| 摘要 |
A percussion bit for use with a down-the-hole drilling motor having a hammer which reciprocates in the motor to impact on the upper end of the bit. The bit has a working position in the motor and an idle advanced position. When the bit is in the idle advanced position, the hammer advances to an idle position and, at that time, it is desired for the hammer merely to rest on the bit without impacting the bit. The hammer is reciprocated by fluid pressure and, according to the present invention, a bypass channel is formed directly in the bit which exhausts one of the pressure chambers for the hammer when the bit is in its advanced position. |
