Patent GB-1176932-A (GB)
Title: Improvements in Classifiers for Grading Solid Particles in a Liquid Suspension
Inventor: PHIPPS JOHN DEGORY BARON
IPC: E02F3/94
Filed: 1966-03-11
Abstract: 1,176,932. Grading granular material. FLOATEX SEPARATIONS Ltd. 9 March, 1967 [11 March, 1966], No. 10702/66. Heading B2H. In a classifier 12, Fig. 1, for grading granular material in a liquid suspension, e.g. sand or gravel in water, of the general type described in Specification 779,013 and comprising an inlet chamber 11 for the raw suspension, a preliminary flow-stabilising chamber 13, and grading compartments 20, 30 separating by a weir or as shown, a wall 30a below the free surface L of the liquid, one or, as shown, each grading compartment communicates at its lower end with a hopper 43 (44) which is vertically displaceable in accordance with the weight of graded material therein and is spaced vertically beneath the discharge outlet 21 (31) of the compartment, the hopper outlet being controlled by a valve 60 whose opening and closing are responsive to the vertical displacement of the hopper. The chamber 13 communicates with the compartment 20 through a gap 39 defined between the upper edge of the wall 30a and a lip 16, 16a at one end of a slidable tray 17 which is adjustably secured to the floor 18 of the chamber 13. The rate of discharge of liquid from the compartment outlets 21, 31 is adjusted by means of control valves comprising double-conical valve heads 22, 32 mounted on tubular rods 23, 33. The rod 23 is adjustably supported in a bridge 24 by a nut 25 and the rod 33 may be supported either in the same manner or, as shown, by a float 34 which is used to maintain a constant level of liquid in the classifier. The rods 23, 33 are connected to rings of nozzles 28, 38 which are supplied with clear liquid by means of valve-controlled flexible pipes 27, 37 connected to the rods 23, 33. The grading compartments 20, 30 are enclosed in a tank 40 from which fines-carrying liquid spills over independently adjustable weirs 50-53 into an overflow channel 41 having a discharge pipe 42. A partition 49 across the tank 40 separates the orifice 21 and hopper 43 from the orifices 31 and hopper 44. Each hopper 43, (44) is suspended by deflectable load cells (not shown) from a spigot 45 on the base of the tank 46, each spigot being embraced by a volute chamber 46 supplied with clean liquid under pressure by a pipe 48. The internal wall of each volute chamber is provided with nozzles or with a continuous slot. A flexible seal 47 is provided between each spigot 45 and its respective hopper 43 (44). The control valve 60 at the outlet of each hopper 43 (44) comprises a cylindrical or barrel-shaped body within which is sealed at each end a flexible tubular sleeve capable of compression radially to close a passage through it. The space between the sleeve and the body is connected at 62 to a source of fluid under pressure (not shown) or to exhaust through a change-over valve 61 operated by the vertical displacement of the hopper 43 (44) relative to the associated spigot 45. In operation, when treating for example a water-sand suspension, the width of the gap 39 is adjusted to give the required split between the grades of sand. The raw suspension fed into the chamber 11 passes through an opening 15 into the stabilising chamber 13 where the sand banks up in front of the lip 16. When the sand has built up to its natural surface contour, the tank 40 and the hoppers 43, 44 are full of water. The incoming suspension then flows into the compartments 20, 30, the coarser particles falling through the gap 39 into compartment 20 and the finer particles being carried over into the compartment 30. The control valves 22, 32 adjust the rate of discharge of water, surplus water, carrying a proportion of fines and silt, passing into the overflow channel 41 to be discharged to waste or to cyclones for the recovery of fine sand which may be fed back to the sand discharged from one or both of the valves 60. If too high a proportion of fine particles is being carried down either hopper 43, 44 the nozzles 28 or 38 and the associated volute chamber 45 are supplied with clean water to create turbulence in the discharge outlets 21, 31 and to supplement the natural upward current of water rising to the overflow channel 41. In a modification, Figs. 4 and 5 (not shown) the downstream end wall (30') of the compartment (30) is inclined to meet the end wall of the tank (40). Weirs (54) are fitted on either side of the compartment (30) and a central weir (55) is common to both the compartment (30) and the tank (40). In a further modification, Fig. 6 (not shown) the first compartment (20) is placed outside the tank (40) and the required upward current velocity in the gap (39), which has slightly downwardly divergent, flow-stabilising, depending walls (63, 64) is regulated by the supply of water to the nozzles (28). The compartment (20) has no discharge outlet, as at 21 in Fig. 1, and there is no volute chamber 46 at the entry to the hopper 43. In a still further modification, Fig. 7, the second compartment 30 is connected through a pipe 71 to one or two cyclone separators such as 72 having fines outlet 73 and silt outlet 74. An overflow pipe 71a maintains a constant head of water at the level L. The outlet 75 from the hopper 43 is controlled by a disc valve 77 whose rod 78 is operated by a counter weighted lever 91 which in turn is operated through a link 95 by a counter weighted lever 84 which is actuated through a tube 80 by the vertical movements of the hopper 43.