HYDRAULIC CONTROL CIRCUIT FOR PILE-DRIVING HAMMER

PURPOSE:To prevent the rising of oil temperature and to absorb a surge pressure at a falling time of a hammer, by a method wherein a pipe line with a relief valve, connecting pipe lines for connecting a direction switch valve and a hydraulic cylinder, is installed, and an accumulator and a bypass pipe are mounted at a return pipe line. CONSTITUTION:In a hydraulic circuit in which a hydraulic cylinder 10 for hammer-striking is controlled by means of a fixed capacity pump 2, a control valve 4, variable capacity pumps 3, 3' control valves 4A, 4B, switch valves 8, 8' and a direction switch valve 9, drive pipe lines, which connect together the direction switch valve 9 and the hydraulic cylinder 10, are connected through a relief valve 151, and an accumulator 18 is positioned at a return pipe line 11. Additionally, a bypass line 131 is branched from the return pipe line 11 through a checking valve 141, and this contributes to the prevention of the rise in oil temperature and reduction of an adverse influence exerted by a surge voltage.