| 摘要 |
PURPOSE:To effectively utilize the oil discharged from an oil-pressure pump by using a system in which the oil discharged from an oil-pressure pump performing the slewing of the three-pump circuits and the acceleration of boom is always flowed into a slewing circuit preferentially, and an excessive slewing oil is directed to a boom accelerating valve only during a combined operation period. CONSTITUTION:In a three-pump system, the pressure oil (b) discharged from an oil- pressure pump P3 is connected to a slewing control valve 32 and boom accelerating control valve 33 in tandem, both control valves 32 and 33 are connected with each other in parallel through a variable sequence valve 34, and bleed-off oil is directed to the boom accelerating control valve 33. The slewing control valve 32 is controlled by a remote control valve 40, a boom control valve 13(d), the boom accelerating control valve 33(d), and the variable sequence valve 34(e) are controlled by the pilot pressure of the remote control valve 50, and the acceleration of a boom cylinder C1 is controlled (g and j). In this case, in the oil-pressure circuit, the pressure are set up to meet the relationships Pcmin <Pa and Pcmin <Pb, where Pcmin is the lowest set pressure value of the variable sequence valve 34, while Pa is the set value of the main relief valves 11, 21, and 31 of the oil-pressure pump, and Pb is the set pressure of the relief valves 62 and 63. |
