Valve circuit for controlling the motion of a deck edge elevator

Claim 1

An elevator assembly for raising a load from one position to a higher position comprising a platform and a cable and sheave assembly including cables connected to said platform, a hydrostatic engine having a pressure movable member connected to said sheave assembly, said cable and sheave assembly moving said platform to an upper position as said pressure movable member is moved in one direction, said platform being lowered upon movement of said piston in the opposite direction, a pressure source, a main accumulator in communication with said pressure source whereby said accumulator is charged with fluid pressure, a motor feed circuit interconnecting said accumulator and said hydrostatic motor for accommodating distribution of working pressure to one side of said movable member thereby creating a pressure force actuating said movable member in said one direction, said circuit including a control valve for selectively establishing pressure distribution to said hydrostatic engine and for exhausting pressure therefrom, an auxiliary accumulator circuit comprising an auxiliary accumulator, valve control passage means connecting said pressure source and said auxiliary accumulator whereby the latter is charged with working pressure, an intensifier pressure passage extending from said auxiliary accumulator to said working chamber, valve control means in said intensifier pressure passage for interrupting and establishing communication between said auxiliary accumulator and said working chamber, and means including parts carried by movable portions of said elevator assembly for actuating said valve control means upon movement of said sheave assembly to a position proximate to its limiting position corresponding to the uppermost position of said platform, thereby establishing a pressure intensification in said hydrostatic engine following movement of said platform to its uppermost position.