| 摘要 |
Drill rod holder (10) for clamping a pair of jaws against a drill rod (40), by a piston-cylinder arrangement (22). A first of the jaws is fixed and a second jaw (36) is movable by the piston-cylinder arrangement. A medium under pressure is introduced into the cylinder to urge the piston (26) and the second jaw attached thereto to release the second jaw from the drill rod. The cylinder (2) is pre-filled with a pressurized gas (46) acting on the piston (26) to urge the second jaw (36) against the drill rod to clamp the drill rod (40) between the jaws when the gas pressure exceeds the medium pressure. The second jaw (36) is arranged to move away from the first jaw (34) when the medium pressure exceeds the gas pressure.
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