1. Field of the Invention
The present invention relates to portable, wheel-mounted hydraulic lifting jacks of the type used to elevate an automobile off its wheels for automobile repair and inspection. More particularly, this invention pertains to a safety mechanism for such a hydraulic jack.
2. Prior Art
Conventional portable lifting jacks of common usage are wheel-equipped and have a low-slung body which allows it to be conveniently maneuvered under the chassis of a car. An example of such a jack is disclosed in U.S. Pat. No. 4,018,421 in which a long tubular handle is connected at its lower end to a yoke which is operatively connected to a hydraulic ram for actuating an elevating linkage. By pumping the handle back and forth fluid may be pumped to the ram to cause the elevating linkage to raise a load. The lower end of the handles of such jacks are commonly rotatably connected to the yoke for rotation about the axis of the handle, there also being a connection with rotatable shaft means controlling a valve for releasing hydraulic pressure to the ram. This arrangement allows a load to be conveniently lowered by a simple twisting of the handle.
A major drawback with such conventional arrangements in portable lifting jacks is that is allows a raised load to be released and lowered so easily that there is the danger that this could occur inadvertently, with harmful results to person and equipment.