| 摘要 |
<p>The invention relates to a hydraulic control circuit for a boom cylinder in a work machine, which, when controlling supply and discharge of pressurized oil with respect to a boom cylinder, improves fuel efficiency, work efficiency in combined operations, and improves work efficiency and operationality in work of difficult boom operations such as debris raking-up work and bumping work, etc., wherein the hydraulic control circuit of a boom cylinder 8 is provided with a change valve 22 to hold the first boom control valve 14 at the neutral position N, a communication line E for causing the head side oil chamber 8a and the rod side oil chamber 8b to communicate with each other, an opening and closing valve 21 for opening and closing the corresponding communication line, and a pilot operating check valve 23 that is changed to an unidirectional state where, although an oil flow from the head side oil chamber to the rod side oil chamber is permitted, a reverse flow is hindered, and to a bi-directional state where oil flows in both directions, and further the second boom control valve 15 is provided with discharge means for causing oil discharged from the head side oil chamber 8a to flow into the oil reservoir 13. <IMAGE></p> |
