| 摘要 |
PROBLEM TO BE SOLVED: To improve responsiveness against jamming, eliminate abrupt pressure fluctuation of hydraulic equipment, reduce shocks and vibration, increase durability, simplify circuits, and reduce cost. SOLUTION: In a drilling machine in which a normal rotation pipe line 15 and a reverse rotation pipe line 16 are connected to a drill rotation motor 13 of a rotary mechanism from a rotation control valve 14, and an advancing pipe line 18 and a retreating pipe line 19 are connected to a feed motor 7 of a feeding mechanism from a feeding control valve 17, a main relief valve 21 with a vent is provided in the advancing pipe line 18 of the feed motor 7, and a pilot operation switching valve 41 usually opened is provided in a vent pipe line 23. A pilot pipe line 43 is connected to a pilot port of the pilot operation switching valve 41 through a sequence valve 42 from the normal rotation pipe line 15 of the drill rotation motor 13.
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