This invention provides improved body length adjustment means for a vacuum powered lifting system of the type that embodies a variable length lifting body (30) responsive to the differential of pressure inside that body (30) with atmospheric pressure to resolve critical manual control problems. Thus control is provided by proportional movement of a control member (6) 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 (32) by unskilled operators. Thuss, an air injection valve (4) with an air release port is positioned within the lifting body (30) having an elongated slot (26) operable over a control range proportionately change the body length by release of a progressively increasing flow of air into the body (30) to increase air pressure and body length over the critical range of lowering and releasing the work load object (32) in response to a corresponding substantially linear movement of the control member (6). Variable adjustment means (8 and 22) establishes a known upper lift limit by control of the length of the body (30) both under loaded and unloaded conditions, and provisions are made to keep a vacuum responsive work object grasping means continuously operable.