HYDRAULIC CIRCUIT FOR DEEP DRILLING MACHINE

摘要

PROBLEM TO BE SOLVED: To provide a hydraulic circuit for a deep drilling machine, having improved operability and safety in the deep drilling machine in which a clamshell bucket is mounted on a telescopic arm via a telescopic cylinder and which performs a series of operations to open/close the bucket and elongate/shrink the telescopic cylinder.SOLUTION: A telescopic cylinder 17 is provided between the telescopic arm and a clamshell bucket 16. A control valve 50 for opening/closing the bucket 16 and ducts 53, 54 are used in combination for elongating/shrinking the telescopic cylinder 17. A sequence valve 58A opens the bucket 16 preceding the elongation of the telescopic cylinder 17. A sequence valve 58B closes the bucket 16 preceding the shrinkage of the telescopic cylinder 17. A bucket relief valve 71 is provided having a lower operating pressure than the sequence valve 58A. A stop valve 70 selectively determines whether the bucket relief valve 71 is loaded into the circuit or not.