Patent GB-720445-A (GB)
Title: Improvements relating to control apparatus for regulating the movement of a member under an applied force
IPC: F16D57/06
Filed: 1952-10-21
Abstract: 720,445. Fluid pressure brakes. NATIONAL SUPPLY CO., and OIL WELL ENGINEERING CO., Ltd. Oct. 21, 1952 [March 25, 1952], No. 26445/52. Class 103 (1) [Also in Group XXIX] The movement of a work member subjected to an applied force is controlled by a brake released by pressure responsive means connected to a conduit by which fluid under pressure is supplied to a fluid metering device connected to and driven at a speed proportional to that of the work member so that a decrease in the rate of movement of the work member results in a decrease in the speed of the metering device and this increases the back pressure in the conduit and so intensifies the action of the brake releasing means. The invention is shown applied to as feed control device for a rotary drilling rig. The drill string is suspended from a pulley block 18 supported by a tensioned cable 12 passing round a fixed pulley block 17. The cable is wound on a spool 11 having the usual brake rims 13 and its free end is secured to an anchor device 19 as described in U.S.A. Specification 2,488,070. This device compresses the fluid in a capsule 20 to a pressure proportional to the tension in the cable. The spool 11 is driven through mechanism 10 comprising sprockets 14, .15 connected by a chain 16 and a jackshaft 30 connected by a clutch 29 to a further sprocket 26. The sprocket 26 is connected through a further chain and sprocket 25, 27 and a double reduction reversible worm gear 24 to a high-speed shaft 23 to which are operatively connected the fluid metering device 22 and the brake device 21. The metering device is in the form of a gear pump, one of the gears of which is fixed to the shaft 23. The device or pump 22 is supplied with hydraulic fluid under pressure by a conduit 38 from a pump 95 driven by the rotary machine which drives the mechanism 10 or by an independent source of power. The pump 95 draws its supply from a tank 96 to which fluid from the metering device is returned by a line 101. The brake device 21 comprises a friction disc 40 fixed relative to the shaft 23 and engaged on opposite faces by friction shoes 44 pivotally mounted on levers 47, 48 pivoted at their lower ends and urged towards one another at their upper ends by a compression spring 52, Fig. 4, arranged between flanges 55, 56 and adjustable by a screw 58. The levers are pressed apart to release the disc 40 by a hydraulic cylinder assembly 62 comprising a cylinder 63 fixed to the lever 47 and a piston or a diaphragm 66 secured by a movable rod 64 to the lever 48. Hydraulic fluid from the conduit 38 is admitted by a conduit 68 to the expanisible chamber 67 to move the levers 47, 48 apart. The pressure supply to the assembly 62 and to the metering device 22 is controlled by a valve 70, the pressure drop across the closure member 71 of which is maintained constant by a further valve 80. The valve 80 comprises a needle valve 84 actuated by a spring-loaded diaphragm 87 responsive to the pressures on opposite sides of the closure member 71 through connections 90, 91. The valve 84 spills fluid back to the tank 96 through a pipe 100. A spring-loaded relief valve 98 connects the line 91 with a line 99 leading to the tank. The valve 70, the displacement of which is a measure of the flow in the conduit 38, is actuated by a spring-loaded diaphragm 75 responsive to the pressure in a conduit 78. This conduit is connected to a fitting 125 supplied with pneumatic pressure from a line 126 and having an orifice 124 controlled by a flapper valve 121. The valve 121 is pivotally mounted on a spring-pressed lever 117 adjustably supported by a stop screw 120. Pressure variations in the capsule 20 are transmitted through a conduit 113 to a Bourdon tube 115, the free end of which is linked to the flapper valve so that an increase in the tension in the cable 12 results in a further opening of the valve 70 which in turn causes the shaft 23 and hence the spool 11 to speed up. An interlock is provided between the pump 95 and the rotary drive of the mechanism 10 where the pump is independently driven. As shown, this comprises a by-pass valye 105 consisting of a plunger valve 108 maintained closed by the pneumatic pressure which operates the clutch of the aforesaid rotary drive, on a spring-loaded piston 109.