Control arrangement, preferably for remote controlled, hydrostatically operated hoist machineries

A hydraulic hoisting system comprising a cable drum, a hydraulic motor coupled to said drum for driving said drum, a variable displacement hydraulic pump coupled to said motor for driving said motor, and a fluid actuated control system for varying the displacement of said pump, said control system comprising a rod mounted for translational movement toward and away from a predetermined neutral position, means connecting said rod to said pump for controlling the displacement of said pump in dependence upon the position of said rod relative to said neutral position thereby to control the rotational speed of said hydraulic motor and of said cable drum coupled thereto, means for selectively moving said rod comprising a hydraulic cylinder having a piston therein connected to said rod, spring means connected to said rod for resiliently resisting movement of said rod, friction means coupled to said rod for frictionally resisting movement of said rod, and a controllable fluid pressure source connected to said cylinder, said pressure source including means operable to selectively supply substantially zero fluid pressure or a first fluid pressure in excess of said zero pressure or a second fluid pressure in excess of said first fluid pressure from said source to said cylinder, said cylinder being responsive to the continued application of said first fluid pressure to said piston to move said rod from said neutral position to an intermediate position located between said neutral position and a predetermined limit position, and said cylinder being responsive to the continued application of said second fluid pressure to said piston to move said rod from said intermediate position to said limit position, the forces imposed on said rod by said spring means and by said friction means being so related to one another and to the magnitude of said first fluid pressure that, when said rod is moving from said intermediate position toward said limit position in response to the application of said second fluid pressure to said piston, a change in fluid pressure at said piston from said second fluid pressure to said first fluid pressure when said rod is at any selected position between said intermediate and limit positions is operative to halt further movement of said piston and the rod connected thereto and to maintain said rod and piston at said selected position between said intermediate and limit positions.