| 摘要 |
A drill rig 10 comprises a tower 12 and a drill head 14 that is able to travel linearly up and down the tower 12. The drill head 14 provides torque to a drill string 16 attached to the drill head 14 ad thus to a drill bit 18 coupled to a distal end of the drill string 16. The drill head 14 is traversed along the tower 12 by a plurality of rams 22a, 22b and 22c (hereinafter referred to in general as “rams 22”). The rams 22 provided hold back and pull down for the drill bit 18 via the drill head 14. The rams 22 are selectively operable to enable the hold back and pull down applied to the drill bit to be selectively varied. Thus for example a first of the rams 22a is selected to operate when drilling to a first depth, then the rams 22b and 22c are selected to operate when drilling to a second greater depth; and finally all three rams 22a, 22b and 22c are selected to operate when drilling to a third greater depth. |
