US2815716A - Grit pump for wet grit blasting machines - Google Patents

Description

Dec. 10, 1957 N. RANSOHOFF 2,315,716

GRIT PUMP FOR WET GRIT BLASTING MACHINES Original Filed July 8 1949 s Sheets-Sheet 1 Y INVENTOR.

A T TORNE Y5 Dec. 10, 1957 N. RANSOHOFF v 2,815,716

GRIT PUMP FOR WET GRIT Bus-rm; MACHINES Original Filed July 8, 1949 3 Sheets-Sheet 2 INVENTOR.

A-rroeue ys.

I Dec. 10, 1957 N. RANSOHOFF 2,815,716

GRIT PUMP FOR WET GRIT BLASTING MACHINES Original Filed July 8, 1949 3 Sheets-Sheet 3 INVENTOE I BYW W' 17E. 4 Wr-ILM i m'toeueys,

United States Patent GRIT PUMP FORWET GRIT BLASTING MACHINES Nathan Ransohoff, Cincinnati, Ohio, assignor to N.

Ransohotf, Incorporated, Cincinnati, Ohio, at corporation of Ohio Original application July 8, 1949, Serial No. 103,703,

now Patent No. 2,632,980, dated March 31, 1953. Divided and this application June 27, 1952, Serial No. 298,932

3 Claims. (Cl. 103-104) This invention relates to the art of surface treating work pieces by the projection of abrasive particles at high velocity. This technique is known generally as grit blasting and is employed for the purpose of improving surface texture or quality, and particularly for the purpose of removing surface scale or adherent dirt or particles as in the treatment of rough sand castings and the like. The present application is a division of the copending application of Nathan Ransohoff for Method and Apparatus for Wet Grit Blasting, Serial No. 103,703, filed July 8, 1949, now Patent No. 2,632,980. The present application relates particularly to the grit pump for advancing a mixture of grit and liquid to the grit projector as disclosed in the above noted patent.

In conventional grit blasting methods, the abrasive particles, either sand, metal fragments or metal shot are propelled at high velocity upon the work surfaces by means of a blast of air, or by means of a so-called slinger which projects the particles through its own speed of rotation. The operation of grit blasting is a dusty one. Particles of the abrasive impacted on the surface of the work piece loosen dirt or scale either by attrition or by dislodgement and dust is liberated which pervades the atmosphere adjacent the work surface. The operation usually is conducted in the chamber of a grit blasting machine which is provided with a suitable exhaust system, but even so, the liberation of dust is a nuisance and, when the dust is of silicious nature, the operator is exposed to the dangers of contracting silicosis.

Some grit blast machines have been built for the projection of a liquid slurry or suspension of abrasive upon work but in each instance of this sort, the abrasive particles are exceedingly fine, as for example, from 60 to 1200 mesh, the slurry being aspirated from a source of supply through an air blast nozzle. Such abrasive slurries are useful in the treatment of work surfaces to improve the surface texture or to remove light oxide films but the particles of such slurries are much too fine for use in the grit blasting of coarse castings or the like where removal of a substantial quantity of adherent sand or surface particles must be accomplished in a short period of time or where there isto be a material alteration of the work surface. The use of metallic grit of high specific gravity and large particle size in such methods has been totally impossible; for example, grit particles or fragments up to A; inch in average diameter are much too heavy and dense, to be aspirated through a nozzle in an air blast or liquid stream and, of course, such particles cannot be pumped by ordinary methods.

A principal object of the present invention has been to provide a pump adapted to form a mixture of grit particles and liquid and to advance such a mixture at a low rate of velocity which is sufiiciently high to keep theparticles in a state of apparent suspension. Thus, the term, dynamic suspension, as used in this'specification' and throughout the claims is intended to designate a condition of distribution of grit particles in liquid which willbe 2,815,716 Patented Dec. 10, 1957 maintained while the liquid is in movement. This stream moving at low velocity and keeping its particles in a state of suspension in so doing, is advanced by the pump to a projector which is effective for accelerating the velocity of the stream and the particles contained within it, up to the speed required for grit blasting. While it is not possible to pump a liquid containing large particles of grit at grit blasting speed because of the attrition of the particles upon the pump or any conduit through which they must pass, still it is possible and practical to deliver a mixture of grit and water or liquid in an appropriate state of suspension of the particles up to the point of projection at a low velocity and then to impart additional energy to the particles which is requisite for them to accomplish the grit blasting function. This procedure eliminates the abrasion or wear which would otherwise be involved and enables all of the advantages and efiiciency of a dry grit blast system to be obtained without the nuisance of dust. Furthermore, it is found that by conducting the blasting in the presence of liquid, at finer surface finish is produced.

To form the suspension, or more particularly, to advance a dynamic suspension of the particles or liquid, the present pump is somewhat akin to a centrifugal pump with provisions for introducing liquid and grit into it simultaneously. The pump is operated to advance the mixture at a low rate sufficient to dynamically suspend the particles and does not suffer excessive wear. From this point, the stream is advanced to a projector 'where the final high velocity is imparted to it. The projector either may be in the form of an air blast nozzle or in the form of a slinger wheel and both embodiments by way of illustration are shown in the accompanying drawing. Following projection of the stream upon the work surfaces, which is conducted in a chamberon account of splashing, the grit and the dislodged dirt fall and the water drains to a sump. The grit, of course, falls almost immediately to the bottom while the water is allowed to accumulate in a layer above it. The layer of grit at the bottom constitutes a supply awaiting recycling to the low velocity pump. Meanwhile, however, it has been discovered that'a substantial portion of the dirt dislodged from the work, in typical grit blasting operations, is sufficiently light in density as to form at least a temporary suspension in the water over the grit.

In common production operations, a system of the type just described would soon become overcharged with accumulated dirt since, in typical operations, the amount of dirt removed, for example as sand from a rough casting, is appreciable. However, in the present machine, a portion of the water accumulated over the grit is discharged into a settling or separatory apparatus where the suspended dirt is removed, as by common settling, from the water or liquid so as to leave the liquid in a relatively clean condition adapted to be recycled back to the machine. Thus, the clean suspension system and the dirt rem-oval system may be in communication with one another through the chamber or the sump of the chamber in which blasting is conducted, with the dirt separation system functioning to condition the water for reuse. The advantage of this arrangement resides in the fact that the liquid portion of the treatment media is not subjected to dilution through constant additions of make-up liquid to it. Hence, the concentration of any added chemical such as a rust inhibitor or the' like is not diluted.

The dynamic suspension "of grit particles and liquid is advanced by the pump to a throwing wheel or slinger mounted on a resilient structure, which permits the wheel to rotate at blastingspeed without'transmitting vibrations to the apparatus. The grit particles are discharged by a nozzle into the interior of the wheel which has -radial vanes, the grit particles being intercepted by theleading edges of the vanes which travel" substantially at the same rate as the particles, whereby the grit particles are accelerated uniformly as they are propelled outwardly by the vanes toward the periphery of the wheel. The work pieces are conveyed upon a rotary table relative to the blasting wheel so that the pieces are treated by advancing them through the grit blast stream. In this instance, there is provided also a flushing station which projects jets of the settled or clarified liquid upon the work surface after treatment, to remove the foreign materials dislodged by the blast stream. The sump, which is disposed beneath the table, is arranged to contain a mass of grit particles and water, preferably containing a rust inhibiting solution, to protect the cleaned work surfaces. Grit particles and liquid thus fall by gravity from the Work table to the sump for recirculation by the pump. In this form of apparatus, the work pieces are treated in batches for a time period as determined by the particular class of work, each piece of work being passed successively through the blast stream at a proper speed to obtain the desired result.

The apparatus is adapted for utilization in well known commercial machines such as rotary tumbling mills, either the batch or continuous type, and also machines of the class incorporating a conveyor arranged to advance the Work pieces through a treatment tunnel. As applied to rotary machines, one or more blasting wheels or other suitable projectors may be installed upon shafts extended into the tumbler so as to project grit streams upon the work pieces as they are agitated in the rotating tumbler or the wheel may be set to impel the grit into the open end of a tilted barrel. In conveyor type machines, one or more grit blasting wheels may be installed within the tunnel in positions to project the grit streams against opposite sides of the work pieces as they are advanced past the wheels by the conveyor. Also, Work may be treated by placing it in fixed position in the blast stream for a timed, treatment period or by moving the projector relative to stationary work pieces.

From the foregoing disclosure of the principles involved, and from the detailed description taken in conjunction with the drawings, those skilled in the art will comprehend readily the various modifications of which the invention is capable.

In the drawings:

Figure 1 is a side elevation of the machine illustrating the general arrangement of parts.

Figure 2 is a sectional view taken on line 2-2 of Figure 1, illustrating generally the internal structure of the machine.

Figure 3 is an enlarged fragmentary sectional view taken from Figure 2, detailing the relationship of the grit conveyor and the grit pump.

Figure 4 is a sectional view taken on line 4-4 of Figure 3, further detailing the construction of the grit pump.

The apparatus disclosed in the drawings represents one organization utilizing the present pump and constitutes a treating machine having a rotary table arranged to convey work pieces successively through a grit blast stream and a rinsing station where the work pieces are flushed with a liquid solution, preferably water, containing a rust inhibitor. The grit and liquid are stored in a sump beneath the work table and in a settling tank respectively and recirculated continuously by the grit pump to the grit wheel and by a liquid pump to the spray pipe.

The grit particles preferably consist of metallic particles such as steel or metal shot, having a density substantially greater than water and greater than non-metallic grit. the sump to be conveyed mechanically to the grit pump, whereas the scale and dirt form a sludge of lesser density which remains in suspension at least temporarily in the water.

Since it is necessary to flush the work pieces with relatively clean water after grit blasting, the sludge is These particles settle quickly to the bottom of removed by drawing the liquid from the upper portion of the sump and passing it through a settling apparatus for removing the sludge before conducting the liquid to the spray pipe. Thus, one supply of liquid is drawn directly from the sump to provide a carrier for the grit particles, while another portion is drawn from the sump and clarified before being recirculated to the rinsing station.

Described with particular reference to Figure 2 of the drawings, the apparatus in general consists of a treatment chamber 15 having a rotary work support table 16, a grit blasting wheel 17 arranged to propel a blast stream of grit particles upon the work pieces carried by the table, and a spray pipe 18 arranged to fiush the work pieces with jets of water or liquid solution after the grit blast treatment.

As above noted, the same solution preferably is used as a carrier for the grit particles and for the flushing treatment, there being provided a sump 19 in the base of the chamber for receiving the liquid and grit after passage over the work. The grit, which is considerably more dense than the liquid, settles almost immediately to the bottom of the sump after blasting to be recirculated to the blasting wheel. For this purpose there is provided a screw conveyor 20 in the sump bottom to feed the grit mechanically at a controlled rate to the grit pump 21 where it is mixed with liquid drawn from the sump and introduced into the pump, the liquid serving as a carrier so that the grit particles are conveyed with the liquid through a conduit to the blasting wheel.

The apparatus thus is provided with two separate circulatory systems, one system indicated generally at 22, being arranged to convey the mixture of grit and water from the pump to the blasting wheel and a second system, indicated at 23, arranged to draw off liquid from the upper portion of the hopper and to discharge the liquid into a settling apparatus for sludge removal, subsequently to be recirculated back to the spray pipe. The settling apparatus 24 is disclosed in the present instance as a pair of decanting tanks, although it is intended in connection with larger machines, to provide a sludge and sand removal apparatus having a mechanical conveyor passing through a settling tank for continuous operation.

In the present disclosure, the chamber 15 may be formed from sheet metal in the form of a square or rectangular housing having a pair of converging side walls 2525, forming the hopper or sump 19 which is generally V-shaped as viewed in Figure 1. The side walls form a conveyor trough 26 in which is rotatably mounted the conveyor screw 20, arranged to feed the grit particles to the grit pump 21 located at one end of the trough.

As viewed in Figure 2, the conveyor trough and screw are inclined downwardly toward the grit pump to facilitate movement of the grit particles. As shown, there is provided a well 28 rising from the grit pump and open to the sump to maintain a liquid level common to that in the sump to permit the grit to be fed directly by the conveyor into the grit pump. In operation a liquid passes with the grit into the the pump, and an additional supply of liquid is drawn from the upper level of the sump and discharged into the bottom of the pump to prevent any accumulation of grit in the pump bottom.

At the front of the housing, there is provided a door 30 for loading and unloading the work table and for general utility in operating and servicing the machine (Figure l). The door is supported at its upper end by a pair of inclined lugs 3131 welded or otherwise secured to the chamber adjacent the door opening (not shown). The door includes a pair of studs 3232 secured upon its upper edge and projecting outwardly from opposite sides and resting upon the lugs. The lower edge of the door is confined by a vertical flange (not shown) secured to the housing beneath the door opening and spaced from the housing so as to slidably confine the edge of the door between the flange and housing. In closed position, the

lower edge of the door is held against the housing by the flange and the upper edge by the inclined lugs 31. The door includes a handle 35 by which it may be lifted out of engagement with the lugs and flange and either removed entirely or swung to an open position for access into the chamber. Along the opposite sides of the door opening, there is mounted a pair of brackets 3636 angularly related to the housing and designed to maintain the door in an inclined position in front of the door opening with the lower edge of the door resting against the housing. During operation of the machine, the door is kept closed to prevent grit particles from being discharged from the machine, although for observation purposes, the machine may be operated with the door partially open, as above noted.

As shown, the machine is supported by vertical legs 37 formed preferably from angle irons, the upper ends of thelegs being welded or otherwise secured to the chamber as at 38. The lower ends of the legs are connected to a framework 39 which braces the legs and provides a support for the driving mechanism of the grit conveyor as hereinafter disclosed.

Grit conveying apparatus As illustrated in Figure 2, the sump 19' provides a common reservoir for a supply of grit particles indicated at 40 and the liquid, preferably consisting of water, indicated at 41, including a rust inhibitor compound. In operation, a continuous supply of grit is advanced by the conveyor to the grit pump 21 and, at the same time, a supply of liquid is drawn from the sump by conduit 42 and introduced into the bottom of the pump casing at the center thereof (Figure 1). The grit particles are fed into the center of the pump impeller from above by the conveyor, as illustrated in Figure 3. By operation of the impeller, the grit particles are intermingled with the liquid and discharged into the flexible conduit 43 which leads to the grit blasting wheel or slinger 17. The mixture is conducted through the conduit at a velocity sufficient to maintain the particles in dynamic suspension, but insuflicient to perform the blasting operation or to cause substantial wear upon the pump or conduit. The upper end of the conduit 43 passes through the housing and is connected to theblasting wheel nozzle in the manner shown in Figure 2.

Described in detail, the grit conveyor constitutes a spiral vane or screw which includes a shaft 44 having its opposite ends journalled in bearings 45 and 46. The shaft extends through the upper bearing45 and includes a sprocket 47 for driving the screw. Since bearing 45 is below the liquid level in the sump, it is provided with a packing gland to prevent leakage of liquid. The packing gland and bearing is a commercial product and, for this reason, is not disclosed in detail. The lower bearing 46 is mounted upon the top of the pump casing within the well 28, submerged in the liquid. Both bearings are provided with suitable seals to protect the bearing surfaces against the entry of grit particles and sand.

The driving apparatus for the conveyor screw preferably is a commercial variable speed unit mounted upon a base plate 48 supported by the legs 37 and framework 39 beneath the sump (Figures 1 and 2). The unit, in general, consists of a motor 50 having a variable diameter V-belt pulley 51 of conventional construction. The motor pulley 51 is connected by a V-belt to a V-belt pulley 53 mounted on the shaft of a speed reducer unit 54. On

the opposite end of the speed reducer, there is provided a sprocket 55 which is connected to the conveyor sprocket 47 by a chain 56. Conveyor speed is regulated by shifting the motor relative to the speed reducer unit. For this purpose, the motor is mounted upon an adjustable base 57 having a hand wheel 58 arranged to shift the motor relative to the speed reducer and thus to change the elfective diameter of the motor pulley. By virtue of the variable speed unit, the rate of grit feed to the blast wheel may be regulated according to the particular requirements of the operation.

The lower or discharge end of the conveyor screw feeds the gut in the presence of the liquid maintained above the pump, directly into the grit pump through an opening59 formed by a collar 60 mounted in the top wall of the pump casing (Figures 3 and 4.) Since the conveyor screw is provided with a single spiral vane 61, it will be evident that the discharge of grit will be intermittent, that is to say, there will be a concentrated discharge each time the trailing end of the vane makes one revolution through the lower Zone of the conveyor trough. In order to provide a continuous discharge, a device is provided which regulates the flow of grit particles by restricting the passage of material from the conveyor to t-he'grit pump. I

This device consists of a collar 62 welded or otherwise secured in the end wall 63 of the hopper and provided with a stationary control disk 64 secured within the collar and operating in conjunction with a disk 65 secured to and rotatable with the screw shaft 44. As shown in Figures 2 and 3, the rotary disk 65 includes blades 66 which are pitched in the same direction as the screw vane 61 while the blades 67 of the stationary disk are pitched in the opposite direction. The rotary blades 66 preferably have a collective pitch equal to one turn of the screw vane and the stationary blades have an equal pitch in the opposite direction. It is found that this arrangement effectively regulates the discharge of grit without building up back pressure against the conveyor screw.

Grit pump The grit pump consists of a circular casing 68 having a rotor or impeller generally indicated at 69, enclosed within the casing by end plate assemblies 70 and 71 (Figures 3 and 4). The casing 68 includes upper and lower circumferential flanges 72-72. The end plate assemblies are secured by means of bolts 73' passing through matching apertures located at spaced intervals around the circumference of the pump. The inner ends of the bolts are provided with nuts and washers 74 and 75. Each of the end plate assemblies 70 and 71 consist of a pair of metal plates 76 76 having a sheet 77 of rubber, synthetic rubber or the like interposed in compression between the plates.

The impeller consists of a pair of disks 78-78 spaced apart from one another and having a series of spiral vanes 79 interposed between the spaced plates and secured by welding. Above and below the respective plates, there is provided secondary sets of spiral vanes 80 and 81 which supplement the pumping action of the vanes 79. It will be noted that the collar 60 extends through a central opening formed in the top disk 78 of the impeller so that the material discharged from the conveyor passes through the collar directly into the pumping zone between the impeller disks for actuation by the inner or leading edges 82 of the vanes 79. As shown in Figure 4, the inner edges of vanes 79 and 80 terminate at the outside diameter of collar 60 while the inner ends 83 of the secondary vanes 81 extend inwardly to the hub 84 which is welded as at 85 to the lower impeller disk.

Liquid is introduced through the bottom of the pump through a pipe 86 connected to the flexible tube or hose 42, the opposite end of which communicates with the hopper at a point above the level of the grit mass but below the liquid level. The liquid flows into the pump casing and is impelled radially by operation of the lower vanes 81 to prevent accumulation of grit particles at the bottom of the pump. The mixture of grit and liquid introduced through the opening 59 also flows radially from between the impeller disks so that the grit particles are picked up by the moving stream of solution at the bottom of the casing and intermingled with it for discharge into the pump outlet 87. Outlet 87 constitutes a section of pipe generally tangent to' the pump impeller,

. the pipe being welded to an opening formed in casing 68. The casing includes a partition 88 at one side of the opening to complete the passageway from the pump casing to the outlet. The mixture of grit and liquid is conducted by the flexible conduit 43 from the outlet 87 upwardly to the grit blasting wheel. Pipe 86 preferably includes a fitting 89 including a valve 90 for draining the liquid from the pump.

The previously noted pump well 28 is in the form of a cylindrical shell formed of sheet metal and having its vertical edges 91 secured by welding to the end wall of the hopper. This structure provides a mounting for the pump, the upper plate 76 of the pump being secured to the lower edge of the shell by welding as at 92 (Figure 3.

The pump is driven by means of a vertical shaft 93 journalled in bearings 94-94' secured to the end wall of the chamber and driven by a motor 95 mounted near the'top of the chamber (Figure 1). end of the shaft 93 there is provided a V-belt pulley Upon the upper 96 connected by belts 97 to a V-belt pulley 98 mounted on the motor shaft. The lower end of the pump drive shaft passes downwardly through the well 28 and has its lower end keyed to the hub 84 of the pump impeller.

The grit impeller is detachably secured to the shaft '93- by a screw 99 passing through a segment 100 which is welded as at 101 to the inside diameter of the hub .84 (Figure 3 and 4). The segment fits into a notch 102 cut into the end of the shaft so as to key with the segment and provide a driving connection between the hub and shaft. The segment is formed most conveniently by cutting it from the end of the shaft so as to form the notch 102 in the shaft corresponding in shape to the segment. The segment then is welded into the hub as shown and is drilled to provide a hole for the screw 99, which is threaded into the shaft, preferably with the parts in assembly.

As explained above, the liquid enters the top of the pump by way of the well 28 and also is drawn from the hopper from a point above the level of the grit mass by the tube 42 and enters the bottom of the pump by Way of pipe 86. As the liquid enters the pump cham- -ber, the secondary sets of spiral vanes 80 and 81 create currents of liquid in the spaces between the impeller and top and bottom plates of the pump to prevent the grit, which is concurrently introduced into the top of the pump, from settling in the spaces between the impeller and pump housing. The velocity of the liquid is sufiicient to carry the grit particles in dynamic suspension through the discharge tube 43 to the grit blasting wheel.

The structure of the blasting wheel or projector does not form apart of the present application and therefore is not disclosed in detail. In general the wheel 17 is mounted upon a drive shaft 103 journalled in the upper 'portion of the chamber upon bearing blocks 104104, vone of which is mounted upon a frame 105. The drive nected to the delivery tube 43 extending from the grit pump. The nozzle is coaxial with the drive shaft and extends into the interior of the blasting wheel which is provided with vanes which project the grit particles at highvelocity upon the rotary work table 16. given size wheel, for example, the wheel is driven at approximately 4,000 R. P. M. to provide the require Ina blasting velocity.

During the blasting operation, the circular work table 16 is rotated by a friction pulley which is urged toward the periphery of the table by a spring actuated lever structure 111. The pulley is in driving connection with a vertical shaft 112 which rises to a speed reducing unit 113 mounted on top of the chamber. The speed reducer 113 is driven by a V-belt and pulley system 114 extending from the grit pump shaft 93 to the speed reducer and including a standard type of variable speed idler pulley 115 adjustably mounted on top of the chamher to regulate the speed of the table. The table is rotatably mounted upon a shaft 116 journalled in a pair of spaced bearings carried upon a frame 117 extending crosswise of the chamber.

After being projected from the blasting wheel to the work pieces on the table, the grit and carrier liquid drain back to the sump where the grit particles settle to the conveyor trough. Operation of the spiral vane carries the grit particles back to the grit pump for recirculation with the liquid back to the blasting wheel.

The pump is effective to circulate and mix the suspension of liquid and grit particles under a speed of rotation which is sufficiently low to avoid rapid wearing of its surfaces by impingement of the grit particles. However, the currents induced by the secondary vanes 80 and 81 at top and bottom are sufiiciently rapid to sweep the grit outwardly from these areas. Upon flowing outwardly beyond the circumference of the impeller, the secondary currents from above the impeller commingle with the main flow stream passing outwardly from between the impeller disks. The carrier liquid passing outwardly from beneath the impeller from the intake pipe 86 is discharged outwardly beneath the main mass of grit particles and aids in suspending the particles dynamically as they advance toward the pump outlet. After advancing through the outlet and conduit, the stream flows under sufficient velocity to maintain the grit particles in suspension.

Having described my invention, I claim:

1. A grit pump for mixing and advancing grit particles and carrier liquid with the grit dynamically suspended in the liquid comprising, a cylindrical pump casing disposed upon a generally vertical axis and having a peripheral outlet passageway, an upper and lower horizontal closure plate secured to the opposite ends of the casing, a rotary pump impeller in the casing comprising an upper and lower impeller disk spaced apart from one another and spaced inwardly from the upper and lower closure plates, an open cylindrical feed collar concentric with said vertical axis, said collar passing downwardly through the upper closure plate and through the upper impeller disk into the space between the impeller disks, a vertical rotating drive shaft secured to the lower impeller disk and rising upwardly through feed collar on said vertical axis, said shaft rotating the impeller and delineating an annular intake passageway in combination with said collar, said annular intake passageway having an area greater than the area of the outlet passageway and advancing liquid and grit particles between the disks, a series of internal impeller vanes mounted between the spaced impeller disks having leading edges adjacent the periphery of the cylindrical feed collar and intercepting the liquid and grit particles discharging radially from the said annular passageway, said impeller vanes spiraling outwardly and rearwardly with respect to the direction of rotation of the impeller and discharging the liquid and grit horizontally to the pump casing at a velocity sufficiently low to preserve the pump surfaces from the abrasive action of the grit, and a series of secondary impeller vanes mounted upon the lower surface of the impeller disk, the lower closure plate having a secondary liquid intake passageway advancing liquid to the space between the lower closure plate and impeller disk, the secondary impeller vanes discharging the secondary liquid horizontally below the mixture discharged by the internal vanes, the combined volume discharged by the internal vanes and secondary vanes in 9 relation to the area of the outlet passageway accelerating the flow stream through the outlet passageway to a discharge velocity greater than the velocity of the mixture passing through the said annular passageway and through the pump, said discharge velocity being sulficient to maintain the grit particles in dynamic suspension.

2. A grit pump for mixing and advancing grit particles and carrier liquid with the grit dynamically suspended in the liquid comprising, a cylindrical pump casing disposed upon a generally vertical axis and having a peripheral outlet passageway, an upper and lower horizontal closure plate secured to the opposite ends of the casing, a rotary pump impeller in the casing comprising an upper and lower impeller disk spaced apart from one another and spaced inwardly from the upper and lower closure plates, an open cylindrical feed collar concentric with said axis, said collar passing downwardly through the upper closure plate into the space between the impeller disks, the cylindrical intake collar having an inside diameter at least twice the inside diameter of the said outlet passageway, a vertical rotating drive shaft secured to the lower impeller disk and rising upwardly through feed collar on said vertical axis, said shaft rotating the impeller and delineating an annular intake passageway in combination with said collar, said annular intake passageway having an area greater than the area of the outlet passageway and advancing liquid and grit particles between the disks, 2. series of internal vanes mounted between the spaced impeller disks having leading edges adjacent the periphery of the cylindrical feed collar and intercepting the liquid and grit particles discharging radially from the said annular passageway, said impeller vanes discharging the liquid and grit horizontally to the pump casing at a rate below the efiective abrading velocity of the grit, thereby preserving the pump surfaces, and a series of secondary impeller vanes mounted on the lower surface of the impeller disk and spiraling outwardly and rearwardly in the same direction as the internal vanes, the lower closure plate having a secondary liquid intake passageway concentric to said vertical axis and advancing liquid to said passageway into the space between the lower closure plate and impelled disk, the impeller having a horizontal surface residing above the secondary liquid intake passageway and providing a restricted radial passageway for the secondary liquid, the secondary impeller vanes having leading edges adjacent said restricted passageway and discharging the secondary liquid horizontally below the mixture discharged by the internal vanes, the combined volume discharged by the internal vanes and secondary vanes in relation to the area of the outlet passageway accelerating the flow stream through the outlet passageway to a discharge velocity which is substantially greater than the velocity of the mixture passing through the said annular passageway and through the pump suflicient to advance the mixture with the grit particles in dynamic suspension.

3. A grit pump for mixing and advancing grit particles and carrier liquid with the grit dynamically suspended in the liquid comprising, a cylindrical pump casing disposed upon a generally vertical axis and having a peripheral outlet passageway, an upper and lower horizontal closure plate secured to the opposite ends of the casing, a rotary pump impeller in the casing comprising an upper and lower impeller disk spaced apart from one another and spaced inwardly from the upper and lower closure plates, an open cylindrical feed collar concentric with said vertical axis, said collar passing downwardly through the upper closure plate and through the upper impeller disk, the cylindrical intake collar having an inside diameter at least twice the inside diameter of the said outlet passageway, the feed collar having a lower discharge end residing in a plane midway between the upper and lower impeller disks, a vertical rotating drive shaft secured to the lower impeller disk and rising upwardly through feed collar on said vertical axis, said shaft rotating the impeller and delineating an annular intake passageway in combination with said collar, said annular intake passageway having an area greater than the area of the outlet passageway and advancing liquid and grit particles between the impeller disks, a series of internal impeller vanes mounted between the spaced impeller disks, said vanes having leading edges adjacent the periphery of the cylindrical feed collar in position to intercept the carrier liquid and grit particles discharging radially from the said annular passageway, said impeller vanes spiraling outwardly and rear- Wardly with respect to the direction of rotation of the impeller and discharging the carrier liquid and grit particles horizontally to the pump casing at a rate below the effective abrading velocity of the grit particles, thereby preserving the pump surfaces, and a series of secondary impeller vanes mounted upon the lower surface of the impeller disk, said secondary impeller vanes having a width equal to at least one third of the width of the internal impeller vanes, the secondary impeller vanes spiraling outwardly and rearwardly in the same direction as the internal vanes, the lower closure plate having a secondary liquid intake passageway concentric to said axis advancing liquid to the space between the lower closure plate and impeller disk, the secondary impeller vanes having leading edges adjacent said passageway and discharging the secondary liquid horizontally below the mixture discharged by the internal vanes, the combined volume discharged by the internal vanes and secondary vanes in relation to the area of the outlet passageway accelerating the flow stream through the outlet passageway to a discharge velocity which is substantially greater than the velocity of the mixture passing through the said annular intake passageway and through the pump impeller sufficient to advance the mixture with the grit particles in dynamic suspension.

References Cited in the file of this patent UNITED STATES PATENTS 1,462,786 Cleveland July 24, 1923 2,077,637 Minich Apr. 20, 1937 2,170,831 Minich Aug. 29, 1939 2,207,317 Gear July 9, 1940 2,265,758 Klosson Dec. 9, 1941 2,376,639 Unger Mar. 22, 1945 2,462,480 Eppler Feb. 22, 1949 2,613,482 Hamacher Oct. 14, 1952 2,632,980 Ransohofl Mar. 31, 1953

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