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1,099,673. Boring earth &c. SIR FRANK WHITTLE. Oct. 13, 1964 [Oct. 15, 1963], No. 40667/63. Addition to 1043692. Heading E1F. [Also in Division F1] Borehole drilling equipment comprises a hydraulic ram 50, a down-hole drilling motor 52, a positive displacement pump 34 driven by the motor to circulate fluid about a flow path, control and loading orifice systems O C , O L (Fig. 2) in series in the path and arranged so that the ram is subjected to the pressure drop over the loading orifice system only, means 9, 10, 20 for varying the area of the loading orifice system to maintain the pressure drops across the systems proportional to one another, means 28 for reducing the area of the control orifice system with increase of flow through it, and means preventing reduction of the control orifice below a minimum. Oil from the pump passes to the orifice Oc by way of an orifice O A , the piston 28 varying the orifice Oc being moved by differential pressure and the head of the piston being too small to completely block the orifice Oc. The piston and needle 9, 10, 20 are moved by oil pressures to vary the orifice O L , the oil by-passing the orifice O L passing along a duct 11, 15 to a chamber 5 above the piston 4 of the ram, and the oil passing through the orifice passing to a reservoir 38 connected to a chamber 6 below the piston 4. The reservoir is maintained at the pressure of the drilling fluid which passes through a duct 31 to rotate the turbine 52 before passing through the bit 54 to remove debris from the borehole. The ram, motor and bit may be slowly rotated bodily from the surface. The turbine is lubricated by oil tram the low pressure side of the pump. In modification the head of the piston 28 is prevented from blocking the orifice Oc by stops or a small flow constantly by passes the orifice Oc. As shown in Fig. 5 the piston 28 has a skirt closing the orifice Oc and the orifice O A is formed in the piston 28. The orifice systems are housed in the piston 4 which is in tandem with a piston 4a. In a further modification (Fig. 6, not shown) the orifice systems are housed in a partition dividing the ram into tandem cylinders. In yet another modification the loading system orifice may be upstream of the control orifice system.
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