Patent ID: 6860343

Claim:
Drill rod holder ( 10 ) mounted on a support ( 6 ) for clamping a drill rod ( 40 ), in surface and underground drilling equipment, said drill rod holder comprising a first jaw ( 34 ) arranged to co-operate with a second jaw ( 36 ) for applying a clamping force against the drill rod ( 40 ) from opposite sides thereof; a piston-cylinder arrangement ( 22 ) in which a piston rod ( 28 ) is attached at one end to a first side of the piston ( 26 ) and cooperates, at an opposite end, with the second jaw ( 36 ); a medium supply inlet ( 48 ) in the cylinder ( 2 ) through which a medium under pressure is introduced to act on the first side of the piston to pull the piston rod ( 28 ) into the cylinder ( 2 ) and thereby release the clamping force on the jaws ( 34 , 36 ) so that the jaws can be separated, the cylinder ( 2 ) on a second side of said piston ( 26 ) being pre-filled with pressurized gas ( 46 ) acting to exert a pushing force on the piston ( 26 ) and thereby on the second jaw ( 36 ) via the piston rod ( 28 ) such that the second jaw ( 36 ) exerts a clamping force on the drill rod ( 40 ) when the gas pressure exceeds the medium pressure, said second jaw ( 36 ) being arranged to move away from the first jaw ( 34 ) when the medium pressure exceeds the gas pressure, whereby the single piston-cylinder arrangement serves both to open and clampingly close the jaws depending on the pressure of the medium acting on the first side of the piston and the pressure of the pre-filled pressurized gas acting on the second side of the piston.