| 摘要 |
PURPOSE:To attain a high-speed leveling-off operation by a method in which a specific switching position is provided for a direction switch valve for the second arm, the input port is connected to the second pump by a pipeline through a check valve and a throttle valve, and the input ports of direction switch valves for the first and second arms are connected. CONSTITUTION:The input ports 26 and 27 of direction switch valves 4' and 5 for the second and first arms are led to each other by a pipeline 23, and the valve 4' is connected to a direction switch valve 3 for the first boom on the upstream by a bypass pipeline 24 interposed with a check valve 30 and a throttle valve 25. A switching position where the port 26 and the center bypass are closed when the arms are crowded is provided for the valve 4'. When the arms are crowded, the pressure oil of the second pump 1 is introduced into the port 27 through the pipeline 24, the port 26, and the pipeline 23 and then to the bottom chamber 8a of an arm cylinder 8 through the valve 5. The operating amount of operating lever for raising the boom can thus be lessened during the horizontal leveling-off operation. |
