HYDRAULIC CIRCUIT DEVICE FOR CONSTRUCTION MACHINE

摘要

PROBLEM TO BE SOLVED: To realize smooth acceleration when a turning motor is started and to secure a stable turning operation without being affected by other actuator circuits during composite actions of a turn and a front mechanism. SOLUTION: A turning control valve 9 is arranged on the upstream side of arm and boom control valves 10, 11 on a center bypass line 20. A selector valve 14 capable of being switched to a first position which can connect control valves 9, 10, 11 in parallel with each other or a second position which can connect the turning control valve 9 via a throttle means 24a is provided on a pipe 17. A pressure compensating valve 25 capable of introducing excess oil to the control valves 10, 11 while keeping the front/rear differential pressure constant when the selector valve 14 is set to the second position is provided on the upstream side of the selector valve 14. The second position of the selector valve 24 connects a second relief valve 26 having the set pressure lower than that of a first relief valve 23 to a pipe 27.