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Abstract

A spring assembly for counterbalancing a door includes a compression spring and tension members engaging opposite ends of the spring. The tension members can be connected in a conventional horizontally pivoted door mechanism or a track-guided door mechanism, the assembly replacing ordinary tension springs of the pivoted mechanism. The tension members and the spring are maintained in axial alignment during compression of the spring, which can be preloaded as desired. Provision is made for an initial preload corresponding to a lowered position of the door, facilitating installation and adjustment of the spring assembly. The assembly is fail-safe in that the spring is completely enclosed and the spring, if broken, continues to provide support for the door. In the track-guided mechanism, the spring assembly is connected between an anchor and a driveshaft pulley by a cable that is wound onto the pulley. A torque that is produced in the driveshaft by the spring assembly is coupled to a lift pulley on the shaft, the lift pulley being connected to the door by a second cable for applying a counterbalancing force to the door. The power pulley and the lift pulley are of different diameters for matching the load capacity and stroke of the spring to the weight and travel of the door.

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