| 摘要 |
PURPOSE:To prevent reduction of a main pump's service life or the generation of noise and vibration by shifting the operation of a main pump into unload condition, when an actuator stands by and by shifting the operation of the main pump into onload condition when the actuator operates. CONSTITUTION:When an actuator 7 stands by, a sequence valve 20 is opened, as a result, the oil pressure in a pipe channel 21 and a pipe channel 4 forms a setting pressure for a relief valve 18. Therefore, a selection valve 19 is shifted into the position A indicated in the figure, permitting the main pump 1 to operate under a mimum discharge rate and almost no pressure. When the actuator 7 operates, the sequence valve 20 is closed and the selection valve 19 is shifted into the position B and the main pump 1 is shifted into onload condition. Therefore, the generation of noise and vibration due to the high pressure operation of the main pump 1 during stand by operation can be prevented. The reduction of service life for the main pump 1 can be also prevented. |
