To hold the blades together and in their open position
It is important that an air/smoke/fire control damper be capable of withstanding intense heat and/or air pressures which may impinge on either side of the damper for substantial periods of time, such as during a fire. Due to the extremeconditions to which such dampers are subjected, it is necessary to provide blade and frame constructions which reliably combine to form a tight, positive seal capable of effectively closing off the air duct, opening or plenum with which the damper isassociated, to maintain a specified fire/smoke rating.
To meet this need, a number of folding blade fire dampers have been developed. Such devices generally utilize a plurality of rotating blades which are capable of forming a seal with any adjacent blades, as well as with the damper frame. However, this seal is often prone to leakage unless relatively precise alignments and tolerances are maintained. This problem is aggravated by the fact that a smoke and fire damper must be able to function effectively in a relatively dirty environment,often years after it has been installed. Moreover, using a multiplicity of separate blades has the disadvantage of imposing a greater resistance to air flow through the damper during normal operating conditions.
In an attempt to overcome these problems, rotating blade fire and smoke dampers of the prior art are often fabricated from extremely heavy materials which are not prone to easy bending or deformation in the presence of heat. Further such damperblades are generally mounted within the damper using distinct hinges or pivots which are separately provided for the purpose of aligning each of the blades for rotational movement, and to ensure proper inter-engagement of each blade with any adjacentblades to form a seal which will not open in the presence of heat or excessive pressure. As a result, such damper constructions are often cumbersome, and relatively complex, both in operation and manufacture. Moreover, such damper constructionsgenerally present a significant resistance to air flow, often producing unacceptable losses.
Sometimes it is desirable to provide such dampers with springs which force the blades of the damper to their closed position. My previously issued U.S. Pat. No. 3,889,156 illustrates the use of a spring in this regard. However, such springshave generally not been used in the absence of a separate locking device which directly restrains the blades during the occurance of a fire, since the heat of the fire can often cause such springs to lose their strength, and thus their effectiveness.
In therefore remains desirable to develop a damper construction which operates effectively in the presence of a fire, overcoming the foregoing disadvantages, but which provides a streamlined open blade profile capable of decreasing air flowenergy losses.
In the description which follows, a fire damper is disclosed for use in air ducts and the like. Generally the damper remains open, in a streamlined configuration, under normal operating conditions. However, in the event of a fire the damper isequipped to automatically snap shut and prevent the spread of fire through the duct work.
In accordance with the present invention, a novel damper latch is disclosed which ensures quick and reliable operation of the damper, in the event of a fire, through the interplay of several unique features. Positive closure is accomplished eventhough the fire damper may sit in a duct for an extended period of time without a fire occurring, despite the resulting accumulation of dirt and grease on the duct hinges and blades, etc.
In a preferred embodiment, two blades are pivotally engaged by a crossbar including two longitudinally extending hinge elements. The crossbar bridges the duct opening and is attached, at each end, either to the damper frame or flange, ordirectly to the duct walls if desired. In the open position, the blades are substantially parallel to one another and to the direction of air flow through the duct so that only the thin blade edges are encountered by the air flow, thus minimizingresistance to air flow through the duct.
To hold the blades together and in their open position, a heat sensitive latch is provided which includes a strap attached to the surface of one of the damper blades at one end and having a slotted portion at its other end; a hook associated withthe slotted portion of the strap and capable of extending over the edges of the damper blades; and a fusible link extending between the hook and attachment means associated with the remaining damper blade. In use, the fusible link is weakened andsevered by the heat of the fire, releasing the hook and permitting the damper blades to assume their closed position. Preferably, spring means are used to bias the blades toward their closed position. Although preferred, such spring biasing is notalways needed. For example, the blades may be allowed to close under the influence of gravity if desired.
Various means can be employed to limit rotation of the blades once they have reached the closed position. For example, an inwardly depending flange can be attached to or made part of the damper frame. Alternatively, releasable spring clips canbe mounted on, or adjacent to, the flange to hold the blades in the closed position. In either event, after the fire is over, the blades can then be reopened and reset to their normal operating position, for subsequent use.
It is desirable to prevent not only the spread of fire, but also to prevent the high temperatures which accompany a fire from being conducted through to the other side of the duct when the damper is closed. Accordingly, each damper/bladecombination is configured to provide a solid, single plane barrier for maximum security against heat transfer by radiation and convection. In addition, as shown in my U.S. Pat. No. 4,146,048, insulation material can be placed over one or both surfacesof the blades without changing the basic configuration of the damper, and in most cases, without interfering with either the air flow through the duct or the action of the blades.
The latch mechanism of the present invention may be used in conjunction with a variety of different damper types including both single and double blade dampers; as well as round, square or rectangularly shaped dampers; with or without springbiased assistance. Accordingly, the simplified construction disclosed herein provides a method for easily fabricating and inexpensively producing dampers having an improved heat sensitive latch for operating the damper blades.
Using such dampers in conjunction with ducts having relatively large cross-sectional areas often requires the damper to have relatively large blades, which generally become less able to withstand the pressures developed within the duct as theirsize increases. Accordingly, additional precautions must be taken to prevent such blades from buckling during a fire. Previously, this had been done using sturdier, heavy gauge materials to form the blades. In accordance with the present invention,reinforcing locking devices are provided which contact the blades upon closure, and which serve to keep the blades closed as long as a heat stimulus remains. After the heat stimulus has passed, these reinforcing locking devices are adapted to eitherrelax by themselves, or by an external force, to release the blades and permit the damper to be reopened.
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