Patent GB-1043692-A (GB)
Title: Improvements in fluid pressure motive systems, primarily for borehole drilling
IPC: E21B4/02
Filed: 1961-11-30
Abstract: 1,043,692. Hydraulic apparatus; transmitting power. F. WHITTLE. Nov. 23, 1962 [Nov. 30, 1961 (2)], Nos. 42901/61 and 42902/61. Headings F1P and FIX [Also in Division El] A fluid pressure system e.g. for applying pressure to a bore-hole drill bit comprises a working fluid flow path having two orifices in series, a cylinder containing a working piston subjected to the pressure drop across one of the orifices, and means for varying the area of that orifice so as to maintain the pressure drops across the two orifices proportional to each other. In Fig. 1, the flow-path comprises passages 5, 6 and 7, separated by orifices O c  and O L , and the two sides of working piston 1 are connected by passages 8, 9, with passages 6, 7. The pressure drop across orifice O c  acts on a piston 13 of area A, and that across orifice O L  on a piston 14 of area A 2 . The forces on the pistons are applied to a lever 11 pivoted at 12, with moment arms L 1  and L 2 , and the lever controls a valve member 10 which determines the area of orifice O L . If P 1 , P 2 , and P 3  are the pressures in passage 5, 6 and 7 respectively, the system achieves a balance when P 2 -P 3 = (P 1 -P 2 )A 1  L 1 /A 2  L 2 . The force exerted by piston 1 is thus independent of the speed of the piston, and of its direction of movement. With a positive displacement pump supplying passage 5, the force produced on piston 1 is proportional to the square of the pump driving speed. The orifice O c  may be variable in response to the pressure drop across it, to obtain a force/pump speed law other than a square law. The pistons 13, 14, may be combined in a differential piston, as in the embodiment of Fig. 8, which shows part of a bore-hole drill having at its lower end a ram with an outer member 101 and inner member 102, the latter having at its lower end a turbine driving the bit (not shown) and supplied with mud as working fluid through a passage 111 within member 102. The outer ram member 101 has internal flanges, and the inner ram member external flanges such as 116b thus forming pistons within cylinders, of which one only is shown, having an upper chamber 118b and lower chamber 122b. All the upper chambers are connected in parallel by a passage 123 in the wall of member 102, and all lower chambers are connected in parallel by a passage 146. The turbine drives a gear pump 140, which supplies oil under pressure through passage 123a to a chamber 141 between the large part 142 of a differential piston and a step in its cylinder. The flow path continues through the fixed orifice O c , the adjustable orifice O L , port 147, and passages 146, 146a, to the turbine lubrication system (not shown) and back to the pump reservoir. The pressure between orifices O c  and O L  is connected to chamber 118b through passage 144, and the upper side of the small part 143 of the differential piston is connected to passage 146 and chamber 122b through passage 145. Thus piston 116b is subjected to the pressure drop across orifice O L , and the differential piston moves to alter the area of orifice O L  SO that the pressure drops across orifices O c  and O L  remain proportional. The force exerted by the ram on the bit is thus independent of the feed rate of the ram outer member 101. If the feed rate is much too slow, the ram might reach its full stroke at high speed, causing severe shock. To prevent this, a tappet 150 is arranged to open orifice O L  when the piston 116b bottoms in its cylinder, so by-passing the piston. A one way relief valve 158 may be provided in the piston 116b, to prevent the pressure in chamber 122b exceeding that in chamber 118b by too much, as may happen when the assembly is lifted rapidly off the bottom of the bore-hole. A downward extension 163 of the valve will then make tappet 150 unnecessary. The variable orifice O L  may alternatively be defined by part of the differential piston and a port in its cylinder wall. Means is also provided to compensate for varying pressure in the bore-hole 153, which would vary the nett force exerted by the ram on the bit. Fluid expelled from chamber 122b passes through passage 146, orifice 246, and passage 146a, the orifice area being controlled by a differential piston 245. The upper faces of both parts 242 and 243 are subjected to the pressure downstream of orifice 246, the lower face of the small part is subjected to the pressure in passage 146, and the lower face of the large part is subjected to the pressure in the bore-hole through a filter element 254. Thus if the pressure in the bore-hole increases, tending to contract the ram, piston 245 moves upwardly to enlarge orifice 246, to increase the pressure drop across piston 116b. Variation in the pressure of the turbine mud feed down passage 111 would tend to alter the force exerted by the ram also, so the oil reservoir of pump 140 is kept at the mud feed pressure by a diaphragm 125 subject to that pressure. This pressure thus obtains also in passage 146a and chamber 249. Increase, say, in this pressure, tending to increase the ram force, lowers valve 245 to decrease the area of orifice 246, and decrease the pressure drop across piston 116b.