| 摘要 |
This invention provides improved body length adjustment means for a vacuum powered lifting system of the type that embodies a variable length lifting body responsive to the differential of pressure inside that body with atmospheric pressure to resolve critical manual control problems. Thus control is provided by proportional movement of a control member over a substantially linear range producing a smooth progressive movement of the lifting mechanism. This permits non-critical lowering and release of a work load object by unskilled operators. Thus, an air injection valve with an air release port is positioned within the lifting body having an elongated slot operable over a control range proportionately change to the body length by release of a progressively increasing flow of air into the body to increase air pressure and body length over the critical range of lowering and releasing the work load object in response to a corresponding substantially linear movement of the control member. Variable adjustment means establishes a known upper lift limit by control of the length of the body both under loaded and unloaded conditions, and provisions are made to keep a vacuum responsive work object grasping means continuously operable.
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