(57) The invention provides a door operating mechanism which can be mounted on the pivot
axis of a door. The mechanism comprises a casing 1 in which is guided axially a piston
4, and actuating member 6 therefor. Coupled to the actuating member is a pivot member
7. A compact construction results where the actuating member (6) and pivot member
(7) have complementary helical fingers (29; 33) whereby rotation of the pivot member
(7) gives rise to axial movement of the acuating member (6) and piston (4). The axial
movement in one direction causes hydraulic fluid acting on the piston (4) be pressurised
which provides a return force acting on the piston (4). This can be used to return
a door to a starting position from which it has been displaced. By having fluid acting
on the piston (4) instead of a spring, failure of the fluid system does not give rise
to slamming of the door which is the case where the fluid merely serves as a damping
medium for movement of the door. The construction renders its self-adaptable to automatic
operation.
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