| 摘要 |
<p>PURPOSE:To improve the working efficiency with a minimum addition of pumps and a simple circuitry by speeding up the work in the case of a small load while a pump circuit is added for unloading when the output of the prime mover is exceeded under high pressure. CONSTITUTION:A prime mover E is driven to feed oil discharged from pumps P1, P2 and P3 to control circuits 14, 15 and 16 via discharge circuts 11, 12 and 13. While the pump P2 fails to be unloaded, pressure generated in the discharge circuit 12 is introduced to a circuit switching valve 38 via a pilot circuit 12b to change it to the position b. Under such a condition, the pressure oil from the pump 1 is all fed to a turning circuit 21 in the turning operation. Thus, the pump P1 is used for turning. In the single operation of associated actuators for the right or left travelling, arms, bucket and booms, the pump P1 serves for speeding up the actuators.</p> |
