| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To allow a jack-up operation, without providing a flow control valve for supplying a pressure oil to a directional control valve for a working element, and a center bypath change-over valve. <P>SOLUTION: This hydraulic drive unit for a hydraulic working machine is equipped with: a first hydraulic pump 21 and a second hydraulic pump 22; and the first boom directional control valve 28 and the second boom directional control valve 29 for controlling a boom cylinder 9, and is further equipped with: a third boom directional control valve 30 for controlling the boom cylinder 9; and a third hydraulic pump 23 supplying the pressure oil to the third directional control valve 30. A jack-up change-over valve 31 has a second change-over position 31b for holding supply of the pressure oils delivered from the first hydraulic pump 21 and the second hydraulic pump 22 to a rod chamber 9b of the boom cylinder 9, in accompaniment to the change-over of the second boom directional control valve 29 and the third directional control valve 30 by an operation of an operation device 32, when pressure of a bottom chamber 9a of the boom cylinder 9 is prescribed pressure or less. <P>COPYRIGHT: (C)2011,JPO&INPIT</p> |
