| 摘要 |
PURPOSE:To drive the uppermost stream actuator at the maximum speed thereof by connecting changeover valves in series to each other, and providing another changeover valve between the lowermost stream portion and a throttle valve for blocking a neutral flow path when the uppermost stream actuator is operated. CONSTITUTION:A changeover valve 3A having a path (g) serving to guide return oil which finished its mission to drive an actuator 4 to a neutral flow path as well as other changeover valves 5, 7 are mutually connected via a series circuit, while a changeover valve 11 to block the neutral flow path when the uppermost stream actuator 4 is operated is interposed between the lowermost stream changeover valve 7 and a throttle valve 9. Hereby, the uppermost stream actuator 4 is given priority in its operation, and thus the actuator 4 can be driven at the maximum speed. Furthermore, pressure is kept on the upstream 10 of the throttle valve 9 when the changeover valves 3A, 5, 7 are located in their neutral positions, whereby a hydraulic pump 1 can be controlled to the side of a minimum discharge amount for saving energy. |
