct and slip joints. See for example my prior issued U.S. Pat. No. 3,727,663 entitled, "Device For Mounting Fire Damper".