US2967617A - Hydraulic classifier - Google Patents

Description

Jan. 10, 1961 EVANS ETAL 2,967,617

HYDRAULIC CLASSIFIER Filed March 14. 1 58 A/iamey United States Patent HYDRAULIC CLASSIFIER Robert D. Evans, Pierce, and Harvie W. Breathitt, Jr.,

Lakeland, Fla., assignors to The American Agricultural Chemical Company, New York, N.Y., a corporation of Delaware Filed Mar. 14, 1958, Ser. No. 721,403

Claims. (Cl. 209-158) the character disclosed in United States Patent No.

2,708,517, granted May 17, 1955, on application of Robert D. Evans, a further embodiment of such classifiers being disclosed in United States Patent No. 2,784,-

. 841, granted March 12, 1957, on application of Robert D. Evans.

As explained in more detail hereinbelow, the classifiers of the Evans patents, especially as in the basic form of the first-cited patent, involve a pair of vertically spaced column means, viz. a column defining structure providing a lower, hindered-settling column and an upper, freesettling column, the two columns opening toward each other at a central region of the apparatus, with means at the foot of the hindered-settling column for removing the accumulating faster-settling particles in water and means at the closed head of the upper column for withdrawing liquid which carries the slower-settling particles. The upper column and the region around the space between the columns are surrounded by a relatively large, upright cylindrical tank structure, which is filled with liquid and into which the feed pulp to be classified is supplied. The solids of the feed travel downwardly in the tank to the space between the columns, where they have access to the latter and come into the influence of the liquid rising through the columns, i.e. from appropriate means at the foot of the hindered-settling column for introducing such liquid, e.g. hydraulic water, through a suitable constriction plate or the like.

Although the described apparatus and the improvements of the present invention are applicable to hydraulic classification of a wide variety of particulate solids, such as various minerals, sands, and the like, an important example of their use is in the classification of mineral phosphate, e.g. phosphate ore or fractions of phosphate ore, which consist of particles of various sizes both of phosphate material, and impurity, chiefly or entirely siliceous gangue conveniently identified as silica.

Important objects of the invention are to provide improved classifying and sizing apparatus of the character described, as to achieve cleaner or sharper fractionation of the feed into products or portions having different particle sizes, or more accurately into portions having different characteristics of settling rate. A special object is to provide such apparatus which includes improved arrangements for separating slimes, extremely fine particles and other substantially non-settling material from the tank, e.g. at an upper part, while permitting or promoting the progress of the solids to be classified, toward 2,967,617 Patented Jan. 10, 1961 the region between the upper and lower columns. Another, specific object, is to enhance the removal of slimes and other undesired material by diluting action, without substantially impairing the desired travel of feed to the locality of classifying function.

To these and other ends, the improved apparatus comprises a hydraulic classifier or sizer, for example of the type of the cited patents, including a submerged upper column and a lower column extending beneath the tank, with supplemental and coacting features for removal of slimes and the like. Specifically, such structure includes overflow means disposed centrally of the tank at the upper part so as to afford an annular space, e.g. of com siderable width, between such overflow means and'the surrounding tank wall, in contrast to the conventional provision of an overflow means at the periphery of the tank, extending around it. In cooperation with the central overflow means, means are provided for introducing the feed pulp at about the same level and through the tank wall in a more or less tangential relation to the latter. Such introduction of the feed pulp, preferably projected with considerable force, causes a circular, or indeed at least somewhat vortical movement of the liquid in the tank around the central overflow means. By such circular travel, the separation of fines and the like at the overflow is enhanced because .of the centrifugal action of the circularly traveling liquid. The

solid particles to be classified accumulate toward the periphery of the annular path, for the desired fall or advance to the space between the upper and lower columns, while the extreme fine material, slimes and various foreign substances of non-settling character, travel inwardly to the overflow means, for removal. Thus a highly effective classification is achieved in the doublecolumn structure, by reason of the improved separation of fines, otherwise deleterious to the desired classifying action by settling rate.

For coaction with the described structure, the apparatus also preferably includes, as a further feature of invention, means for introducing supplemental liquid, i.e. water, at a locality of the tank substantially below the overflow level. It is found that such addditional water aids considerably in the separation of slimes or fines, presumably by auxiliary dilution of the solids-containing liquid in the tank and by action which in effect washes or rinses the slimes and other undesirable material from sense, the added water dilutes the slimes or other mathe particles descending in the tank. In a particular terial, for more effective removal at the overflow means, so that the pulp reaching the space between the upper and lower columns is in excellent condition for the ensuing sizing or classifying operations of such columns.

tive to segregate the solids of desired particle size for s the classifying operation and thus to prevent their loss, to any apprecable extent, in the relatively considerable volume of overflow.

The improved apparatus is of special advantage where it is desired that there be not only a classifying action but also a rinsing or cleaning action. For instance,-=in certain phosphate-concentrating procedure, hydraulic classification may be desired with respect to a mineral pulp which has been subjected to previous treatment involving concentrating reagents or other chemicals or the 'llke, including supplemental chemical treatment topromote removal of previously applied reagents. In such operation it is further desirable that the hydraulic classi- 'fier perform a rinsing function as well, i.e. to remove or clean'away such reagent or chemical material. stance, it may be important that either or both of the fractions resulting from the classifying action be un- For incontaminated by the previously introduced or occurring "substances, as in cases where such fraction or fractions may be subjected to subsequent treatment, for concentra- "tion or otherwise, where the reagent would be deleterious or where a reagent of different character must be employed. Instances of such undesired materials are various oils, fatty acids, bases and acids as may be used in treatments of phosphate or other minerals or for cleaning such mineral with respect to previously applied substances 'of this sort.

In the improved apparatus of the present invention, the removal of these materials is greatly facilitated, i.e. in carrying them away by the overflow, with the aided rinsing action of the auxiliary water supply,

such reagents or chemicals thus coming within the category :of substantially non-settling material which the improved pulp feed and overflow arrangement functions to separate, atleast in considerable part.

An embodiment of the invention is illustrated in the accompanying drawings, wherein:

'Fig. 1 is an essentially schematic or simplified view, as

if in central vertical section, of one form of hydraulic classifier according to the invention;

'Fig. 2 is a similarly simplified view, taken as if in horizontal section on line 2--2 of Fig. l; and

Fig. 3 is a similar view, as if in horizontal section,-on

line 3--3 of Fig. 1.

The classifier shown in the drawings is basically of the Evans type identified above, in simplified illustration with some details, structural parts and the like omitted for iclarity. The device comprises a main or outer tank "having an upper cylindrical section 11 and a conical portion 12 which tapers to an opening considerably narrower than the wide section 11, to meet the upper end of the lower or hindered-settling column 14 which consists of .an upright cylindrical portion 15 having a somewhat enlarged, cylindrical pocket 16 at its lower end.

Centrally within the wide tank structure 10 there is mounted (by suitable means not shown) an inverted cylindrical tank 18 closed at its top 19 and having a lower, open mouth 20 spaced directly above the top of the lower .tank section 15. The upper section 18, conveniently ends and having a plurality of side openings into which liquid may flow, just below the top 19 of the upper column. The siphon pipe 22 has a control and shut-off valve 24, which may be a pinch-type valve, and conducts the discharged pulp of slower-settling solids to a desired locality for further handling or use, not shown.

To effectuate hindered-settling in the lower column 14 a considerable supply of water is continuously introduced through a pipe 25 opening into a lower part 26 of the pocket 16, for example substantially tangentially thereof. The lower section 26 is separated from the column above it by a constriction plate 27, i.e. a metal plate having suitable perforations, through which the introduced Water 'flows with considerable velocity, to rise in the column 14 and provide hindered-settling conditions. That is to ,say, as will be readily understood, the solids tending to While other means such as a simple outlet pipe and plug valve can be employed for regulated withdrawal of the accumulating coarser 'or slower-settling particles in the pocket 16 above the constriction plate, the structure shown includes a siphon discharge arrangement of the character disclosed in United States Patent No. 2,714,958, granted August 9, 1955, on application of Robert D. Evans. Specifically such arrangement consists of an upright siphon tube or pipe 30 extending to a locality well above the top of the tank section 11 and there opening into a horizontal and downwardly extending pipe 31, constituting the upper turn and other leg of the siphon. Control of the siphon is effected by a float valve 32 adapted to open or close an air vent 33 at the upper turn of the siphon, the float valve being positioned by the water in a static tube 34 which opens near the foot of the hindered-settling column 14. When the pressure or head at the lower part of the column reaches a desired value representative of a pulp density of the desired particles, the float valve 32 closes so that siphon action may initiate, the density of the pulp at the bottom of the column providing an elevation of liquid greater than hydraulic head alone. Thus a rather concentrated aqueous pulp of the desired coarse or faster-settling particles is removed through the siphon discharge 30-31. Self-startng and desired flow of the siphon is facilitated by supplemental water introduced through a pipe 35 opening into a narrow bell 36 which constitutes the lower opening of the siphon intake pipe 30. The-function of the described siphon discharge will be more fully understood'by reference to the cited "Evans Patent No. 2,714,958, including the further feature of adjusting the sizing or fractionating point by elevating or lowering the float valve 32, i.e. to function only upon greater or less'headas transmitted by the static tube 34.

All of the above-described structure is essentially that of the classifier of the 'Evans Patent No. 2,708,517, from which it will be understood that the entire structure is kept filled with liquid, feed pulp being introduced into the top of the upper tank section 11 so that the particles to be classified descend in the tank 10, around the upper column '18 and move into the space 38 between the upper and lower columns, the conical portion 12 of the tank being arranged to surround such space. The particles there tend to settle, but by virtue of the hindered-settling in the column 14, i.e. the conditions of teeter (particularly .in the lower portion of the column), essentially only the drawn through the discharge pipe 22 will consist essentially only or mostly of the slower-settling sizes. Hence the desired fractionation is accomplished with the respective fractions being delivered by the pines 31 and 22. the flow through these pipes being produced by the introduction of water into the classifier and the conditions of head and flow within the described columns of the latter as explained. Further details and characteristics of operation will be apparent from the cited Evans patents relating to classifiers of this character, it being further understood that improved or alternative structures may be employed here as for other embodiments of such apparatus.

In accordance with the present invention, the feed of pulp to be treated is introduced near the top of the tank section 11 through a pipe 40 which extends horizontally into the tank wall in a substantially tangent relation theretoas apparent from the drawings, particularly Fig. 2. Thus the feed pulp, being an aqueous sus' pension of solids consisting chiefly of the particles to be classified by the action of the upper and lower columns 18, 14, isprojected along the inner wall of the tanKso that a circular or rotary flow of liquid is induced around the inside of the tank, e.g. as indicated by the arrows in Fig. 2.

Instead of providing overflow over the top edge of the tank wall 11, the present apparatus includes a central, conveniently cylindrical overflow box 42 advantageously placed above the upper column structure 18, for example with the top wall 19 of the latter constituting at least the central portion of the floor of the overflow means 42. This overflow box, circular in plan, may have a deeper channel portion 43 around the outside of the column 18, as in the nature of a collecting launder from which a pipe 45 extends outwardly and downwardly to discharge the collected liquid. Conveniently the overflow edge 46 of the box 42 is disposed at approximately the level of the tangential opening 48 of the feed pipe 40, a presently preferred arrangement being to have the upper edge of the opening 48 a little higher than the edge 46 of the overflow box, so that with a slight vortical action of the liquid surface between the tank wall 11 and the overflow 42 there is nevertheless effective and substantial overflow action, with minimum submergence of the opening 48. In some cases, such opening can even be slightly above the overflow level.

The improved classifier also includes means for introducing supplemental water at a locality substantially below the overflow level, e.g. as explained above, most conveniently at a locality around the space 38 between the settling columns. Thus the wall 12 of the tank is 7 there provided with an inner, annular box structure 50 having a short, cylindrical, vertical wall 51 with a multiplicity of perforations, facing the space 38. Water is continuously introduced into the box 50 through a plurality of tangential pipes, such as the three pipes 52,

i 53, 54 (Fig. 3) extending from a hexagonal or other appropriate header or pipe ring 56 having an inlet 57.

While the direction of water inlet effected by the tangential pipe or pipes utilized to introduce this additional water to the classifier is preferably the same as the direction of flow provided by the feed pulp inlet 40, such similarity of flow direction is not necessary in all cases. Indeed the essential function of the box 50 is to provide a dispersion of the introduced water, through the perforated plate 51, and to avoid any large, localized jetting action. Thus the tangential entry of water into the box 50 primarily serves to facilitate the dispersion or distribution of the water passing through the perforated plate, rather than to provide any circular or centrifugal flow within the main body of the tank section 12.

It will now be seen that in operation, the feed pulp consisting of the phosphate or other mineral or like material, in appropriate dilution in water, is introduced continuously through the pipe 40, causing a relatively strong circular or centrifugal flow around the tank 11 at and for a considerable distance below the surface of the liquid in the tank. At the same time, there is a continuing overflow at the edge 46 of the overflow box 42. The circular action in the main body of liquid causes all but the very finest particles of the suspended solids to migrate toward or remain near the outer wall 11 of the tank, at least in such fashion that the liquid approaching and reaching the central, circular overflow edge 46 is essentially entirely free of any but extremely fine particles, slimes and the like. Hence the latter material is carried into the overflow means and removed by the pipe 45. This de-sliming or similar action is enhanced by. the additional water supplied to the tank through the perforated ring 51, which dilutes the liquid throughout the upper part of the apparatus and correspondingly increases the volume of overflow. The greater effectiveness of overflow and of slime or fines removal, by virtue of this added water, is made possible by the centrifugal separating action around the overflow means, such action being effective to keep the great bulk of the supplied particles (having the larger particle sizes desired to be classified in the columns 18, 14) from getting into the overflow. Hence with improved removal of fines, the particles descending through the tank 10 to the space 38 are in better condition for the classifying action, so that the latter is performed more efliciently and with a sharper fractionation at the desired point in the range of particle sizes or settling rate properties present. Furthermore the delivered product or coarse fraction through the pipe 31 and similarly the delivered tailings or fine fraction through the pipe 22 are desirably free of slimes or other unwanted material.

It will be appreciated that the described classifier may be built in a wide variety of sizes and proportions adapted for the desired purpose and capacity in any given case, and may in some instances include other known structure, for instance in that for large and varying capacity the upper column means 18 may be of the multiple type such as shown in the Evans Patent No. 2,784,841. Sim ply by way of example, the following dimensions are suitable for a classifier of moderate capacity, constructed essentially as shown in the present drawing and designed to handle a phosphate mineral feed consisting of phosphate and silica particles of a size distributed throughout the range of 20 mesh to about mesh. The upper tank section 11 has a diameter of 15 feet, this cylindrical portion having a height of 4 feet, with the overflow edge 46 about one foot below the top edge of the tank. The cone portion 12 has an altitude of 6 feet, tapering to a column section 15 which is 3 feet in diameter and has a height of 5 feet, down to the pocket 16. The overall height of the latter is about 4 feet, with the upper center of the shallow conical plate 27 rising about 1 /2 feet from the very bottom of the pocket. Conveniently the structure may here include a drain pipe 65, having a normally closed valve 66, i.e. to provide a drain from the pocket 16 at desired times of shut-down. The diameter of the bottom pocket 16 is 5 feet.

The upper column 18 has a diameter of 3 feet four inches and a vertical height of about 6 feet 6 inches, its lower mouth being spaced 2 feet above the top of the lower column section 15. The overflow box 42 conveniently built( as described above) as an integral structure with the upper column 18, has a horizontal diameter of 4 feet 10 inches, so that the width or radial dimension of the annular body of liquid between the overflow means and the tank wall 11 is about 5 feet.

As indicated, the housing 50 is located so that the dilution water is preferably introduced near the intake of the free-settling column 18. That is to say, this supplemental water flow is supplied either just above such intake, or most desirably, directly around the intake region, viz. the region between the columns 18 and 14, as shown.

As an example of unusually effective use of the described apparatus, it is employed for classifying phosphate mineral material which is derived as the concentrate of roughing flotation cells from which the material had been treated with phosphate-selecting reagents, i.e. so-called negative-ion reagents, comprising tall oil, fuel oil and caustic. Since in this particular operation it is desired that a part of the material discharged from the classifier would be subsequently treated to remove silica, by flotation with positive-ion reagents, the feed to the classifier was preliminarily treated with sulfuric acid to de-oil the mineral. Hence as supplied to the apparatus through the feed pipe 40, the pulp contained not only the defined mineral, but also the described chemicals as well as a proportion of fines and slimes. The particles to be classified consisted of phosphate and silica, with the phosphate particles distributed throughout the range mentioned above and with the silica particles predominantly in the finer sizes. t

Utilizing the classifier in the manner stated, with so called hydraulic water supplied through the pipe 25 to effectuate hindered-settling and with supplemental water supplied through the header 56 and the perforated ring pipe 30-31, and a tailing, comprising the finer phosphate and silica particles through the pipe 22. Both products were considerably de-slimed and rendered substantially free of extremely fine material, while the classifier, both because of its nature and with the aid of the supplemental water supply, exhibited a remarkably effect-ive rinsing action. That is to say, the chemicals were in considerable measure rinsed away from the mineral material, especially with respect to the tailing product through the pipe-22. Hence with a single further rinse of water, such product was in'good condition for subsequent treatment with positive-ion reagent material for iconcentr'ation by silica flotation. Procedure just described, for concentrating phosphate material by the statedgseries of steps, is disclosed and claimed in the copending application of Charles M. Goin, Serial Number 723,852, filed March 25, 1958.

It will now be appreciated that the. apparatus affords unusually satisfactory results for classifying mineral material, especially in cases where it is desired to separate p fines, slimes and other non-settling substances, so as to have a sharp fractionation, yielding effectively cleaned products of respectively different particle size or settling rates.

It is to be understood that the invention is not limited to the specific forms herein shown and described, but may be embodied in other ways withoutdeparture from its spirit.

We claim:

1. Hydraulic classifying apparatus comprising upright liquid column-defining structure having liquid-introducing means at the lowest region thereof, for effectuating classification by settling of liquid-carried solids supplied to a predetermined intermediate locality of said structure, to accumulate faster-settling particles at said lowest region of said structure and to carry slower-settling particles to ,a higher region of the structure above said intermediate locality, removal means respectively connected to said regions for separately withdrawing liquid bodies respectively containing said faster-setting and slowersettling particles, tank means adapted to receive liquid to a predetermined level near the top thereof and opening at a lower part to said predetermined locality of the column-defining structure for movement of liquidcarried solids to be classified, downward through said tank means into said column-defining structure, said tank means having a Wall of substantially circular horizontal section around its upper part, means associated with the tank means at its lower part for introducing supplemental liquid into the tank means to dilute the solids-and-liquid mixture therein and thereby to promote separation of substantially non-settling material from solids descending to said predetermined locality, overflow means disposed centrally of the tank means near the top and spaced substantially inward of said circular wall, to receive overflow, at the aforesaid level, of liquid which carries substantially non-settling material, and means for introducing feed pulp of solids to be classified, through said wall and in approximately tangential relation thereto at approximately the level of the overflow means, to provide circulation of liquid in the tank means around the overflow means, for centrifugally impeding the travel, to said overflow means, of solids which are intended to descend to the aforesaid locality for classification.

"2. Hydraulic classifying apparatus comprising upright liquid column-defining structure having liquid-introducing means at the lowest region thereof, for effectuating classification by settling of liquid-carried solids supplied to. a predetermined intermediate locality of said structure, to accumulate faster-settling particles at said lowest region :ofsaid structure: and to'carry slower-settlingtpar- -wticles .to an upper region of the" structure :aboveithe intermediate locality, removal means at said regions :for

'separately withdrauwing'liquid bodies respectively'containing said faster-settling and slower-settling particles,

tankmeans surrounding part of said 'columnrdefining structure and enclosing the said predetermined locality,

to be filledwith liquid for travel, downward into said locality, of solids to be classified, overflow means disposed centrally of the tank means adjacent the top thereof and spaced substantially inward of the wall of the tank means, and means for introducing feed pulp of solids to be classified, into the tank means at approximately the level of the overflow means, in a direction to effect circular flow of liquid in the tank means around the overflow means, said pulp-introducing means and said overflow means being constructed and arranged to promote centrifugal segregation of solids to be classified, toward the wall of the tank means,and to effectuate overflow of liquid which carries'substantially non-settling material, into the central overflow means.

3. Hydraulic classifying apparatus as defined in claim 2, which includes means for introducing supplemental liquid through the wall of the tank means at a' region substantially below the level of the overflow means, for

promoting liquid overflow and removal of substantially faster-settling particles for discharge through said removing means, upwardly closed upper column means having removal means at the top thereof and opening downwardly at a locality spaced above the lower column means, for effectuating free settling ofparticles in solidscarrying liquid moving upwardly in said upper column means, to separate and discharge slower-settling particles in liquid through said last-mentioned removal means, tank means surrounding said upper column means and the space between the upper and lower column means, to be filled with liquid for travel, downward into said space, of solids to be classified, overflow means disposed centrally of the tank means above the upper column means and spaced substantially inward of the Wall of the tank means, and means for introducing feed pulp of solids to be classified, into the tank means at approximately the level of 'the overflow means, in a direction to effect circular flow of liquid in the tank means around the overflow means, said pulp-introducing means and said overflow means being constructed and arranged to promote centrifugal segregation of solids to be classified, toward the wall of the tank means, and to efiectuate overflow of liquid which carries substantially non-settling material, into the central overflow means. I

5. Hydraulic classifying apparatus as defined in claim 4, which includes means for introducing supplemental liquid through the wall of the tank means adjacent the space between the upper and lower column means, for promoting liquid overflow and removal of substantially non-settling material into the aforesaid central overflow means.

6. Hydraulic classifying apparatus comprising upright tank means having a wide upper section of circular transverse shape and a narrow lower column section opening upwardly into the bottom of the upper section, means introducing a flow of liquid at the foot of said lower column, to effectuate hindered settling of particles in liquid in said lower column, for accumulating fastersettling particles at said foot of the lower column, upper column means comprising upwardly ciosed enclosure means spaced within the upper section and opening downwardly at a locality spaced above the open top of the lower column and means for removal of liquid carrying slower-settling particles from the head of said upper column means, to effectuate free settling in said upper column means among particles in liquid moving upwardly to the removal means, means for introducing a feed pulp of liquid carrying solid particles to be classified into the aforesaid upper tank section at the upper periphery thereof, said introducing means comprising means projecting said feed pulp substantially tangentially of the curved wall of said upper section, substantially horizontally along the inner surface thereof, to provide circular fiow of liquid in the upper part of said upper section, overflow means spaced centrally within said upper section at the top thereof at substantially the level of said projecting means and including overflow-collecting and removing structure submerged in the liquid in the tank above said upper column means, and means for removing pulp of said faster-settling particles from the foot of the lower column means said tangential feed projecting means and said central overflow means serving to promote centrifugal segregation of solids to be classified, for downward movement of said solids to the space between the upper and lower column means, while removing substantially non-settling material in said central overflow means.

7. Hydraulic classifying apparatus as defined in claim 6, wherein the enclosure means of the upper column means includes a substantially horizontal top wall therefor and wherein the overflow-collecting and removing structure comprises an upright, shallow, vessel circular in plan and built integrally with said enclosure means and having a floor which comprises said top wall.

8. Hydraulic classifying apparatus comprising upright tank means adapted at the top thereof to receive feed pulp of liquid which carries solid particles to be classified and having a wide upper section of circular transverse shape and a narrow lower column section opening upwardly into the bottom of the upper section, means introducing a flow of liquid at the foot of said lower column, to effectuate hindered settling of particles in liquid in said lower column, for accumulating faster-settling particles at said foot of the lower column, upper column means comprising upwardly closed enclosure means spaced within the upper section and opening downwardly at a locality spaced above the open top of the lower column and means for removal of liquid carrying slowersettling particles from the head of said upper column means, to effectuate free settling in said upper column means among particles in liquid moving upwardly to the removal means, means near the downward opening of said enclosure means of the upper column means, for introducing supplemental liquid into the tank means, to dilute the mixture of liquid and of solids descending to said downward opening, in said tank means around said enclosure means, and thereby to promote separation of substantially non-settling material from solids advancing to the space between the upper and lower columns,

above said upper column means, and means for removing pulp of said faster-settling particles from the foot of the lower column means, said tangential feed projecting means and said central overflow means serving to promote centrifugal segregation of solids to be classified, for downward movement of said solids to the space between the upper and lower column means, while removing substantially non-settling material in said central overflow means.

9. Hydraulic classifying apparatus as defined in claim 8, wherein the upper tank section comprises a conical portion tapering to join the narrow lower column section and surrounding the space between the upper and lower columns in spaced relation therefrom, and wherein the means for introducing supplemental liquid comprises a housing associated with said conical tank portion extending horizontally around said tank portion and having a perforated wall surrounding the said space be tween the columns for dispersing liquid from the housing into the tank around the said space, and means for supplying liquid to said housing.

10. Hydraulic classifying apparatus as defined in claim 9, wherein the last-mentioned liquid-supplying means comprises a plurality of pipes substantially tangentially entering the housing at mutually horizontally spaced localities, for directing the liquid along the housing to promote uniformity of liquid dispersion through the perforated wall.

References Cited in the file of this patent UNITED STATES PATENTS 1,301,544 Crombie Apr. 22, 1919 2,259,029 Fisher Oct. 14, 1941 2,361,207 Horsfield Oct. 24, 1944 2,373,051 Phipps Apr. 3, 1945 2,708,517 Evans May 17, 1955 2,738,068 Marston Mar. 13, 1956 2,784,841 Evans Mar. 12, 1957 2,790,554 Work Apr. 30, 1957 2,829,771 Dahlstrom Apr. 8, 1958 FOREIGN PATENTS 361,513 France May 26, 1906 489,047 Canada Dec. 23, 1952

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