US2581504A

US2581504A - Centrifugal pump

Info

Publication number: US2581504A
Application number: US133336A
Authority: US
Inventors: Elmer R Wilfley; Jr John L Aldred
Original assignee: Wilfley & Sons Inc A
Current assignee: AR Wilfley and Sons Inc
Priority date: 1949-12-16
Filing date: 1949-12-16
Publication date: 1952-01-08
Anticipated expiration: 1969-01-08

Description

Jan. .8, 1952 E. R. wlLFLEY ETAL. 2,581,504

CENTRIFUGAL PUMP Filed Dec. 1G, 1949 5 Sheets-Sheet 1 BY John Aldred 1r.

ATTORNEY E. R. WILFLEY ETAL Jan. 8, 1952 CENTRIFUGAL PUMP 5 Sheets-Sheet 2 Filed Dec. 16, 1949 ATTORNEY Jan. 8, 1952 E. R. wlLFLEY Erm. 2,581,504

CENTRIFUGAL PUMP Filed Deo. 16, 1949 5 Sheets-Sheet ."5

Fig. 4.52

Fig. 5.

INVENTOR Elmer R. Wi|fley BY John L. Aldred jr.

mmm

ATTORNEY E. R. WILFLEY ETAL CENTRIFUGAL PUMP 5 Sheets-Sheet 4 Filed Dec. 16, 1949 INVENTOR Elmer R. Wilfley BY John L. Aldr'ed jr. mmwww Jan. 8, 1952 E. R. wlLFLr-:Y l-:TAL

CENTRIFUGAL PUMP 5 Sheets-Sheet 5 Filed Dec. 16, 1949 lNvENroR Elmer R. Wilfley BY John L. Aldred 1r.

ATTO R N EY Patented Jan. 1.952

UNITED sTATEs yPATENT oFFlcE z,5s1,5o4

CENTRIFUGAL PUMP Elmer R. Wilfiey and John L. Aldred, Jr., Denver, Colo., assignors to A. R. Wiliey and Sons, Inc., Denver, Colo., a corporation of Colorado Application December 16, 1949, Serial No. 133,336

Claims. l

This invention relates to centrifugal pumps and in particular to that class thereof which avoid the use of a frictional seal or packing gland between the impeller shaft and the pump housing, to render such pumps serviceable for pumping corrosive liquids or liquids carrying grit or sand. Such pumps are usually referred to as sand or slurry pumps and an example thereof is shown in the U. S. Patent to Wilfley, No. 1,976,532.

That patent shows a sand pump in which the impeller-carrying shaft has a sleeve valve surrounding it that is shiftable in an axial direction upon the shaft to close and to open alternately an annular clearance between the impeller shaft and the surrounding portion of the pump housing. The sleeve valvel is normally held by spring pressure in sealing relationship with the housing when the pump is not operating. As soon as the impeller shaft starts rotating, centrifugally operated pivoted weights retract the sleeve valve from its seat against the pressure of the spring Where it remains while the pump is running. Leakage through the thus open annular clearance between the shaft and the housing is sought to be discouraged by an auxiliary impeller rotating coaxially with the impeller shaft to create hydraulic pressure that opposes the tendency of leakage of liquid or slurry through that clearance. Because of that function, the auxiliary impeller is herein referred to as a sealing impeller. When the pump is stopped, centrifugal force on the pivoted weights wanes with the result that the spring reasserts its pressure to shift the sleeve valve into position for closing the annular clearance between the shaft and the housing.

Such sealing impeller is shown generally in U. S. Patent No. 1,346,926 to Wilfley, with that impeller rotatable in a surrounding chamber.

This invention, while availing itself of teachings contained in these patents, embodies them in a sand pump of novel characteristics offering important functional and structural improvements.

An important object of this invention is to produce a sand pump of greater efiiciency than any of the aforementioned patented pumps per se. Without sacrificing the lbest features in them. The term efficiency is herein used in a somewhat specific sense denoting the ability of and purpose of the sealing impeller of discouraging or preventing entrance and entrainment of air into the pump during operation, inasmuch as such air entrainment adversely affects the capacity of 2 the pump efficiency especially when operating on a suction lift.

Therefore, this invention relates more particualrly to improvements in leak-sealing impeller devices as well as in improvements of the sealing effectiveness of such a pump.

Another object is to embody a sealing impeller in the sand pump in such a manner as to improve and facilitate the assembly of the pump.

In the pump disclosed in the Patent No. 1,346,926, the sealing impeller rotates in and is surrounded by an auxiliary chamber herein termed sealing chamber which at one side communicates with the interior of the pump housing and at the other side with the atmosphere. That is to say, that side of the chamber which faces the interior of the pump forms an annular clearance or passage around the impeller shaft and so does that side of the chamber which faces in the opposite direction, namely outwardly. These annular clearances then constitute respectively an inner passage and an outer passage, the inner passage communicating with the interior of the pump, and the outerpassage communicating with the outer atmosphere although automatically closed by a leakage-preventing sleeve valve whenever the impeller shaft stops rotating. The sealing impeller itself comprises a disc having blades or vanes extending radially upon each face of the disc. The vanes facing the interior of the pump housing have a shorter effective length than the vanes facing outwardly, and the set of shorter vanes will herein also be termed the inner vanes while the set of longer vanes will be termed the outer vanes. Both sets of vanes exert centrifugal forces upon a body of liquid in the chamber although in directions opposed to each other, in that the force exerted -by the inner blades opposes that exerted by the outer blades, the force from the outer blades however being in excess of the force from the inner blades because of the differential in elective length between the two sets of blades, the concept being that the force from the inner vanes would tend to push liquid outwardly from the pump housing, while a somewhat greater force from the outer vanes would tend to push the liquid inwardly into the pump housing.

According to the concept of operation of the patented sealing impeller atmospheric air seeks to enter the interior of the pump housing by way of passing from the side of outer vanes around the peripheral edge of the disc to the side of inner vanes, but this is to be counteracted, prevented or discouraged by the centrifugal force size-screening zone.

imparted to liquid or pulp in the chamber by the inner vanes. However, this condition is maintainable in a balanced manner only if, according to the concept of the patent, the outward force from the inner vanes is counteracted by the inward force from the outer vanes so that the resultant equilibrium of forces might maintain the desired annular body of sealing liquid or pulp around the marginal portion of the disc. The concept according to the patent is that with the centrifugal force imparted to the sealing liquid by the outer (longer) vanes being somewhat greater than that imparted by the inner v(shorter) vanes, atmospheric air enters the chamber only on the side of the outer vanes by interfacial contact with the liquid or pulp which on that side recedes towards the periphery of the disc although not exposing it. Indeed, if the pump and the sealing impeller were to function as proposed by the patent, the sealing liquid on the side of the outer vanes should recede to a point where a balance is reached between the pressure of the liquid and air on the side of the inner vanes.

It was expected that this patented bladed sealing impeller would stir liquid, suspended solids. and air in the chamber into such a churned mixture that the churned mass or pulp would act as a seal against air-leakage into the pump. But such was not the case to an extent to give assurance against such leaks, nor did the phenomenon of equilibrium develop to the extent expected. Therefore, it is an important object of this invention to improve upon that air-seal to make it more effective and dependable while combining it with the shiftable sleeve valve mechanism of the Patent No. 1,976,532.

This object is realizable by providing the sealing chamber with solids-screening means or passages for controlling the particle size or dimension of solids allowed to enter the chamber from the pump, as well as with relief duct means leading from the periphery of the sealing chamber into the inlet portion of the pump housing, and so proportioned relative to the screening passages that a suspension of substantially uniform density is maintained in the chamber for sealing purposes. The function of the screening means is to arrest and reject oversize solids to prevent them from reaching the blades of the sealing impeller disc. Such means may include satisfactorily successive and progressive screening zones including a primary size-selecting zone characterized by an annular ingress opening of predetermined size followed by a secondary sizescreening zone characterized by an annular throat. These means are exemplified by a chamber that is defined on its pump-end by a plate having an unular rib or ridge laterally extending toward the disc to form therewith thethroat of the secondary zone, that is a throat of liquid connecting an inner smaller annular pool of primary sized suspended solids entering it from the pump (through the ingress opening of the primary size-selecting zone) and an outer larger annular pool of such solids small enough to have passed through the primary size-selecting zone and then through the throat of the secondary This is accomplished by having the width of the ingress opening to the chamber a predetermined size and the width of the throat less than that of the ingress opening.

If suspended solids 'are continually supplied to the chamber, they will accumulatetherein and intimately displace the liquid until they ,dil the dilution of the suspended solids within the chaml ber. Such means are exemplified by an egress duct or relief duct leading from the chamber back to the inlet side of the pump with that duct carefully dimensioned so as to allow suspended solids from the chamber to pass therethrough at such a rate that the chamber is neither evacuated of its liquid nor has the concentration of its solids unduly increased. To that end, the egress duct must have its width or cross-sectional dimension greater than that of the throat and of the ingress opening but not large enough for the blades to pump liquid from the chamber at a rate faster than it flows into the chamber through the ingress opening and the size-screening throat. Again, the inlet end of the egress duct is placed adjacent the periphery of the sealing chamber and the duct extends generally radially of the chamber to insure bleeding off of suspended solids from the chamber back to the pump with sufficient centrifugal force to prevent plugging of the duct.

Thus, by the use and in the practice of this invention there is provided an annular turbulent pool of suspended solids in which the periphery of the bladed disc of the sealing impeller is submerged at all times during its rotation, with those solids controlled as to maximum size and with the density of the suspension maintained substantially constant with that of the suspension being pumped by the pump. The density of the suspended solids is also maintained on the suspension-receiving face of the disc while on the opposite face of the disc air is received which is also rendered highly turbulent by the longer blades on that face. The mass of turbulent air engages against the denser pool of suspended solids in which the periphery of the disc is submerged and is substantially repelled thereby. n other words, the air that is carried by the outer vanes is being separated centrifugally from the solids and liquid mixture. If the pump is operated with negative pressure at the inlet end, the air mass between the air-contacting face of the disc and the chamber will be greater in extent or in diameter than the extent of submergence of K the periphery of the disc. Reversely, if the pump is operated with positive pressure, the extent of the air mass Will be less than that of the extent of submergence of the disc. That is to say, for the seal to operate properly the diameter of the cylindrical air-liquid interface must be smaller than the diameter of a circle defining the outer ends or tips of the long vanes on the outer side of the disc, since these tips must be surrounded by liquid in order to enable them to maintain centrifugal action upon the liquid. However, the diameter of this interface will be greater when the liquid is supplied to the pump under a negative head than when it is supplied under a positive head.

While some of the features of this invention render it particularly useful in the handling of solids-liquid suspension by the pump, this does not exclude the successful handlingof liquids which are free of solids in a pump embodying the essence of this invention. i

In the Wilfley Patent No. 1,976,532, the pump housing comprises a main body portion through which .extends the free end of the impeller shaft, and e 4envier portion removable from the body portion for outwardly removing the pumping impeller from the free end of the shaft. The sealing impeller is formed by an inward hollow extension of the hub portion of the pumping impeller and has blades that extend from the inner face of the hollow of that extension. The outer face of this extension presents a complementary portion of the inner contour of the inlet end of the pump housing so these two impellers comprise a fairly complex assembly. When dismantling the pump, the pumping impeller and its unitary sealing impeller must be removed from y the free outer end of the impeller shaft and from `the pump housing in an outward axial direction, while the impeller shaft itself together with its sleeve valve mechanism must be removed axially in the opposite direction.

Furthermore, that pump includes a removable shaft-carrying component whose inner end lodges in and is carried by the pump housing through a sealing gland, while the outer end of that component is supported by the pump base. This shaft-carrying component comprises as one assembly a ilxed tubular shell in which the impeller shaft is journalled and a cage extendingfrom the pump-end of this shell into the intake portion of the pump housing so as to surround the sleeve valve mechanism. The cage in effect constitutes an inward extension of the shell and its free end represents that end of the shaft-carrying assembly that lodges in the pump housing. The free end of the cage is closed by an annular end plate surrounding the impeller shaft and presenting inwardly within the cage an annular seat for the sleeve valve while its outer face is formed with an annular recess into which extends the sealing impeller.

Therefore, in such a pump, only after the pumping impeller with its sealing impeller has been disconnected and removed from the free end of the shaft. can the shaft-carrying assembly be removed with its shell in the opposite direction from the pump housing. In other words, such a pump comprises as main assembly components: (a) the pump housing and base; (h) the unitary pumping and sealing impellers; and (c) the shaft-carrying assembly with its valve mechanism.

It is among the objects of this invention while improving the sealing effectiveness of such a pump, to also improve it structurally in such a manner as to facilitate its assembly and to render it more readily accessible; in short to provide an improved sealing impeller arrangement yet without requiring any substantial changes in the basic disposition with respect to one another of the main assembly components (a), (b), and (c), of the pump.

These objects are attainable by adding to the closure plate of the cage a contour-shaped plate such that between it and the closure plate there is formed an auxiliary annular chamber to surround a separate sealing impeller carried by the impeller shaft alongwith the pumping impeller. That side of the contour plate that faces the interior of the pump presents a fixed streamlined portion of the inner contour of the inlet portion of the pump, even though constituting a part of the shaft-carrying assembly l c) Thus the sealing impeller is held in place within its chamber and is made to rotate with the pumping impeller shaft by a coupling connection between it and the pumping impeller which latter is removably ilxed to the free end of the shaft. This wnnelwi between the pumping impeller and the sealing impeller establishes itself in the course of assembling the pump. That is, when the pumping impeller is disconnected and removed from the shaft, such removal will disconnect it from its driving engagement with the sealingimpeller. The sealing impeller in turn is then removable from the pump housing as part of the removable shaft-carrying assembly. In other words, the pumping impeller and. the sealing impeller interengage at their hubs which have interengaging complementary scalloped faces, that is one hub has a scalloped end which engages with an abutting complementary scalloped end of the other hub. And further, a cushioning annulus is interposed and compressed between these hubs.

The best embodiment of the invention now known to us has been chosen as an example to describe herein for illustrative, but not limiting. purposes, since modifications obviously can be made therein so long as they do not depart from the scope of the appended claims and their equivalents. That embodiment is illustrated in the accompanying drawings in which:

Fig. 1 is a part-sectional longitudinal side view of the pump unit showing the improvements in the sealing means within an improved structural environment.

Fig. 2 is a part-sectional view of the pump shown in Fig. 1, although exploded. Fig. 3 is an enlarged detail view of that portion of the pump unit which comprises the improved sealing means.

Fig. 4 is a view similar to Fig. 3, with pressure conditions indicated in the sealing chamber corresponding to a. highly negative pump inlet pressure.

Fig. 5 is a view similar to Fig. 3, with pressure conditions indicated in the sealing chamber corresponding to a less negative pump inlet pressure.

Fig. 6 is a view similar to Figs. 3, 4, 5, although further enlarged to illustrate more clearly the operating conditions, especially the screening conditions, in the chamber.

Fig. 7 is a sectional detail view of the sealing impeller.

Fig. 8 is a View of the sealing impeller taken on line 8--8 of Fig. 7.

Fig. 9 is a view of the sealing impeller on linel 9-9 of Fig. 7.

Fig. 10 is a view of the sealing impeller taken on line Ill-I 0 of Fig. 9.

Referring to Fig. 1 the invention is embodied' in a pump unit in which an impeller shaft I0 is rotatable in a stationary and generally tubular structure II which has its front end extending into and is supported by a pump housing I2 while its rear end is supported by a bearing lug I3' constituting an integral part of the rear end portion of a base I 4 of the pump unit. yIn fact this base Il is also integral with what constitutes the in take housing portion I 2a of the pump housing. A bearing cover I3a holds the tubular structure in place upon the bearing lug I3. A discharge housing portion I5 it attached to the intake housing portion I ia and surrounds an impeller I6 fastened to the front end of shaft I0. An intermediate annular housing portion I1 is interposed between the housing portions-I2l and I5 and is sealed against them as by rubber ringsr I8 and I9. The

20 while the intake neck for the intake housing .portion is not shown in the drawing. l The 'tubular structure II is sealed against thev 2| held by a gland 22 secured as by lugs 23 fastened by bolts 24 to the intake portion. The tubular structure is held against longitudinal displacement although longitudinally adjusted by a' stud 25 screwed into the bearing lug I3 and secured to the tubular structure by means of a bifurcated lug 26 extending integrally from the tubular structure as well as by means of a pair of lock nuts 21 and 28 tightened from opposite directions against the bifurcated lug. The tubular structure I I comprises what mav be termed a shaft-bearing section 29, a valve control section 30, and a sealing impeller section 9|. The shaft bearing section 29 is so termed because it comprises a tubular member 32 having a front roller bearing 33 and a rear roller bearing 34 in which bearings rotates the impeller shaft although secured against axial displacement. The valve control section 30 comprises a cage 35 fastened by flange and bolt connection 35=L to the front end of the tubular member 32, and has a bottom opening 36. This cage houses a centrifugally controlled automatic valve actuating mechanism collectively designated as M and which is known per se as in the pump unit of the aforementioned Wilfiey Patent No. 1,976,532. Such i mechanism comprises an annular sleeve valve 31`yvhich is slidable in axial direction upon the impeller shaft I so as to open or close an annular gap or clearance 38 (more clearly shown in Fig. 6) and defined by an annular closure plate P which surrounds the impeller shaft and is unitary with and fastened to the cage l35.

The sleeve valve member 31 is unitary With a bell-shaped member or shield 39 which in turn surrounds the valve-actuating centrifugal mechanism proper. The shield 39 is movably connected to the axially non-shiftable shaft ||l by means of annular diaphragm 49. That is to say, the outer edge of this diaphragm is connected internally to shield 39 as at 4|, while the inner edge of the diaphragm is connected as at 42 to a sleeve member 43 which in turn is xed to the shaft. This diaphragm 40 by reason of its deformability allows for axial movement of the valve member and shield as a unit relative to the shaft by action of pivotally movable centrifugal weight members 44. Each of these weight members (only one of which is visible in Fig. l) is movable about a pivot 45 mounted upon and unitary with the sleeve member 43 and thus with the shaft lll.

vHence when the shaft rotates the outer or weighted ends 44 of the weight members move outwardly away from the shaft while their inner ends 44b engaging the interior of shield 39 move the valve member 31 axially to open position against the pressure of a coil spring 46 which surrounds the shaft and which returns the valve member to closed position when the rotation of the shaft stops and the centrifugal effect of the weight members ceases.

The sealing impeller section 3| constitutes an annular chamber` 41 formed by the closure plate P and by what is herein termed a contour plate 48. Within this chamber rotates a sealing impeller 49 fixed to the shaft in a manner more clearly shown in detail Figs. 3 to 6. That is the hub 4i!a of this sealing impeller is connected to the shaft by being confined 4between the inner end of sleeve member 43 and the adjacent end portion llia of the hub of impeller i6. Both the hub of the sealing impeller and of the pump impeller have at their mutually adjoining ends a wave-like formeticn presenting scallops Si and Sz respectively which are complementary to each other in such a manner that scallops Si extend into the recesses between scallops Sz and vice versa so that the rotation or torque of the shaft I0 is transmitted through the impeller I6 to the sealing impeller 49 so that both impellers will rotate as a unit with the shaft. Between the two complementary scalloped faces as indicated by scallops S1 and S2 there is interposed an annular torque-transmitting filler member 5|! of rubber or similarly resiliently deformable cushioning material which renders unnecessary any accurate machining or interfitting between the interengaging hub portions of impellers and 49.

The sealing impeller section 3| with its sealing impeller 49 and its chamber 41 embodies certain features which more clearly present themselves in detail Figs. 3 to l0. Mainly these features involve the provision of an ingress duct 5| leading from the inlet side of the pump interior centrally into the chamber 41, and an egress duct 52 herein also termed a relief duct leading from the margin of chamber 41 back to the inlet side of the pump interior.

The sealing impeller 49 comprises a disc p0rtion 53 integral with the hub 49". At its outer face and facing away from the interior of the pump the disc portionhas integral therewith radial extending long ribs herein also called the long vanes 54 designated by their length L1. The vanes 54 alternated with wedge-shaped lugs 55 interposed between respective outer end portions of the vanes 54 and are `also integral with the disc portion 53. At its inner face, that is facing the interior of the pump, the disc portion has integral therewith radially extending short ribs herein also called the short vanes 56 designated by their length L2. The position of the long vanes relative to the short vanes radially is such that the short vanes start a distance di from the inner end and terminating a distance da from the outer end of the long vanes. Thus the length L1 of the long vanes represents the4 sum total of the length di-i-La-l-dz.

The contour plate 48 surrounds the impeller hub portion constituting therewith the annular ingress opening 5I which is characterized by a width w1. Facing the interior of chamber 41 the contour plate is formed with an annular rib 51 extending towards the disc portion 53 of the sealing impeller and terminating a distance wa therefrom which is characteristic of an intermediate passage 58 between the ingress and egress ducts of the chamber. The egress ducts 52 are formed in the marginal portion of the contour plate 48 and comprises a radially extending portion 52a and a horizontally extending portion 52". The egress ducts are also characterized by a-width w3. The width wi of ingress duct 5| is smaller than the width wz of the intermediate passage 58, and width w3 in turn is smaller than wz. In this Way if the pump handles a pulp or liquid-solids mixture containing coarse and fine solids, the ingress opening will permit the passage therethrough only of a fine fraction into the sealing chamber 41. In the course of operation this ne fraction will pass from the central part to the outer parts of chamber 41 by way of the second or intermediate passage 58, and finally leave the marginal portion of the chamber 41 by way of the egress ducts 52. In this way a certain portion of solids-carrying liquid of suitable characteristics is allowed to circulate within the pump with respect to keeping the coarse particles ofthe pulp out of the sealing chamber 41 has been illustrated by indicating the mixture of solids entering, the pump as being characterized by coarse particles 50 and ne particles 5l, the fine particles only being allowed by reason of the width w1 to enter into and pass through the sealing chamber 41.l

Operation of the sealing impeller section As the pump starts running the valve controlled mechanism M acts to shift the valve member 31 outwardly and away from its seat on plate P, thus shifting it from its Fig. 3 (closed) position to its Fig. 6 (open) position. At the same time the sealing impeller 49 makes its action felt upon the liquider liquid-solids mixture that iills the sealing chamber 41 by imparting thereto centrifugal effects which cause an annular body of sealing liquid to form and to be maintained in the sealing chamber substantially as represented in Fig. 6 which body of liquid surrounds and immerges the marginal portion of the disc 53 of the sealing impeller. As a result of the interaction of hydrostatic pressures and centrifugal forces upon the liquid in chamber 41 there establishes itself an equilibrium manifesting itself in the fact that a portion of the outer face F1 of the sealing impeller is exposed to the atmosphere through the valve gap 38, while the peripheral portion and the opposite or inner face Fa are surrounded and contacted -by the liquid. Under operating conditions assumed to exist according to Fig. 6 the extent of exposure to air of face F1 is indicated by an area of the diameter D1 Which is smaller by the differential 2A than the diameter D: of the disc 53. Thus at its outer face the 'disc is immersed to a depth A representing the seal proper whereby entry of atmospheric air into the pump is. prevented. While the extent of disc immersion A shown in Fig. 6 corresponds to or represents a given set bif operating conditions, these conditions may allowed to vary within certain safe limits in accordance with a variation of the diameter D1.- Thus for a given pump there exists a latitudeconcerning variations of its operating conditions within which the liquid seal will function properly, such variations being mainly due to differences in the pressure under which the liquid is being supplied to the pump and which is herein briefly termed the supply pressure. 'That is to say, the supply pressure and therefore the extent of immersion A of the disc 53 may be allowed to vary provided that the marginal portion of the disc does not become denuded of sealing liquid and. on the other hand, provided that the sealing liquid is not allowed to cover so much of the outer face F1 of the disc as to risk its escape through the valve gap 38. Such safe limits in terms of diameter of the exposed portion of the face F1 of the disc are indicated in Figs. 4 and 5. Fig. 4 indicates a maximum safe diameter D3 corresponding to a relatively lower supply pressure while Fig 5 indicates a minimum safe diameter D1 corresponding to a relatively higher supply pressure. Again, the range of these limits can be altered by a change in the relative lengths L1 and L2 and relative positions of the impeller vanes 54 and 55.

The function of the sealing impeller is of especial significance as initially pointed out when the supply pressure is negative, that is when the pump operates under a suction lift. Let it be assumed then that the Fig. 6 condition representssuch a case. Withfhydraulic operating equilibrium set up in the sealing chamber 41 thereis established an air space A atthe outer face of the sealing impeller which air space isi' `definable by the circular area corresponding to diameter D1 and by a cylindrical area C representing the air liquid interface. Indeed, the centrifugal force which tends to compress the annular liquid sealing body in chamber 41, by its very compression also rejects air that might have gotten entrapped in the liquid, this diametrically maintaining the interface C substantially sharply as such. Y

The equilibrium conditionswhich maintain the annular body of sealing liquid around the margin of the disc 53 are due to the effect of the vanes 56 at one side of disc 53 being shorter than the vanes 54 at the other side of the `disc-- in other words, due to the chosen ratio of lengths Li/Ln of the vanes as well as. due to the disposition radially of the two sets of vanes relative to each other. Consequently, the centrifugal force imparted to the water by the shorter vanes is less than although counteracting that imparted by the longer vanes, the respective ducts of the centrifugal forces exerted by the two sets of vanes being indicated as by the arrows R1 and Rz in Fig. 6. Atmospheric air communicating with the air space A through the valve gap 38 has the tendency to enter the inlet side of the pump housing in response to the negative supply pressure or suction. therein, .but is prevented from doing so by the counteracting centrifugal force imparted to the sealing liquid by the shorter vanes. In other words, since the centrifugal force Rz is greater than the opposed centrifugal force R1 air enters the space A following the centrifugally receding liquid at the outer face of disc 53 until a balance is reached between the combined pressures of water and of air at the outer face F1 of disc 53 and the water pressure at the opposite or inner face F: of the disc. In this way atmospheric air is prevented from passing from the outer face F1 past the periphery of disc 53 to the inner face F2 thereof due to the annular body of sealing liquid surrounding the periphery of the disc. Hence, the very rotation of the impeller shaft while holding the valve member 31 in its open position, also hydraulically seals the inlet side of the pump housing against entrance of air even though the pump may have to rely upon the suction tto drawthe water or liquid-solids mixture into the pump.

It should be understood that entrained air is centrifugally separated from the liquid or pulp by the action of the long vanes of the sealing impeller so that no air by way of entrainment in thef liquid will reach the intake side of the pump and impair the suction lift thereof. Furthermore, the diameter D1 of the air-liquid interface C must be no greater than the diameter D2 which denes outer tips of the long vanes 54, since at least these tips must be immersed in or be surrounded by liquid in Yorder that centrifugal action upon the liquid and the formation of the annular body of sealing liquid may be sustained in the sealing chamber. However, the air space diameter D1 will be greater when the pump operates under a suction lift, that is negative supply head, than it will be with a positive supply head.

The ability of the short and the long vanes of the sealing impeller to maintain a liquid seal against a negative or a positive supply head depends upon their respective tip radii represented by diameters Dz and D respectively as well as.

upon their respective lengths L1 and Lz. By varying these structural factors for a given R. P. M. of the pump a seal to suit various supply pressure conditions results. For instance, ii a liquid seal were required against a highly negative supply head for a given R. P. M., the diameter D5 of the short vanes would be increased to a maximum as well as its length Lz thus increasing their pumping effect, while the dimension of the long vanes remain as is. If the seal were to be for a highly positive supply head, the pumping effect of the short vanes would be minimized to the point that only the surface roughness of the face Fz of the disc remained to produce a slight pumping effect, so that substantially theI full length of the long vanes Would remain effective in producinga pressure to balance the intake pressure of the pump.

For practical purposes. for example, three different combinations of lengths of the vanes may be provided, namely one for a high positive intake head, one for a negative intake head, and an intermediate one for a normal or average intake head. The variations in proportioning will lie in the dimensionng of the short vanes for given dimensions of the long vanes.

Fig. 6 represents the pump as handling a liquidsolids mixture or pulp containing relatively coarse solid particles designated as a group by the letter E, along with relatively finer particles designated as a group by the letter Ez. The action of the sealing impeller causes a quantity of pulp from the intake side of the pump to be recirculated through the sealing chamber, the pulp entering through the ingress duct 5| and returning to the intake side through the egress openings.

In considering the functioning of this recirculation of pulp through the sealing chamber, a distinction is to be drawn as between the respective widths and the through-flow areas of the ingressand egress-ducts. The egress area should not be so large that the

vanes

54 and 56 will pump liquid through that area faster than it enters through the ingress area. Indeed, the proportioning oi these areas should be such that the sealing chamber and sealing vanes have a continual supply of pulp substantially free of entrained air to work on. `Yet, the width w3 of the egress duct should be greater than the width wz of the intermediate passage 58 as well as greater than the width w1 of the ingress duct. The width wz in turn should be greater than width w1. Width w1 again is such that it Will selectively admit into the sealing chamber only smaller size solids Ez, the ingress duct thus in eifect constituting a primary sizing screen, While the width wz constitutes a secondary screen for sizing of particles after they have passed through the ingress duct. The widths wz and w1 represent the clearance between stationary and rotary parts, so that particles entering these clearances encounter considerable relative velocity as between the side walls of these clearances. If particles should find their way into these clearances of such size that would tend to stick or clog therein, the relative motion between the side walls would abrade the particles to such size that they would pass through. Therefore, as the clearances wz and wi are less than the clearance wa, the particles will pass through the egress ducts, being carried by liquid passing through the sealing chamber. Admittingto and recirculating through the sealing chamber a thus sized pulp fraction containing finer particles to the exclusion of the coarser ones insures smooth and uncongested operation of and less wear and tear upon the sealing chamber and the sealing impeller.

We claim:

1. A centrifugal pump having a pump housing and a pumping impeller carried by a rotatable shaft extending at one end into the pump housing, an auxiliary impeller disc on the shaft with blades laterally extending from each face of the disc, an annular chamber surrounding the auxiliary impeller having restricted ingress opening thereinto around the shaft from one direction for suspended solids from the pump and from another direction for air from outside the pump housing together with an egress duct leading back to the pump housing from a point farther away from the shaft than the ingress opening.

2. Apparatus according to claim 1, wherein the blades on the face of the disc nearest the pumping impeller are shorter than the blades on the other face and between the shaft and the inner ends of the shorter blades the chamber narrows toward the disc to provide a solids-screening passage for rejecting oversize suspended solids from reaching the shorter blades.

3. Apparatus according to claim 1, wherein the blades on the face of the disc nearest the pumping impeller are shorter than the blades on the other face and between the shaft and the inner ends of the shorter blades the chamber narrows toward the disc to provide a solids-screening passage for rejecting oversize suspended solids from reaching the shorter blades with the width of that passage being less than that of the ingress opening for suspended solids.

4. Apparatus according to claim 1, wherein the blades on the face of the disc nearest the pumping impeller are shorter than the blades on the other face and between the shaft and the inner ends of the 'shorter blades the chamber narrows toward the disc to provide a solids-screening passage for rejecting oversize suspended solids from reaching the shorter blades with the width of that passage being less than that of the ingress opening for suspended solids while the width of the egress duct is greater than that of the ingress opening.

5. Apparatus according to claim l, wherein the blades on the face of the disc nearest the pumping impeller are shorter than the blades on the other face with suspended solids being supplied to the shorter blades from the suspended-solids ingress opening while air is supplied to the longer blades from the air ingress opening whereby the chamber is lled with an agitated pool of suspended solids from which a quantity of such mixother face and between the shaft and theinner ends of the shorter bladesthe chamber narrows passage with a. largerpool of screened suspendedv solids enclosing the periphery of the disc -to which air is supplied past the longer blades on the disc.

7. A centrifugal pump having a pump housing supported from a base and a pumping impeller carried by a rotatable shaft extending at one end into the pump housing and at its other end supported in a tubular shell mounted from the base, automatically shiftable valve means between -the shaft and the pump housing for sealing space therebetween when the pump stops and opening it when the pump starts, an auxiliary impeller disc on the shaft between the valve means and the pump housing\with blades laterally extending from each face ofthe disc, and an annular chamber surrounding the auxiliary impeller having restricted ingress opening thereinto around the shaft from one direction for suspended solids from the pump and from another direction for air from the valve means together with an egress duct leading back to the pump housing from a point farther away from the shaft than the ingress opening.

8.Apparatus according to claim 7, in which the pump impeller and the auxiliary impeller have inter-engaging hub portions for jointly rotating with the shaft.

9. A centrifugal pump according to claim 7. in

shiftable in the tubular structure with a pump impeller carried by and fastened to the outer free end of the shaft surrounded by the housing, and further having automatically actuated sealing valve means for automatically opening and closlng an annular gap between the shaft and the I housing which comprise an annular valve member axially shiftable upon "the shaft forV opening and closing the gap and oentrifugally actuated mechanism surrounding the shaft and disposed within the inner end portion of the tubular structure 'c for shifting the valve member to automatically open and close the gap when the pump starts and stops respectively, said pump further having auxiliary impeller means rotating with the impeller shaft to counteract leakage through the gap; characterized by the fact that the tubular shaft-carrying structure has at its extreme inner end an annular chamber having a main annular which the pump impeller and the auxiliary im-V peller have inter-engaging hub portions for jointly rotating both impellers, with the addition of an annular member of resiliently deformable rubber-like material interposed and compressed between the interengaging hub portions.

10. A centrifugal pump having a base member, a pumphousing mounted upon the cuter end of the base member, a substantially tubular shaftcarrying structure having its outer end supported upon the outer end ofthe base member and its inner end supported in and by the inlet portion of the housing and in sealing relationship therewith. an impeller shaft rotatable and axially nonwall'portion providing a seat for the valveI member, and a complementary annular wall portion constituting a part of the inlet portion of the housing and presenting a concave contour merging with the inner contour of said inlet portion; and that the auxiliary impeller means comprise an impeller member rotating in the annular chamber and constituting with the shaft and with the tubular structure an assembly unit removable as such from the inlet portion of the pump housing.

y ELMER a. WniFLnY.

JOHN L. Amann, JR. REFERENCES CITED The 'following references are of record in the ille of this patent:

UNITED STATES PATENTS