Vertically opening counterweight operated doors - is linked by bearer chains to reserve chains at separate points

摘要

The door opens vertically by means of a counterweight, which is linked to it by at least one bearer-chain. The door is designed to eliminate accidents caused by non-functioning of the holding mechanism in conventional doors of this type. This is achieved by linking each bearer chain (6,7) to a reserve chain (8,9) so that the points of application on the counterweight (14) are different. If one of the bearer chains breaks, the reserve chain continues to link the door to the counterweight and the door functions normally. Because of the difference in application points, the unusual position of the counterweight will be quickly noticed and repairs made. A holding mechanism is unnecessary which makes the door cheaper to manufacture and reduces maintenance costs.