| 摘要 |
PURPOSE:To smoothly perform turning operation by providing priority to a turning circuit when turning and arm operation are concurrently performed by a method in which a turning control valve and main control valve for arm, etc., are connected in parallel and a variable sequence valve is provided in the upstream side of the main control valve. CONSTITUTION:A turning switching valve 51 to control a turning motor M3, a right side propelling motor control valve 42, a speed control valve 43 for arm 1, and a speed control valve 44 for boom 2 are connected with an oil-pressure pump P2 in parallel. Then, a variable sequence valve 7 consisting of an outside pilot type balance piston relief valve 41 is provided on the upstream side of said main control valves 42, 43, and 44, whereby working oil is bleeded off. On the other hand, the turning control valve 51 is switched by a turning remote control valve 6 so as to lead the secondary pressure of the remote control valve 6 through a shuttle valve 64 to the set pressure port 70c of the variable sequence valve 7 for controlling the pressure of the turning working oil. |
