| 摘要 |
A fluid drilling head has a plurality of nozzles ( 3, 4, 5, 6 ) in a rotatable nozzle assembly ( 2 ) to provide high pressure cutting jets ( 7 ). The head is provided with a gauging ring ( 10 ) having an annular clearance ( 11 ) to the rotatable nozzle assembly ( 2 ) to provide for the passage of rock particles eroded by the cutting action of the jets ( 7 ) while regulating the progress of the drilling head in the borehole and controlling drill stalling. A stepped rotatable nozzle assembly having a smaller diameter portion ( 8 ) and a larger diameter portion ( 9 ) to extend the cutting zone of a reaming jet closer to the outer diameter of the gauging ring ( 10 ) is also described and claimed.
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