Constant and variable force tensioning devices utilizing atmospheric

Abstract

Improved constant and variable force tensioning devices are made possible by utilizing atmospheric pressure to provide the restoring force. In one embodiment, a sealed and substantially evacuated canister is provided with a rigid actuating rod which can be partially withdrawn through an opening in one end of the canister against the constant restoring force exerted by atmospheric pressure. In another embodiment, the rigid actuator rod is replaced by a long flexible rod or cable which is capable of collapsing or folding upon itself within the canister, thereby providing the constant force device with a longer stroke. In a further embodiment, the actuator rod terminates in a rolling diaphragm seal which seals off only a portion of the canister interior, eliminating the need for a sliding vacuum seal at the point where the actuator rod protrudes from the canister. In a still further embodiment, the canister is at least partially filled with a low vapor pressure liquid which cavitates when the actuator rod is withdrawn. In this embodiment, the difference between ambient atmospheric pressure and the liquid vapor pressure provides either a constant or variable restoring force, depending upon the amount of liquid in the canister and whether any trapped air is present.