| 摘要 |
A hydraulic drill string device can be in the form of a percussive hydraulic in-hole drilling machine that has a piston hammer ( 50 ) with an axial through hole ( 51 ) into which a tube ( 35 ) extends. The tube forms a channel for flushing fluid from a spool valve ( 62 ) and the tube wall contains channels ( 40 ) with ports ( 41,42 ) cooperating with the piston hammer for controlling the valve. |
