RECYCLING AND COMBINING METHOD FOR HYDRAULIC CYLINDER

PURPOSE:To perform efficient operation by opening a recycling passage if when pressure oil is supplied to a head-side oil chamber negative pressure is lower than a preset value and closing it if over a preset value so that the preset value can be given according to external pressure signals. CONSTITUTION:A spring 13, a stopper 26, a small-dia. spool 12 with a piston 11 inside, and a check valve 10 are housed in a spool 5, to form notch holes 18, 18', 20, 21, 21' therein. Oil pressure from a pilot pump as pilot pressure adjustable through a pilot valve is connected to a pilot oil port 14 of a valve mainframe 4. So, with the slide of the spool 5 to pilot oil chambers 6, 6' according to pressure signals, a bridge circuit 17 and an oil passage 24 to a piston oil chamber 9, and a high-pressure passage 15', a tank passage 16' and an oil chamber 8 to a pilot oil port 14 are open and closed in communication. It is thus possible to perform free instruction of either recycling or not in a load condition through the oil pressure of the pilot oil port 14 and efficient operation.