| 摘要 |
<p>The invention relates to a hydraulic control circuit of a boom cylinder for 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 first change valve 19 for holding the boom control valve 13 in 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 18 for opening and closing the communication line, and a pilot operating check valve 20 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 a bi-directional state is permitted where oil flows in both directions. <IMAGE></p> |
