HYDRAULIC CIRCUIT FOR DIRECTIONAL CONTROL VALVE FOR FOUR POSITION CLOSED CENTER ACTUATED BY PRESSURE PROPORTIONAL CONTROL VALVE

摘要

PURPOSE:To simplify the structure of a hydraulic circuit by composing the hydraulic circuit of a four position directional control valve which is a closed center at a reserving position, and receives pilot pressure sent from a pressure proportional control valve at both the ends of a spool to change to one position for lifting on one side and to two positions for lowering and floating on the other end. CONSTITUTION:When an operating lever 20a is set at a lowering position, a pilot valve 22 functions to increase the pressure of a pump 23 for sending the pressure corresponding to a operating rate to a case 46. The spool 41 of a directional control valve 6 is moved to the right against a spring 42 by the above pressure to move to a position where the other side of the spool 41 abuts on a spring receiver 48. At this lowering position, the pressure oil fed from a pump 2 flows toward the bottom 4B of a blade cylinder 4 to extend the blade cylinder 4 for lowering a bowl. When the operating lever 20a is set at a floating position, the pilot valve 22 functions to further increase the pressure of the pump 23 for giving the pressure corresponding to the operating rate to the case 46. The spool 41 is moved to the right against the resultant force of the springs 42,47 by the above further increased pressure to make spring receivers 43,44 abut for floating the bowl.