Importance

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Abstract

A hydraulically operated dockboard including a ramp which is hinged at its rear edge to the frame of the dockboard, and a lip is hinged to the forward edge of the ramp and can be pivoted between a downwardly hanging pendant position and an extended position. A main hydraulic cylinder unit interconnects the frame and the ramp and by operating the cylinder unit the ramp can be pivoted upwardly from a horizontal cross traffic position to an upwardly inclined position. A lip cylinder unit interconnects the ramp and the lip, and operation of the lip cylinder unit will pivot the lip from the pendant to an extended position. The hydraulic system is constructed so that fluid is initially supplied to the main cylinder unit by a pump to raise the ramp, and when the main cylinder unit is fully extended, the increased pressure will shift a valve to supply fluid to the lip cylinder unit. The valve is constructed so that the valve will be maintained in the shifted position by substantially less pressure than that required to initially shift the valve. When operation of the pump is discontinued, the ramp will descend and the back pressure generated by the weight of the lip acting against the valve will retain the valve in the shifted position to maintain the lip in the extended condition until the lip engages the bed of a truck.

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First Claim