GB1061896A - Hydraulic classifying apparatus siphon control - Google Patents

Abstract

1,061,896. Classifying granular materials. DORR-OLIVER Inc. March 6, 1964, No. 9523/64. Heading B2H. In a hydraulic classifier for separating solid particles according to their settling rate in a body of upwardly flowing liquid in a vessel 10 and including a siphon 40 for discharging as a slurry rapidly settling (e.g. coarse) solid particles which accumulate adjacent the bottom of the body of liquid and a conduit 60, 58 for supplying dilution liquid to the inlet end 42 of the siphon for facilitating the siphonic flow, a pressure sensing device 30, 32 is provided for sensing fluid pressure at the bottom of the body of upflowing liquid and a controlled valve 64 is installed in the conduit 60 and is responsive to the pressure sensing device to cut off dilution liquid flow when the sensed pressure falls below a predetermined value. The material to be classified is introduced in a slurry via a pipe 12 and water is supplied via a valved pipe 20 to a chamber 18 at the bottom on the vessel 10 and passes upwardly through a perforated plate 14 carrying with it the fine particles for discharge in a launder 28. The coarse particles settle above the plate 14 and are removed by means of the siphon 40. The lower end of the siphon leg 46 is equipped with a diaphram 54, the closure or opening of which is controlled by a three-way valve 48. Water is also supplied via a conduit 62 controlled by a valve 68 and the conduit 58 to the siphon end 42 to prime the siphon. The valves 48, 64 and 68 may be operated by solenoids 56, 66 and 70. The device for sensing pressure adjacent the plate 14 comprises tube a 30 open to atmosphere and connected to a bellows 32 which operates a switch 34 making or breaking contact with contacts 36. Pressure at the top of the siphon leg 44 is sensed by means of a bellows 72 operating a switch 76 for making or breaking contact with contacts 78. The solenoids 56, 66, 70 and the contacts 36, 78 form part of an electric circuit, Fig. 2 (not shown). In operation, as the coarse particles accumulate above the plate 14, the resulting pressure at the lower end of tube 30 forces water up the tube and into the bellows 32 which expands causing switch 34 to close, thereby energizing the solenoids 56, 66 and causing valve 48 to exhaust to atmosphere air surrounding the diaphragm 54 so that the coarse particles are discharged from the siphon leg 46 and the valve 64 admits dilution water to the siphon end 42. The negative pressure in the siphon keeps the bellows 72 retracted and hence the switch 76 open so that valve 68 is closed and no priming water is supplied to the siphon. If at any time during operation or at starting the siphon is not primed, the higher pressure in the siphon causes the bellows 72 to expand and hence through closure of switch 76 solenoid 70 is energized causing opening of valve 68. When the desired liquid-coarse solids concentration above plate 14, and hence the pressure, decreases, bellows 32 retracts causing de-energization of the electric circuit and consequent closing of valves 64, 68 and operation of valve 48 to admit air around diaphragm 54 to stop discharge of the coarse solids. Instead of being electrically controlled the valves 48, 64, 68 may be pneumatically or hydraulically operated. Instead of a 3-way valve 48, an inverse modulating type valve may be used controlled by an additional pressure sensitive switch responsive to the height of liquid in the tube 30. A number of classifiers may be arranged in series or parallel.