US2714958A

US2714958A - Product discharge means for hydraulic classifying apparatus

Info

Publication number: US2714958A
Application number: US120240A
Authority: US
Inventors: Robert D Evans
Original assignee: American Agricultural Chemical Co
Current assignee: American Agricultural Chemical Co
Priority date: 1949-10-08
Filing date: 1949-10-08
Publication date: 1955-08-09
Anticipated expiration: 1972-08-09

Description

R. D. EVANS Aug. 9, 1955 2,714,958 PRODUCT DISCHARGE MEANS FOR HYDRAULIC CLASSIFYING APPARATUS Filed Oct. 8, 1949 2 Sheets-Sheet l m m w m HTTUIPA/E R. D. EVANS Aug. 9, 1955 2 Sheets-Sheet 2 Filed Oct. 8, 1949 T my Vi J S f w M Y B a Z Z U Q: 5 22 v F A u q a t w w L x u A v 4 1 Z United States Patent PRODUCT DISCHARGE MEANS FOR HYDRAULIC CLASSIFYING APPARATUS Robert D. Evans, Pierce, Fla., assiguor to The American Agricultural Chemical Company, New York, N. Y., a corporation of Delaware Application October 8, 1949, Serial No. 120,240

14 Claims. (Cl. 209-158) This invention relates to apparatus for hydraulic sizing or classification of solids and especially to product-discharge instrumentalities therefor. As contemplated herein, hydraulic sizing apparatus is designed to handle divided solid material supplied as a liquid pulp, e. g. in aqueous suspension, for classification into parts or fractions having different settling characteristics, for instance different characteristics of particle size. In a more particular sense, the invention is related to hydraulic classification equipment involving so-called teeter columns, wherein conditions of hindered settling are realized and put to use. While apparatus of this character can be employed for the hydraulic sizing of a wide variety of ores and other mineral substances, important examples of such material, for which the present invention is peculiarly adapted and designed, are phosphate ores, in the form sometimes referred to as phosphatic sands. For instance, in phosphate mining operations, large quantities of such material are commonly obtained, e. g. as washer tailings or otherwise, and can be treated by flotation, tabling or the like (to yield concentrates rich in phosphate) but must often first be classified, as by apparatus of the above sort, to provide the range or ranges of particle size respectively suitable for the selected type or types of concentration.

In conventional apparatus employing one or more teeter columns, each such column involves means providing an upwardly flowing current of liquid against which the particles of the supplied pulp are introduced. The lower end of the column has a constriction, producing a higher velocity of the rising fluid across the constricted area than in the column above it, with the result that certain particles capable of settling against the rising flow in the upper part of the column can fall no further than the constriction. Thus as distinguished from free-settling conditions, the constricted region can prevent even the fastest settling fraction of the supplied solids from dropping below it, i. e. assuming that conditions are properly selected with regard to the settling rate of such fraction. Accordingly, the particles of mineral material tend to remain in a mass in the tube above the constriction; providing the particles are not too large and the ratio of the area of the constricted portion to the tube cross-section is not too small, such mass of particles will teeter, like the grains in a quicksand. Particles settling are hindered by the solids in teeter, or in other words, by the fact that the liquid and solid mixture, for a considerable distance above the constriction, provides an effective fluid density greater than that of the liquid (e. g. water) itself. The net result is, in effect, a decrease in settling rate of solid particles in the vessel, permitting a more eflicient or sharper classification in accordance with differences of settling rate, than may be ordinarily obtained by freesettling techniques.

A common example of a hydrosizer of such type is a multiple-pocket Fahrenwald apparatus, embodying an array of teeter columns of the character described, arranged for separate removal of the larger particle size product from the foot of each column or pocket and providing passage of non-separated material from one column to the next, in order, at an upper region, while permitting overflow of the fines or tailing at the uppermost level of the machine. That is to say, the pulp of material to be sized is supplied at the head of the first of a series, for instance, of five pockets, the arrangement thus permitting classifying operation on the supplied pulp, somewhat in succession from pocket to pocket.

Heretofore, a common arrangement for withdrawing the desired product, i. e. the faster settling fraction, has involved a downwardly opening passage at the foot of each column, through the constriction plate. Such pas sage is provided with local valve means to regulate the product discharge, for instance a cone valve element movable downwardly into the discharge opening, with suitable electrical control means for operation and adjustment of the valve. While usable, such devices have involved rather complex operating and controlling means, and have nevertheless presented difficulty in the achievement of accurate regulation. It is also found, for instance, that in certain columns oversize particles or pieces tend to clog the valve or at least fail to be discharged, with the result that the operation of the apparatus must be frequently arrested or modified so that the constriction plate and discharge outlet can be cleaned out.

It will be appreciated that the size and density of the particles settling in each teeter column or pocket to the point of discharge depends upon the density maintained within the column, the volume of water introduced upwardly through the constriction plate, and the rate of discharge of the settled particles, these factors being also somewhat interrelated. In consequence, the ineffective or incomplete operation of the available types of devices for controlling product removal, impairs the desired result of a sharp and efficient fractionation, as by undue contamination of the product with undersize particles, or by decreasing the yield of the desired fraction.

Accordingly, a principal object of the invention is to provide hydraulic sizing apparatus of the character described, incorporating new and improved means for withdrawal of the settled product, and overcoming the objectionable characteristics mentioned above. A further object is to provide such apparatus, including means of extremely simple, rugged and highly effective character for withdrawing the settled product, such means being easily and effectively controlled to maintain optimum conditions of hindered settling.

Another object is to afford hydraulic classifying apparatus with improved product removing means, discharging the product at a relatively elevated position, e. g. alongside of the apparatus instead of beneath it, and thus achieving greater convenience in observation and operation (as distinguished from withdrawal at the bottom, where the operator cannot readily see the discharging stream), as well as affording greater flexibility in distribution of the product to localities of use, and serving advantages in plant lay-out, in economy of pumping and other equipment and in general accessibility of the apparatus.

Another chief object of the invention is to afford improved product discharge means, in a hindered-settling column, which effectively removes all of the product, even including oversize and extremely coarse pieces, and thereby avoids clogging and the previous necessity for frequent cleaning-out at the constrictor plate. Another significant object is to provide novel, and extremely simple, automatic control for the rate of discharge of settled particles from a teeter column or the like, in suitable dependence upon conditions in the column, so as toyield a product representing reasonably sharp separation by particle size (or settling rate) and so as to afford uniformity of such separation or such product over long periods of time. Still further objects are to afford improvements in hydraulic sizing apparatus (of both single and plural-column types), and particularly in the efficiency, regulation, convenience, and effectiveness of operations for classifying and removing a desired product.

To these and other ends, certain presently preferred structures embodying the invention are described below and shown in the accompanying drawings, by way of example to illustrate the features and principles of improvement.

Referring to the drawings:

Fig. 1 shows in perspective but highly simplified and thus essentially diagrammatic form, a multiple-pocket hydraulic sizing apparatus embodying the present invention with respect to each pocket, certain structural parts and elements being broken away or removed for clarity of illustration;

Fig. 2 is a similarly simplified, transverse vertical section of a single column or pocket such as embodied in Fig. 1;

Fig. 3 is an enlarged, fragmentary view, chiefly in central, vertical section, showing a hydrostatically-actuated control device included in the arrangement of Figs. 1 and 2; and

Figs. 4 and 5 are fragmentary, diagrammatic views respectively showing certain modified forms of an outlet part of the system illustrated in Fig. 2.

Although the invention may be employed with other types of hydraulic sizing equipment, e. g. other apparatus including at least one column intended to be operated in accordance with the principle of hindered settling (such as the improved apparatus of my copending application Serial No. 107,727, filed July 30, 1949) Fig. 1 illustrates, by way of example, a classifying machine or so-called hydrosizer of the Fahrenwald type described above.

As indicated, the apparatus includes a tank structure having an open top with an overflow edge 12 and a plurality of vertical, transverse partitions 13 dividing the tank into an array of vertical pockets or columns, each designated 14. At one end of the tank 10 there is provided a receiving box or tray 16, into which the pulp feed may be delivered (for example from a supply conduit indicated at 18) and from which such pulp flows into the main body of the tank, over the columns. It will be noted that the upper edges of the partitions 13 are spaced considerably below the overflow 12 at the sides and remote end of the tank, so that the material which does not settle in the first of the pockets may in effect flow on to the next or succeeding pockets, while the actual overflow is confined, as much as possible, to only the very finest fraction. For collection of such overflow, a launder 20 surrounds the top of the tank, e. g. on the three sides other than that occupied by the feed box 16.

Each of the pockets 14 includes a constriction plate or false bottom 22 spaced a short distance above the true bottom 23, to afford a water chamber 22:: into which water is continuously introduced, as from a supply pipe 24, it being understood that a separate pipe is thus provided for each of the pockets 14. The constriction plate 22 has a multiplicity of small, equally spaced holes through which the water rises at a velocity considerably higher than the upward rate of travel which it assumes in the main body of the pocket or column above the plate. As will now be readily understood, the total area of the holes in the constriction plate is such as to afford the desired localized increase of rate of flow, while the holes themselves may be conveniently small enough to inhibit accidental or other unintended passage of particles down through them.

As will also now be appreciated, each such pocket 14 is intended to be operated as a teeter column, affording hindered settling in the dense suspension of particles which accumulates substantially throughout the vertical extent of the pocket, so that a desired, course (or faster settling) product may be removed at the vicinity of the constriction plate 22, while particles which fail to settle tend to accumulate at the top of, or above the pocket and thus pass on to the next in the series. Customarily the pockets 14 are identified by their place in the series, the one nearest the feed box 16 being the first, while the most remote in the illustrated device, i. e. adjacent the end wall 26, is the fifth.

Suitable means, herein indicated by the discharge conduit 27, may be provided for continuous removal of the overflow pulp from the launder 20. Each of the pockets may also have a drain pipe 28 opening through and extending downwardly from the constriction plate 22, with a normally closed valve 30 in each. The pipes 28, however, are not used in the present apparatus for product removal in regular operation, but simply afford means for complete drainage of each pocket at times when such may be desirable. Except as last mentioned, the apparatus so far described may be of essentially conventional character, having such proportions and dimensions as are known to be suitable.

While Fig. 1 also shows principal features of the improved discharge system provided for each pocket (but with certain parts omitted, in the case of some, for clarity), reference is now made to the more detailed view of Fig. 2, which represents a single pocket of Fig. 1, or indeed any teeter column device involving the same general principles of operation.

Structural parts identified in connection with Fig. 1 are similarly numbered and arranged in Fig. 2, it being thus understood that with the drain valve 3% closed and a suitable control valve 32 in the Water supply line 24 open, water is continuously introduced into the Water chamber 22a so as to flow upwardly through the constriction plate 22 and afford an upwardly moving column of liquid in the vertical pocket or vessel 14 above the plate. Continuous overflow occurs at the upper edge 12 and into the launder 26. By virtue of the increased velocity of the water in the vicinity of the constriction plate 22, a condition of teeter is established in the pulp column in the tank 14, affording hindered settling, through the column, of particles which have a desired range of relatively large particle size and which thus represent the fastest settling fraction of the pulp received in the upper portion 34 of the column, the operation being continuous, with respect to water supply, feed of pulp at the top, overflow at the edge 12, and finally, as will now be explained, with respect to the withdrawal of the settled product.

To separate the latter, the apparatus includes a. piping system generally designated 35, and arranged to con stitute a siphon which opens at 36 above but near the constriction plate 22, and extends upwardly to a locality above the tank 14 and hence downwardly to an outlet device 37 externally disposed at a convenient place beside the apparatus. The siphon system comprises a lower pipe section 49 of relatively large diameter and providing at its lower end the downward opening 36. From the upper end of the vertical pipe section 40, a pipe 42 of smaller diameter extends further upward through the tank M to a head or T fitting 43 located at a suitable point above the apparatus. A further pipe assembly 45, of similar size to the pipe 42 or preferably little smaller, communicates with the fitting 4-3 and thus with the pipe 42, and extends outwardly and downwardly from the latter, e. as shown, to a locality outside the column 14 and well below its liquid level 12. The assembly 45 includes a final pipe section 46 which opens downwardly, in the outlet device 37.

The device 37 comprises a cup-like vessel into which an overflow-type discharge pipe 48 extends upwardly so as to maintain a predetermined level 49 of liquid in the cup. The lower open end of the pipe 46, constituting the Outlet of the siphon system 35, is disposed at the same level as the top of the discharge pipe 48. The described assembly operates to eflectuate continuous withdrawal, by siphon action, of a pulp containing the desired, settled fraction from the foot of the teeter column in the vessel 14.

While in some casesthe arrangement may be effective in the simplest form for the intended purpose, it is at present preferred to introduce water in moderate quantity continuously into the siphon structure, with special advantage for sureness of operation and notably for selfstarting as explained below. Thus a supply pipe 50 extends downwardly into the vessel 14, e. g. alongside of the pipe 42, and opens into the head of the pipe section 40, for continuous introduction of water from a suitable source, not shown. It Will be noted that the upper pipe section 42 of the siphon system conveniently projects somewhat, e. g. a few inches, into the otherwise closed, head end of the larger pipe section 40, as shown at 51. The delivery end of the water supply pipe 50 is therefore above the opening of the pipe-42, an arrangement found to aiford smooth and trouble-free operation, both in starting the siphon and in keeping it ready to start.

Assuming that the upper end of the fitting 43- is closed except for its communication with the pipe 45, and assuming that the vessel 14 is functioning as a hinderedsettling column and that the siphon system 35 is filled with liquid, siphon action proceeds continuously, for travel of product pulp through the

pipes

40, 42, 45 and 46 to the outlet cup 37 and thence through the discharge pipe 48 to be conveyed (as by appropriate conduit or like means, not shown) to the locality of use. The graduated size relation of the

pipes

40, 42 and 45 promotes the siphon action, as well as its initiation in the manner set forth below. The larger pipe at the foot of the entering leg facilitates collection and withdrawal of a continuously large volume of the pulp at the bottom of the teeter column, i. e. the pulp comprising the solid particles there accumulating and constituting the desired product. At the same time, and indeed with the aid of the water supplied through the pipe 50, a high velocity is achieved in the remainder 42, of the siphon, for effective removal of the large. quantity of product accommodated by the intake section 40. All of the solids, even oversize particles or pieces, are rapidly swept along through the siphon system, in, a suspension of desirably high density. Indeed, despite the dilution by the supplemental water, the pulp discharged through the outlet box 37 may contain as high as. 55% to 60% solids, representing a liquid of unusual thickness or density for removal by siphon action.

As indicated above, the density maintained in the teeter column and the rate of product discharge are among the interrelated factors governing the size and density of the particles settling to the discharge level, viz. the level of the siphon intake in the present apparatus. While: any of a variety of instrumentalities and controlling devices therefor, including other means controlled by the. pulp density or pressure at the foot of the teeter column, may be employed for regulating the discharge through the siphon 35, the drawings. show a particularly simple and eifective arrangement, which may be entirely automatic and which atfords full uniformity of the product. Such control may be effected, for example, with respect to a small air vent 52 located near the top of the siphon system preferably at its highest point; as. shown, the vent may constitute a. small nipple or tube fitted in the upper end of the T 43. When such vent is closed, a full. gravity flow can be maintained through the siphon from its foot in the column 14,. while opening the vent to the atmosphere will interrupt such flOW.

The pulp pressure at the foot of the column 14, and

thus the density of solids maintained in condition of teeter in the column, may be measured by a vertical,

hydrostatic pipe 54 which opens at its lower end near the constriction plate 22 and the lower end 36 of the siphon. The upper end 55 of the pipe 5 4 is open to the atmosphere, at a sufiiciently high point above the level of liquid in the tank 14, so that throughout a wide variation of normal operating conditions, there will be no flow of liquid out the top of the pipe. in consequence water, essentially free of suspended solids, rises in the pipe 54 to a level determined by the pressure at its foot, i. e. to a level which exceeds the surface 12 of the teeter column by a distance equal to the diflerence, in inches of water, between the actual liquid pressure at the foot of the pipe and the normal head of a pure water column having the height of the vessel 14. For convenience of observation the upper section 57 of the pipe 54 may be made of transparent material, such as transparent plastic.

Since the pulp density within the teeter column is related to the classifying action, for example in that the greater the density the less the likelihood of finer particles reaching the foot of the column, the siphon discharge rate may be effectively controlled in accordance with such density, and thus in a practical way by the pulp pressure at the foot of the column. That is to say, with the water supply through the pipe 24 regulated at a. proper value, the pressure at the discharge level 36 (which is governed by the pulp density in the column) determines the size and specific gravity of ore particles to be discharged. In consequence, the present apparatus includes means for regulating, in elfect, the size of the air vent 52 at the top of the siphon when slight variations occur in the hydrostatic pressure measured by the pipe 54, so that the siphon discharge flow is correlated with the discharge level pressure to maintain uniform, desired characteristics of the separated fraction of solids.

Although other mechanisms may be employed for such regulation, a particularly convenient device (see Figs. 2 and 3) includes a float valve structure generally designated 60 and connected with the vent 52 and the pipe 54. The structure 61) includes a closed, cylindrical chamber 61 having a cylindrical side wall 62 of transparent plastic or the like. A pipe 63 projects down from the base of the chamber and communicates, via the flexible tubing 64, with a T fitting 65 in the hydrostatic pipe 54. In its top wall 66, the chamber 6.1 has an up wardly extending pipe or tube 69 which similarly communicates, via the flexible tubing '70, with the air vent nipple 52. A vent nipple or tube 72 also opens through the top 68 of the chamber 61, affording continuous communication with the atmosphere.

As will now be seen, the chamber 61 is adapted to receive water from the hydrostatic pipe 54-. For response to the level of the water, the chamber loosely encloses a float 74, e. g., a hollow metallic vessel of shallow, cylindrical shape, which has a lower guide stem 75 extending loosely down into the tube 63, and an upwardly projecting, conical valve element 77 which is adapted to be carried into the upper tube 69, cooperating with the latter to constitute a valve between the conduit 76 and the interior of the chamber. Thus when the valve 77, 69 is fully closed, as by the insertion of the valve element 77 to the dotted line position 77a, the vent 52 is effectively closed from the atmosphere. At the other and lower positions of the valve element 77, corresponding opening is effected between the vent 52 and the outside air, i. e. through the upper part of the chamber 61 and the tube 72.

A vertical supporting rod 86 mounted at one side of the sizing apparatus carries a sleeve 81 which, by an attached bracket 82, serves to mount the chamber 61. A clamping screw 84 is associated with the sleeve 81 so that t the latter may be clamped in any desired position of vertical adjustment on the rod 80. Thus the valve device 60 may be set in vertical position to correspond with the hydrostatic head 85 which the pipe 54 should exhtibit (above the overflow edge 12) for desired operation;

- more specifically, the device should be set so that at the desired pulp pressure the water level 86 in the valve chamber (being the same as the level 85 in the pipe 54) will be at a sufficient height to carry the float 74 and its valve stem 77 to the fully closed position 77a of the latter. Upon departure of the pressure in the pipe 54 below a value representing optimum fluid density in the column, the water level in the valve device 60 falls, opening the valve 77 and correspondingly (by the resulting communication of air to the vent 52) reducing or interrupting the flow of pulp through the siphon 35. When the fluid density in the teeter column thereafter builds up to the desired value, the valve again closes and discharge flow resumes.

As indicated above, the graduated diameter of the siphon conduit system, the location of the upper siphon bend 43 at a point not too high above the level 12, and especially the continuous introduction of water through the pipe 50 make the siphon essentially self-priming, in further cooperation with the outlet device 37. In lieu of the latter Fig. 4 illustrates a simpler though less fully effective arrangement, wherein the pipe 45 extends through a reducing fitting 90 to an outlet section 91 of relatively small internal diameter. The narrow pipe 91 tends to prevent or impede backward flow of air up the column 45, such as might otherwise prevent the complete filling of the siphon which is necessary for prompt starting. In the further alternative of Fig. 5 the conduit 45 extends through a return bend or trap-like portion 93 for eventual discharge of the pulp into a collecting box or conduit 94. Since the bend 93 is always filled with liquid, an effective liquid seal is provided, yet without restricting the discharge as in the case of the narrow pipe 91. The outlet box arrangement 37 of Fig. 2, however, is at present preferred, for its further insurance of certainty in starting and for its contribution to smoothness of operation at all times. Ample liquid is always present at the discharge end of the siphon section 46, regardless of surges or the like. Furthermore to the extent that any extraordinarily large or heavy particles or pieces accumulate in the bottom of the cup, they do not clog the discharge flow, and yet they can be easily removed.

The operation of the apparatus will now be largely self-evident from the preceding description. Assuming that the column 14 is filled with water and that water is constantly entering through the pipe 24 at a desired value, and assuming further that pulp to be classified is supplied to the head of the column (as from the feed box 16 in a machine such as shown in Fig. 1), the conditions in the column gradually build up to the desired state of teeter, with the corresponding high fluid density. The resulting pressure at the foot of the column forces water up into the hydrostatic pipe section 57 and also into the branch 64. When the precise optimum level is reached, the float 74 (Fig. 3) rises to close the valve 7769, thus closing the air vent 52. In the meantime,. water flow has been started through the pipe 50 to afford self-priming characteristics in cooperation with the other features named above; indeed as the pulp density builds up in the sizer, even though below the point for siphon operation, water from the pipe 50 flows continuously or in surges to and through the discharge box 37.

In consequence, a full siphon flow commences at once, upon the closing of the vent 52. A continuous and voluminous flow of pulp from the discharge level 36, consisting of the desired product, thereafter takes place so long as warranted by the classifying action of the teeter column. The required coarse or fast-settling fraction is thus discharged continuously through the outlet device 37 and the pipe 48, for use as desired. Finer fractions continue on to the next pocket, i. e. in a multipocket machine, or overflow into the launder 20, depending on the further classifying or sizing function of the complete apparatus.

Simply by way of example, one effective structure embodied, as in Fig. 1, in each pocket of the conventional, five-pocket sizing apparatus herein described had the following dimensions. The height of the overflow edge 12 was 4 feet 9 inches and of the top of the partitions 13 was 3 feet 1 inch, from the constriction plates 22. Each receiving conduit 40 was a section of 4 inch pipe, 21 inches long, with its lower end about 4 inches or so above the constriction plate. The further conduit 42 was a 2 /2 inch pipe having its lower end extending about 3 inches concentrically within the upper closed end of the pipe 40, the upper end of the pipe 42 terminating, at the T 43, about 18 inches above the water lever 12. The sloping portion of the tube 45 consisted of 1 /2 inch pipe and the vertical section, above the part 46, was rubber hose of like diameter, continuing with a length 46 of 1 /2 inch pipe, i. e. about 14 inches long. The discharge cup 37 was 12 inches deep and had an inside diameter of 6 inches, with the mouth of the outlet pipe 48 about 5 inches above the bottom. While these values illustrate a representative, dimensional relationship of the several parts, it will be understood that other sizes and proportions may be used for other circumstances of use, providing the described functional relationships are maintained.

The following is an example of successful sizing operations with the apparatus described above. The feed was introduced into the box 16 at the rate of 750 pounds (dry weight) of solids per minute and consisted of phosphate ore pulp having a solids content of about 70%, and a particle size range from something above 14 mesh to a rather minor content of particles smaller than 65 mesh. To effectuate conditions of teeter, water was introduced through each of the pipes 24 at the rate of the order of gallons per minute, differing from pocket to pocket as necessary, while the supplemental water supply in each pipe 50 was about 10 to 12 gallons per minute. The valve 60 for each discharge system was adjusted to maintain an optimum relation of yield and of sharpness of classification with respect to the product through the corresponding siphon. It was found that after an initially correct setting of the valves on the rods 80, no further adjustment was ordinarily necessary unless there was a considerable change in the nature of the feed. For instance, the apparatus was often run for periods of 48 hours or so without requiring any of the devices 60 to be moved.

Representative analyses of results attained in such operation are set forth in the table below, giving the particle size characteristics of the several siphon discharge products and the overflow or tailings in the launder 20, all percentages being based on dry weight of the recovered solids. The grade of each product is also given as percent B. P. L. (bone phosphate of lime).

Table of product analyses In practice, the products from the first and second pockets were sent to a tabling plant, and from the third, fourth and fifth to froth flotation apparatus, for concentration of the phosphate.

It will be noted that a satisfactorily sharp classification or split was obtained by the operations reported in the table, in that each product represented only a relatively narrow range of particle sizes. In such respects and also in the yields (not reported above) these results were superior to normal results obtained in. the same type of Fahrenwald sizer using the best of previously available discharge arrangements. By way of summary, the results of the present invention in the table above showed that from the first pocket 94.3% of the product was +28 mesh, from the second pocket 99.6% was +35 mesh, from the third pocket 96% was +48 mesh and from the fourth and fifth pockets 99% and 96.9% respectively, were +65 mesh material. In a comparable operation of the prior apparatus as just described, and using similar feed, corresponding figures for the proportions of the products similarly coarser than the stated mesh sizes, from the respective pockets, were 82.8%, 76.3%, 69.3%, 93.2% and 85.2% (in the same order). Furthermore, the overflow in the present apparatus contained somewhat less material of valuable sizes.

These and other comparative operations have shown that the apparatus of the invention alfords a distinctly sharper particle size cut, in that the product from each pocket is less contaminated with unwanted solids of finer size. Furthermore, the actual yield in the first pocket with the present apparatus is much greater than hitherto ordinarily attained in machines of this type, experience with the latter being that in order to avoid both clogging of the outlet and contamination of the product. of the first pocket with fines, the quantity of such product must be reduced to a relatively small value. With the present apparatus, however, the first pocket can perform its full share of the sizing work.

In practical operation, self-priming of the siphon system was found to be. promoted not only by factors noted above (including an adequate, unfailing water supply through the pipe 50 and means such as the cup 37 to. prevent air from backing up into the system during priming) but also by making sure that the siphon pipes and connections were air-tight except for the vent 52, and by keeping the horizontal portion of the siphon as short as possible, e. g. not longer than 2 or 3 feet. In most cases, too, the elevation of the peak of the system above the water level (at 12) in the tank 14 requires careful selection, if necessary by simple tests with the given type of sizing apparatus. If the upper bend, i. e. the top of the pipe 42, is too low, the system may discharge a certain amount of fine solids at times when the cell pressure is below the operating point and the vent 52 is open; if too high, the desired siphon discharge is apt to be slow in starting, especially when the control 60 is set to initiate operation at a ratherlow pressure. Present experience is that an optimum peak location lies about midway between the water level of the tank 14 and the minimum desired level of water in the pipe 54, one specific example of such peak elevation being as stated hereinabove,. and another being a distance of 36 inches or so (above the tank level) for a large embodiment of the so-called double column sizing cell of my above-cited copending application.

In all respects the described structures accomplish the several objects recited above, including an eflfective and reliable automatic control, a simplicity and ruggedness of construction, and ease and convenience of operation. The discharge is readily visible and accessible for sampling, i. e. as distinguished from prior, bottom-type discharge arrangements where'the outletflow cannot be seen and where the operator is compelled to reach under the machine in order to obtain asample. Finally, difiiculties of clogging by large particles, and the necessity of frequent cleaning out are essentially obviated. Even lumps or pieces having a diameter as great as one inch can be carried off through the siphon discharge without obstructing the operation.

It is to be understood that the invention is not limited to the specific apparatus herein shown and described, but may be embodied inother forms without departure from its spirit.

I claim:

1. Hydraulic sizing apparatus comprising, in combi- I6 nation, means providing a teeter column for receiving divided solids to be classified according to settling rate, said means including means introducing liquid to provide upward flow in the column from the foot thereof and said teeter column means being adapted to accumulate solids of predetermined faster settling characteristics near the foot thereof, said teeter column means comprising a tank for the teeter column, having means providing an upper level for liquid in the tank, siphon means opening into said teeter column means near the foot thereof for withdrawing a pulp of accumulated solids, said siphon means extending through an upper region above the aforesaid upper level and thence to a lower region which is below said upper level and outside the tank, said siphon means comprising a conduit opening for discharge at said lower region, and said siphon means including air vent means therein controllable to modify the flow of Withdrawn pulp therein, a hydrostatic column opening in said teeter column means near the foot thereof and extending to an upper locality above said upper region, for rise of liquid in said column to a level measured by the pulp density in the teeter column, and means associated with the hydrostatic column and controlled by the liquid level therein and comprising a valve for controlling said siphon flow-modifying means, to" prevent withdrawal of solids, in said siphon means, that depart from said predetermined settling characteristics.

2. The apparatus described in claim 1, wherein the siphon means comprises conduit structure having successive, vertically extending sections of decreasing diameter, extending vertically away from the aforesaid opening of the siphon means, and wherein the siphon means includes associated conduit means opening into the siphon means at a lower one of said successive sections, for continuous introduction of fresh liquid into said lower section of the siphon means to promote initiation of continuous flow of pulp of accumulated solids in said siphon means when said valve is closed and when the hydrostatic head of pulp near the foot of the teeter column is sufiicient to raise liquid to said upper region.

3. Hydraulic sizing apparatus comprising, in combination, means providing a teeter column, adapted to receive a pulp of solids to be sized, and adapted to provide accumulation of a fraction of high settling rate at the foot of said. column said teeter column means including means introducing liquid to provide upward flow in the column from the foot thereof, siphon means opening into said teeter column means near the foot thereof, for removing pulp containing said accumulated fraction, means for introducing supplemental liquid continuously into said siphon means at a locality spaced from its opening into the teeter column means, to facilitate initiation of siphon action, said teeter column means comprising means pro.- viding an upper liquid level for said teeter column and means for providing in said accumulated fraction of solids a substantially higher pressure adjacent the opening of said siphon means than the static head of liquid alone below said upper level, said siphon means comprising conduit structure extending from said opening near the foot of the column to an upper locality substantially above said upper level and thence to a region outside the teeter column means and below said upper level, said upper locality of the siphon means being disposed below a level corresponding to the hydrostatic equivalent of said substantially higher pressure at the opening of the siphon means, an. air vent in said conduit structure at said upper locality, and valve means for closing and opening said air vent to initiate and interrupt continuous flow of pulp through the siphon means.

4. The apparatus described in claim 3, wherein the siphon means comprises a pipe length of relatively large diameter extending vertically in said teeter column means and opening at its lower end near the foot of said teeter column means to provide the aforesaid siphon opening, and a further pipe of relatively smaller diameter communicating with the upper end of the first pipe length and extending vertically above the latter, said supplemental liquid supply means communicating with said siphon means at the vicinity of the communication of said pipes.

5. The apparatus described in claim 4, wherein the first-mentioned pipe length is closed at its upper end and the second-mentioned pipe projects downwardly within the first pipe to open therein at a locality spaced from said closed upper end, said second pipe being internally spaced from the inner surface of the first pipe and said supplemental liquid supply means opening into the first pipe length at a locality above the aforesaid opening therein of the second pipe.

6. Hydraulic sizing apparatus comprising, in combination, teeter column means including a tank adapted to receive liquid-carried solids for classification and having an overflow level, and means for effecting liquid flow upwardly in said tank to provide hindered settling of the solids in a predetermined lower region of the tank, for producing higher pressure in said region than the static head of liquid alone below said upper level, said pressure increasing with increasing density of solids in said region, said flow-effecting means comprising means for continuously introducing liquid into said tank below said region, said teeter column means operating to accumulate a classified fraction comprising faster settling solids at said region of the tank, a siphon conduit opening in said region and extending upwardly to an upper locality above said overflow level and then downwardly to a discharge region outside the tank below said overflow level, for removal of r a pulp of the aforesaid solids classified by said hindered settling, said upper locality of the siphon conduit being disposed below a level corresponding to the hydrostatic equivalent of a pressure in said tank region which corresponds to a predetermined density of solids in said region, an air vent in said siphon conduit at said upper locality, and valve means for closing and opening said air vent to initiate and interrupt continuous flow of pulp through said siphon conduit.

7. The apparatus described in claim 6 which includes means connected with said predetermined region of the tank and controlled in accordance with the pressure in said region, for controlling said valve means to effect continuous flow of pulp through said siphon conduit only when the pressure in said region has a predetermined value which corresponds to a solids density at least equal to the aforesaid predetermined density.

8. The apparatus described in claim 7 which includes means for continuously introducing supplemental liquid into said siphon conduit at a rate substantially less than the rate of liquid introduction by the first-mentioned liquid-introducing means, at a place in said siphon conduit intermediate the first-mentioned opening of the conduit and said upper locality, said place being substantially spaced from both said opening and said upper locality, for promoting initiation and maintenance of continuous flow of pulp through said siphon conduit when said valve means is closed.

9. The apparatus described in claim 8, wherein the means for controlling the valve means comprises a hydrostatic conduit opening into the aforesaid region of the tank and extending through an upper region above the aforesaid upper locality, said hydrostatic conduit receiving liquid from the tank to a level hydrostatically corresponding to the pressure in said region, and means adjustably disposed at said upper region and controlled by the level of liquid in said hydrostatic conduit, for controlling the valve means to close the same only when the liquid in the hydrostatic conduit exceeds a predetermined level.

10. The apparatus described in claim 6, wherein said siphon means comprises a structure of successive pipe lengths having progressively smaller diameters from the opening in said predetermined region of the tank to the 12 downwardly extending portion of said siphon conduit outside the tank.

11. In hydraulic sizing apparatus, in combination, tank means having an overflow level and comprising teeter column means, siphon means comprising conduit structure opening into the tank means at a lower region of said teeter column means and extending upwardly to an upper locality above said overflow level and thence downwardly to a discharge locality outside the tank means and below said overflow level, for removing, in pulp form, solids classified in settling rate by said teeter column means, said teeter column means comprising means at the lower region thereof for introducing liquid to provide hindered settling in and above said lower region, for accumulatting faster settling solids at said lower region in the form of a pulp of said solids having a pressure which is sufliciently higher than the static head of liquid alone below said overflow level, as to elevate liquid in said conduit structure to said upper locality, and said siphon means comprising a vent in the conduit at said upper locality above the overflow level, and valve means for opening and closing the vent, correspondingly to initiate and interrupt continuous flow of pulp through the conduit structure.

12. The apparatus described in' claim 11, which includes means extending to said lower region of the teeter column means and responsive to the presence of pulp therein having a density of solids which affords the aforesaid pressure higher than the static head of liquid alone, for controlling the aforesaid valve means to efiect continuous flow of pulp through the siphon conduit structure only when the said density in the lower region of the teeter column means exceeds a predetermined value.

13. The apparatus described in claim 11, which includes means for introducing supplemental liquid continuously K into said siphon conduit structure at a place between its opening into the teeter column means and the aforesaid upper locality, for increasing liquid supply in the siphon means to promote initiation of siphon action.

14. The apparatus described in claim 11, which includes means for introducing supplemental liquid continuously into said siphon conduit structure at a place between its opening into the teeter column means and the aforesaid upper locality, for increasing liquid supply in the siphon means to promote initiation of siphon action, and means extending to said lower region of the teeter column means and responsive to hydrostatic pressure at said region, for controlling the aforesaid valve means to effect continuous flow of pulp through the siphon conduit structure only when the hydrostatic pressure at said lower region of the teeter column means exceeds a predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS 236,671 Cochrane Jan. 18, 1881 880,430 Veitch Feb. 25, 1908 1,490,420 Elder Apr. 15, 1924 1,512,159 Brinton Oct. 21, 1924 1,637,625 Shaw Aug. 2, 1927 1,716,228 Home June 4, 1929 1,959,212 Miller May 15, 1934 2,025,412 Handy Dec. 24, 1935 2,037,761 Coe Apr. 21, 1936 2,105,126 Pellett Jan. 11, 1938 2,124,343 Burroughs July 19, 1938 2,125,663 Wuensch Aug. 2, 1938 2,131,743 Loughridge Oct. 4, 1938 2,151,175 Wuensch Mar. 21, 1939 2,293,033 Mead et al Aug. 18, 1942 2,358,181 Mead et a1. Sept. 12, 1944 2,410,637 Darby Nov. 5, 1946 2,425,551 McKay Aug. 12, 1947 2,590,756 Colin Mar. 25, 1952 FOREIGN PATENTS 254,473 Italy July 28, 1927 im uneg

Claims

1. HYDRAULIC SIZING APPARATUS COMPRISING, IN COMBINATION, MEANS PROVIDING A TEETER COLUMN FOR RECEIVING DIVIDED SOLIDS TO BE CLASSIFIED ACCORDING TO SETTLING RATE, SAID MEANS INCLUDING MEANS INTRODUCING LIQUID TO PROVIDE UPWARD FLOW IN THE COLUMN FROM THE FOOT THEREOF AND SAID TEETER COLUMN MEANS BEING ADAPTED TO ACCUMULATE SOLIDS OF PREDETERMINED FASTER SETTLING CHARACTERISTICS NEAR THE FOOT THEREOF, SAID TEETER COLUMN MEANS COMPRISING A TANK FOR THE TEETER COLUMN, HAVING MEANS PROVIDING AN UPPER LEVEL FOR LIQUID IN THE TANK, SIPHON MEANS OPENING INTO SAID TEETER COLUMN MEANS NEAR THE FOOT THEREOF FOR WITHDRAWING A PULP OF ACCUMULATED SOLIDS, SAID SIPHON MEANS EXTENDING THROUGH AN UPPER REGION ABOVE THE AFORESAID UPPER LEVEL AND THENCE TO A LOWER REGION WHICH IS BELOW SAID UPPER LEVEL AND OUTSIDE THE TANK, SAID SIPHON MEANS COMPRISING A CONDUIT OPENING FOR DISCHARGE AT SAID LOWER REGION, AND SAID SIPHON MEANS INCLUDING AIR VENT MEANS THEREIN CONTROLLABLE TO MODIFY THE FLOW OF WITHDRAWN PULP THEREIN, A HYDROSTATIC COLUMN'' OPENING IN SAID TEETER COLUMN MEANS NEAR THE FOOT THEREOF AND EXTENDING TO AN UPPER LOCALITY ABOVE SAID UPPER REGION, FOR RISE OF LIQUID IN SAID COLUMN TO A LEVEL MEASURED BY THE PULP DENSITY IN THE TEETER, COLUMN, AND MEANS ASSOCIATED WITH THE HYDROSTATIC COLUMN AND CONTROLLED BY THE LIQUID LEVEL THEREIN AND COMPRISING A VALVE FOR CONTROLLING SAID SIPHON FLOW-MODIFYING MEANS, TO PREVENT WITHDRAWAL OF SOLIDS, IN SAID SIPHON MEANS, THAT DEPART FROM THE SAID PREDETERMINED SETTLING CHARACTERISTS.