Hydraulic circuit null of change valve for attachment

摘要

PURPOSE:To reduce the cost of a hydraulic circuit by a method in which the center bypass of a switch valve for attachment is always opened, an oil path from an oil path connected to the second hydraulic pump to a switch valve is always closed, and the bypass valve is operated in an interlocking manner with the switch valve. CONSTITUTION:The first hydraulic pump 10 is connected with a switch valve 14 for slewing, a switch valve 16 for arm, a switch valve 18 for running, and a bypass valve 20 to make up the first control valve 22. The second hydraulic pump 12 is connected with a switch valve 24 for boom, a switch valve 26 for bucket, a switch valve 28 for attachment, and a switch valve 30 for running to make up the second control valve 32. The center bypasses 44, 46, and 48 of the valve 28 are always opened and the internal oil path 36 of the valve 28 is always closed by interrupting the supply oil path 34 connected with the pump 12. The pressure oil supply port 50 of the valve 28 is connected to the supply oil path 52 connected with the pump 10 through an outside pipe 54 and is always opened.