BigPatents India

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.