707,410. Gravity-separation apparatus. NORTH THAMES GAS BOARD. June 4, 1952 [June 4, 1951], No. 13231/51. Class 46. [Also in Groups XXIX and XXXIV] Apparatus for removing sludge from a settling tank comprises a run-off conduit leading from interior to exterior, a valve associated with a valve seat in the conduit to open or close the conduit, the valve moving in one direction in response to a reduction of pressure in the conduit and in the other direction in response to at least partial restoration of the pressure in the conduit, and means whereby the pressure variations in the conduit are utilized to effect movement of the apparatus relative to the body of sludge in the tank. A pipe 47, Fig. 1, mounted diametrically in a tank 1 is rotatable with respect to a union member 52 to which is also connected a fixed sludge discharge pipe 54 leading to an outlet below the normal level of water in the tank. At the ends of the pipe 47 are identical apparatuses 3, 3<SP>1</SP>. The apparatus 3 comprises pipes 9, 24 of dissimilar cross-section connected at 44 and each commmunicating with one end of a casing 4, Figs. 3 and 4, having valve-seat bushings 5, 6 and pistonguiding bushings 7, 8. Valves 11, 16 are secured on rod 13 at such a distance apart that when one is off its seat, the other is on. Between the valves are arranged pistons 20, 21, spacers 23 and a spacing tube 22 to which is secured an abutment member 65. Baffled inlets 27, 33 communicate with piston-valve-seat spaces 56 and 55 respectively. The casing portion between the pistons is open to the tank interior through an aperture 57. In the position of Fig. 3 sludge is forced through holes 31, 30, 26, past valve seat 10 and along pipes 9, 47 and 54 by the hydrostatic head between the tank water level and the sludge outlet. This flow gives rise to a fall in pressure on the left of piston 20 compared with the pressure on the right of it. Piston 21 is balanced by reason of the facts that sludge has access to both sides and valve 16 is closed. The whole piston-valve assembly accordingly tends to move to the left but is prevented from doing so by the encounter of the abutment member 65 with a forked arm 64 which straddles the spacing tube 22 and is connected to an anchor arm 63 pivoted to a carriage 60 constrained by pins 61 to travel along a rail 58, Fig. 1. The turning moment applied by the abutment 65 causes the anchor arm 63 to rotate about its pin 62 and jam against the rail 58, holding the carriage 60 at rest. The piston assembly thus cannot move, and the resulting reaction causes the casing 4 to move to the right, and thus the pipe 47 to rotate about the union 52, Fig. 1. To prevent the resilience of the sludge from forcing the casing 4 and pipe 47 back again, a sprag mechanism 127 to 131, Fig. 1, provided on the pipe 9, and similar to the mechanism 60 to 63, operates in opposite phase on the rail 58. The movement of casing 4 ends when valve 11 closes, the valve 16 now being off its seat. Flow of sludge through openings 43 to 39 in inlet 33, and through hole 32 and pipe 24 to the sludge outlet reduces pressure to the right of piston 21 while piston 20 is now balanced. The valve-piston assembly now tends to move to the right and is free to do so, moving the carriage 60 with it along the rail 58 by engagement of an arm 67 on the spacing tube 22 with a lug 66 on the carriage. Backward movement, by reaction, of the casing 4 and pipe 47 is prevented by the sprag mechanism 127 to 131. The assembly comprising pipe 47 and apparatuses 3, 3' thus rotates intermittently in the tank 1. In the modification of Fig. 7 only one valve 77, having a piston 74 secured to it, is provided, the other piston 72 being separate from it. Only one discharge conduit, constituted by a downwardly-depending baffled inlet 103 (not shown) below an opening 104 in a casing 71, the opening 104, valve-chamber 75, space 71A and pipe 87 (corresponding to pipe 47) is provided. The pressure and flow conditions are such that hydrostatic pressure causes pistons 74 and 72 to move inwards together, springs 84 and 80 respectively being thereby compressed. Inward movement of piston 72 causes movement of a carriage 92 clockwise along rail 91, movement of the casing 71 being prevented by sprag mechanism 99 to 101. When flow and pressure conditions are such that the pistons are to be restored, backward movement of piston 72 is prevented by locking of the carriage 92 in the manner previously described, whereupon the spring 80 in extending to its normal length forces the casing 71 onwards in a clockwise direction. The spring 84 serves only to restore the piston 74 to the position shown in Fig. 7. In the modification of Fig. 7 shown in Fig. 9 piston 74, valve 77 and spring 84 are dispensed with and that end of the casing 71 is closed by a plate 105. Below the aperture 104 an inlet tube 110 constitutes a cylinder for a piston comprising spaced apertured baffles 116, a valve stem 115 and a valve 114. The force tending to restore valve 114 to open position is in this case provided by gravity. The other piston and mechanisms 92 and 101 are provided as before. The forms of the invention shown in Figs. 1 and 7 may be modified by employing flexible diaphragms instead of pistons. In Fig. 10 the run-off conduit is constituted by a casing 122 and a pipe 126 leading to an outlet below the tank (not shown). When there is no flow in the conduit, hydrostatic tank pressure flexes a diaphragm 123 connected to a valve 125 which thereupon opens. Flow of sludge in casing 122 and pipe 126 equalizes pressure on either side of the diaphragm 123 which accordingly closes the valve. Relative movements of valve mechanism and casing may be used to bring about step-by-step progression of the apparatus as before. According to the Provisional Specification, the run-off conduit may be a vertical tube extending through the tank bottom with a box having a diaphragm (as in Fig. 10) disposed, diaphragm uppermost, so as to envelope both the inlet end of the tube and a valve controlling the inlet end. The diaphragm, valve and valverod assembly are biased to valve-open position, and restricted apertures are provided in the box so that on flow of sludge therethrough to the conduit a pressure drop occurs in the box and the diaphragm is flexed to close the valve. Flow ceases, the valve is biased open and the cycle is repeated. In another embodiment a rotating tube with a central outlet for sludge (as in the Complete Specification) has at each end a metal box in the form of a shallow drum, the outer end wall of each box including a diaphragm and the lower side wall of the box having a restricted inlet aperture. A valve rod extends axially through the tube, is fixed at both ends to the diaphragms and has on it two rubber valve discs spaced apart by a distance slightly in excess of the length of the tube so that when one end of the tube is closed the other end is open. The diaphragm connections are such that they are normally flexed inwards when a cock in the run-off conduit remains closed. When the cock is opened the valve rod is reciprocated rapidly, the valves opening and closing alternately. The reciprocating movement is utilized to rotate the tube. Tubular scoops facing in the direction to dig into the sludge deposit, and leading to the inlet apertures, may be provided on the boxes, the entrances to the scoops being covered with wire mesh. One or more pressure release holes may be provided in the walls of the boxes directed towards the mass of sludge so that a jet of liquid is directed into it each time the valve is shut and the diaphragm flexed inwards of its box.