CA2159650A1 - Toric pump - Google Patents

Abstract

A regenerative toric pump in which undesirable noise generation and leakage through clearance gaps between the impeller and housing is minimized includes an impeller having vanes lying in general planes radiating from the impeller axis disposed at variable spacings from each other in a geometrically balanced pattern. Recesses in one of opposed side surfaces on the impeller and housing are arranged in a pattern such as to minimize leakage through the clearance gap between those surfaces from points in the pump chamber which are at different pressures.

Description

TORIC PUMP

R~K~ROUND OF THE lNv~llON

The present invention is directed to a toric pump having an improved impeller which minimizes internal =leakage through the clearance gap between the impeller and pump housing and which minimizes the noise generated by operation of the pump.
Toric pumps of the type with which the present invention is concerned employ a disk like impeller having a series of radial vanes mounted around its periphery.
The opposed side surfaces o~ the impeller are flat, except for pockets between the vanes, and the impeller is mounted within a pump housing having an internal chamber having opposite sides surfaces and a peripheral sur~ace which closely encloses the impeller but allows suf~icient clearance such that the fluid can exit the impeller radially and then turn ~orward or backward into the internal pump chambers of the housing. The chamber walls are formed with an internal pump chamber or passage extending along an annular path in operative relationship with the path of the impeller vanes at a constant radial distance from the impeller axis from an inlet at one end of the toroidal passage to an outlet at the opposite end.
The circumferential extent of the toroidal passage around the pump axis is less than 360~, and between the ends o~

-the passage a relatively narrow portion o~ the chamber side wall extends across the annular region traversed by the toroidal chamber. This portion of the chamber side wall is called the stripper and the stripper ~unctions to de~lect ~luid being impelled through the pump chamber by the impeller vanes into the pump outlet instead o~ being pumped back to the inlet.
During operation o~ the pump, as each vane advances past the outlet end o~ the pump chamber to -cross the stripper, the sudden reduction in the cross sectional area o~ the chamber through which the vane is moving generates a discontinuity in the ~luid flow. Such a discontinuity occurs each time a vane passes across an edge o~ the stripper and, there is thus a generation o~ a cyclic change of resistance to the rotation o~ the impeller.
Where the vanes are equally spaced around the impeller periphery, the ~requency o~ this cyclic reaction is directly proportional to the rotative speed o~ the impeller, and at certain critical speeds, structural resonances or harmonics may develop which generate noise.
It has been recognized in the prior art that this problem may be solved to some extent by varying the vane spacing around the periphery o~ the impeller. However, variable vane spacing usually results in the creation o~ at least some rotor imbalance which in turn leads to problems potentially more serious than undesirable noise.

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A second problem encountered by pumps o~ types described above results ~rom the ~act that a slight clearance or gap must exist between the stationary pump housing sur~aces and the adjacent rotating sur~aces o~ the impeller in order that the impeller can ~reely rotate relative to the housing. Those portions o~ the chamber side sur~aces and the opposed side sur~aces of the impeller which are located radially inwardly o~ the toroidal pump chamber present a gap which extends the entire length o~ the radially inner side o~ the circum~erentially extending pump chamber. Pressure progressively increases in this chamber ~rom the inlet end to the outlet end, and the clearance gap provides a path ~or leakage o~ ~luid ~rom high pressure regions o~ the chamber to regions o~ lower pressure. Where the ~luid being pumped is o~ low viscosity - i.e., air for example -this leakage can be substantial and substantially reduce the ~low delivered by the pump.
Prior art attempts to employ a labyrinth type seal to reduce this leakage have not, in general been successful as demonstrated by the ~act that very ~ew, i~ any, commercially available regenerative pumps employ such seals. Labyrinth seals rely upon a series o~ restrictions separated by expansion chambers which are intended to enable the ~luid entering the chamber to expand to an increased volume or bulk which is in theory more di~icult to pass through the next ~ollowing restriction. Where the ~luid is o~ low compressibility, such as a liquid, no expansion takes place and the presence o~ the expansion chambers reduces the area available ~or restriction, thus reducing the e~ectiveness o~ the seal. Where the pump o~
the type described above is employed to pump gasses, the gasses are~highly compressible, but the pumps typically develop only a relatively small pressure di~erential between the inlet and outlet. Because o~ the relatively small di~erential between the density o~ the compressible ~luid at the inlet and its density at the outlet is present, there is little opportunity for expansion o~ the gas in the expansion chambers o~ a labyrinth seal.
Further, most o~ the prior art e~ort have ~ocused on reducing leakage across the stripper between the inlet and outlet ends o~ the chamber while ignoring the ~act that leakage likewise may occur between points in the chamber which are not necessarily closely adjacent the inlet or outlet.
The present invention is directed to a solution o~
the problems discussed above.
SUMMARY OF THE lNv~NllON
In accordance with the present invention, leakage through the gap between the opposed side sur~aces o~ the pump housing and impeller is minimized by forming a ~plurality o~ concentrically arranged series o~ pockets in one o~ the opposed side sur~aces. Each series o~ pockets includes a plurality o~ pockets circum~erentially spaced -~1~9~
~rom each other in a circular array about the impeller axis. The pockets o~ each series are so located that the pockets of one series circum~erentially overlap the space between the pockets o~ the adjacent series. This arrangement assures that there is no truly direct line path o~ flow through the gap between separated locations in the pump chamber which open into the gap. Stated another way, any direct path through the gap between two points opening into the pump chamber is interrupted by at least one or more pockets so that the likelihood of establishing a continuous ~low path ~or leakage between the two points is minimal. This arrangement is the most e~ective when the pockets are formed in the side sur~aces of the impeller in that ~luid which enters a pocket enters a moving pocket which disrupts the normal path o~ ~low.
Minimization o~ noise generated by the pump operation is accomplished by e~ectively doubling the number o~
vanes on the impeller and operating the impeller at rotative speeds such that noise which is generated is generated at ~reguencies above the audible range. The rotor o~ the present invention is ~ormed with an annular web at its outer peripheral portion which lies in a general plane normal to the axis o~ rotation o~ the impeller. Vanes project radially outwardly ~rom opposite sides of the web and are variably spaced ~rom each other in a calculated mirror image pattern which is duplicated, but angularly o~set by 180~ at opposite sides o~ the impeller. The vane spacing and arrangement is such that no vane on one side o~ the rotor is in axial alignment with a vane on the opposite side o~ the rotor.
E~ectively, this doubles the total number o~ vanes and the axial extent o~ the individual vanes is reduced so that the ~low discontinuity created by the passage o~ a vane across a stripper edge is minimized By choosing the number o~ vanes to be located at one side o~ the impeller web to be the largest odd number o~ vanes consistent with convenient ~abrication o~ the rotor (tooling or mold structure may establish a minimum limit to the spacing between adjacent vanes) and selecting a calculated vane spacing sequence a geometrically balanced impeller with variable vane spacing can be achieved.
As embodied and broadly described herein, the invention provides a toric pump comprising an impeller housing having a ~ront end ~ace lying in a ~irst general plane and a cup shaped impeller receiving recess in said ~ront end ~ace having a bottom sur~ace lying in a second general plane parallel to said ~irst general plane, said recess having a central axis normal to said ~irst and second general planes, an impeller received in said impeller receiving recess ~or rotation about said axis, said impeller having front and rear side sur~aces lying in parallel general planes normal to said axis and disposed between and respectively closely adjacent to said ~irst and second general planes, an impeller cover having a ~ront face and a flat rear face disposed in sealed face to ~ace engagement with said front end face o~ said housing around the periphery o~ said impeller receiving recess, means de~ining a pump chamber in said rear ~ace of said impeller cover cooperable with said impeller and extending circumferentially of said axis from an inlet end to an outlet end circum~erentially separated ~rom said inlet end by a stripper portion o~ said rear face, said impeller cover having externally accessible outlet port means in ~luid communication with said outlet end o~ said pump chamber, means de~ining a generally cup shaped filter receiving recess in said ~ront ~ace of said cover having an inlet passage opening from said filter receiving recess into said pump chamber at said inlet end, a ~ilter cover mounted on said ~ront ~ace o~ said impeller cover in overlying relation to said filter receiving recess and sealingly engaged with said front ~ace around the periphery o~ said ~ilter receiving recess, means de~ining an externally accessible inlet port in said ~ilter cover opening into said filter receiving recess at a location remote ~rom said inlet end in said impeller cover, and filter means resiliently gripped between said ~ilter cover and said impeller cover between said inlet port and said inlet passage.
Other objects and ~eatures of the invention will become apparent by reference to the ~ollowing speci~ication and to the drawings.

~ 9~5~

IN THE DRAWINGS
Fig. 1 is a front view of a regeneration toric pump embodying the present invention;
Fig. 2 is a rear view showing the inner slde of the pump housing cover of the pump of Fig. 1;
Fig. 3 is a ~ront view showing the interior side of the pump housing of the pump of Fig. 1;
Fig. 4 is a cross sectional view taken on line 4-4 of Fig. 1;
Fig. 5 is a detailed cross sectional view taken on line 5-5 o~ Fig. 1;
Fig. 6 is a side view of the impeller employed in the pump of Fig. 1, showing the front side of the impeller;
Fig. 7 is a detailed cross sectional view o~ the impeller taken on line 7-7 of Fig. 6;
Fig. 7A is an edge view o~ the impeller showing a portion o~ the outer periphery o~ the impeller;
Fig. 8A is a schematic diagram illustrating the pattern o~ vane spacing employed at the front side o~ the impeller; and Fig. 8B is a schematic diagram illustrating the pattern o~ vane spacing employed on the rear side o~ the impeller.
Re~erring ~irst to Figs. 1-5, a regenerative toric pump embodying the present invention includes an impeller housing designated generally 20 and a housing cover designated generally 22 ~ixedly and sealingly secured to ~ 3 each other as by bolts 24. For purposes of orientation, that side of the pump on which the cover 22 is located will be referred to as the front of the pump. Housing 20 is formed with a forwardly opening impeller receiving recess having a flat bottom surface 26 and an annular recess 28 which, as best seen in Fig. 3, extends circumferentially of the housing about a central housing axis A from an inlet end 30 to an outlet end 32 which are separated from each other by a stripper section 34 coplanar with the surface 26.
Cover 22 is formed with a flat rear face 36 and a similar annular recess 38 which extends circumferentially from an inlet 40 opening from recess 38 forwardly through the cover to an outlet 42 which likewise opens forwardly through cover 20, the inlet and outlet ends of the annular recess 38 being separated from each other by a stripper portion 44 coplanar with the flat rear face 36 of cover 20.
As best seen in Figs. 4 and 5, when cover 22 is assembled upon housing 20, the flat faces 26 and 36 of the housing and cover respectively are disposed in spaced parallel relationship to each other by a distance which slightly exceeds the axial thickness of a disk shaped impeller designated generally 46 (see Figs. 6 and 7) indicated in broken line only in Figs. 4 and 5. Impeller 46 iS received within the pump housing for rotation about the axis A and is rotatively fixed upon the end of an :

~ ~3~
impeller drive shaft 48 rotatably mounted within a bore 50 coaxial with axis A of housing 20 as by a bearing 52.
Impeller vanes 58, 60 respectively formed on the front and rear sides of the impeller are operable upon rotation of 5 the impeller to impel air along the respective annular recesses of pump chambers 38, 28 in a well known manner.
The clearance between the opposite side surfaces o~
impeller 46 and the flat sur~aces 26, 36 on the housing and cover is chosen to be sufficient so as to assure there will be no contact between the rotating impeller and the fixed surfaces 26, 36 during operation of the pump. For reasons to be explained in more detail below, it is desirable that the impeller be driven at relatively high speeds of rotation - in the order of 10,000 rpm or higher - and any contact between the impeller and housing surfaces during operation must be avoided.
Similarly, a relatively small gap or clearance between the outer peripheral surface 54 of the impeller and the opposed peripheral surface 34C, (Figs. 3 and 5) of the stripper portion of the impeller receiving recess in housing 20 is required. Because recess 28 in housing 22 is located at the rear side o~ the impeller, and the inlet 40 and outlet 42 of the pump enter the interior chamber through the cover at the front side of impeller 46, recesses 28 and 38 are ~ormed at their inlet ends 30, 40 with radially outwardly extending enlarged portions 3 OA, 40A so that fluid entering through inlet 40A can flow across the outer periphery 54 o~ impeller 46 via the enlargements 40A, 30A to the rear side o~ the impeller.
Similar enlarged portions 32A, 42A are ~ormed at the outlet ends 32, 42 o~ the recesses 28, 38.
In the particular cover 22 shown in the drawings, external connections to inlet and outlet 42 are made through a ~ilter housing indicated in broken line at F in Figs. 4 and 5 which is seated upon a ~ilter chamber de~ining ~ormation designated generally 60 on the ~ront side o~ cover 22. The ~ilter F - ~ilter chamber 62 arrangement provides a convenient means ~or ~iltering incoming air when the pump is employed to pump air. While the pump disclosed in the application drawings is speci~ically intended to supply air as required to an automotive emission control system, the pump described has other applications and is readily adapted ~or use in pumping liquid or ~luids other than air.
Regenerative toric pumps of the general type here disclosed are known in the prior art and, as stated above, have two inherent problems in their design. The ~irst o~
these two problems is the generation o~ noise resulting ~rom the cyclic passage o~ the rotor vanes into and out o~
the restricted passage constituted by the opposed stripper portions 34, 44 whose presence is required to de~lect fluid ~rom the annular recess or pump chamber into the pump outlet. The second problem is that o~ leakage o~ the ~luid being pumped through the clearance gaps between the opposed sur~aces o~ the rotating impeller and pump housing.
The present invention addresses the problem o~ noise generation by employing a relatively large number o~ vanes on the impeller which are arranged in a predetermined non uni~ormly spaced pattern and by ~orming the stripper portion edges to extend along a non-radially inclined edge.

Re~erring now particularly to Fig. 3, it is seen that the edges 34A, 34B of the stripper portion 34 o~ the pump housing do not lie on lines radial to axis A, such as lines R1 and R2, but are instead inclined to those radial lines. As will be described in more detail below, the various vanes 58, 60 of the impeller lie in general planes which extend radially ~rom axis A. In Fig. 3, which shows the ~ront side o~ housing 20, the direction o~ rotation o~
the impeller would be in a counter-clockwise direction so that the vanes would advance air (or whatever ~luid is being pumped) along the annular recess 28 ~rom inlet end 30 to outlet end 32. Because o~ the inclination o~ edge 34B o~ the stripper to the radial line R2, as a vane on the impeller passes in a counterclockwise direction ~rom outlet end 32 o~ recess 28 into overlying relationship with the stripper portion 34, the radially extending vane is inclined to the stripper edge 34B so that as the vane advances ~rom the relatively large passage de~ined by the ~ 21~9~

annular recess 28 into the relatively restricted passage defined by stripper portion 34, the entire vane does not attempt to enter this restricted passage simultaneously, as would be the case i~ both the vane and edge 34B
extended in a radial direction. E~ectively, the inclination o~ edge 34B to the radial line R2 slices air ~rom the vane edge, rather than chopping it as would be the case i~ edge 34B extended along a radius ~rom axis A.
This arrangement cushions to some extent the ~luid shock occasioned by the transit o~ the vane ~rom a relatively unrestricted passage into an extremely restricted passage.
A similar action occurs at edge 34A, and as is best seen in=Fig. 2, the corresponding edges 44A and 44B o~ the opposed stripper portion 44 on cover 22 are inclined similarly to radial lines extending ~rom the axis A.
Typically, the impeller 46 will be driven in rotation at a substantially constant speed which, i~ the vanes are equally spaced about the impeller circum~erence, will result in the passage o~ a vane edge across the edge o~
the stripper at a substantially constant cyclic ~requency.
Noise generated will be o~ this ~requency and its harmonics and, whe-n one o~ these ~requencies approaches some natural ~requency of the pump structure, ampli~ication o~ the noise can occur. The prior art has recognized that some noise generation is inherent where an impeller with equally spaced vanes is driven at a constant speed across a stripper, and that noise generation may be s~a reduced by arranging the vanes in a pattern in which the vanes are unequally spaced to avoid a constant frequency generation situation. However, unequal spacing o~ the impeller vanes typically creates other problems, such as impeller imbalance and increased manu~acturing costs.
A second approach to minimizing the noise generation problem is to generate noise at ~requencies above the audible range which, ~or most persons means ~requencies above 15,000 cycles per second. In that the ~requency of noise generated by the pump is essentially the product of the number o~ vanes on the impeller multiplied by the number o~ impeller revolutions per second, high speed operation o~ an impeller with a relatively large number o~
vanes o~ers the possibility o~ avoiding the generation o~
noise within the audible range.
Both o~ these approaches are employed in the impeller of the present invention, with special care being given to determining a pattern o~ variable vane spacing which also results in a geometric balance o~ the impeller.
Re~erring ~irst to the cross sectional view o~ Fig.
7, impeller 46 is ~ormed with an annular web 66 at its outer peripheral portion which lies in a general plane normal to the impeller axis mid-way between the ~ront and rear side sur~aces o~ the impeller. Vanes 58 project ~orwardly ~rom the ~ront side of web 66 and vanes 60 project rearwardly ~rom the rearward side o~ web 66.
Re~erring now particularly to Fig. 6, which is a ~ront -~ ~a~~
view of the impeller, it is seen that the vanes 58 lie in general planes which contain the axis of impeller 46 and radiate from the axis in angularly spaced relationship to each other. As best seen in Fig. 7, the front edges 72 of the vanes 58 lie in the plane of the ~ront surface 68 o~
the impeller and the radially outer edges 74 of vane 58 extend flush with the outer periphery of web 66. Pockets 76 are formed between adjacent vanes 58. The vanes 60 which project from the rearward ~ace of web 66 are of a con~iguration similar to vanes 58.
In Fig. 6, the vanes on the front face o~ the rotor are aYranged in a pattern which is determined in the ~ollowing manner.
Rather than computing the space between adjacent vanes, which have a finite thickness, it is somewhat simpler and more convenient to assume that the vanes are of zero thickness and to compute the locations of the radial general planes which will bisect the space between adjacent vanes.
The first step in the procedure is to select a total number of spaces between the vanes at the front side of impeller 46. In order to assure that no vane on the front side of the impeller will be directly aligned with a vane on the rear side of the impeller, the number of spaces selected must be an odd number. The number chosen should be as large as possible, taking into account limitations ~ C~1~9~

imposed by structural strength requirements and the tooling and techniques employed to ~abricate the impeller.
The number o~ spaces selected is then divided into 360~ to determine the size (angular extent about the axis) o~ an average size space. To ~ollow an exemplary calculation, it will arbitrarily be assumed that 45 spaces are to be employed, in that this results in an average space o~ 360~ - 45 or 8~.
The next step is to determine a maximum increment to be added or subtracted from an average ~pace to determine the minimum and maximum space sizes. It will arbitrarily be assumed that the maximum departure ~rom the average space size o~ 8~ will be + 15~ o~ 8~ or 1.2~. This will give a maximum space size o~ 9.2~ and a minimum space size o~ 6.8~. The minimum space size should then be checked to be sure it can be achieved by the tooling and techniques employed in ~abricating the vanes. Typically, the impeller is ~ormed by an injection molding or die casting technique and the machining o~the mold or die cavity will be the determining ~actor.
With an odd number of spaces, the pattern o~ the vanes on the front face o~ impeller 46 will be established with respect to a re~erence line L (Fig. 8A) which extends diametrically o~ the impeller and passes through the impeller axis. With an odd number o~ spaces, the line L, as indicated in Fig. 8A, can be so located as to pass through the central general plane o~ one vane 58A and bisect the space between the two vanes 58B and 58C at theopposite side of the impeller circumference.
The next step is to locate, through one 180~
clockwise displacement ~rom the reference vane 58A
location the angular displacement from lien L of the radial lines L1, L2, etc., which bisect the successive spaces in a clockwise direction from line L1 through 180~, assuming all spaces are of the average size. Since the average size of the spaces is 8~, line L1 of Fig. 8A will be displaced an angle al from line L of 4~, line L2 will be displaced from line L1 by an angle a2 12~, subsequent lines L3, L4, etc., (not shown) will be displaced from the preceding line by 8~ increments. The angles al, a2 will be used in calculating the individual spacings.
For reasons which will become apparent, it is desired that the spaces in the first 90~ of displacement clockwise ~rom line L will be approximately, but not precisely symmetrically disposed with respect to the respective spaces in that quadrant between a 90~ displacement from line L and a 180~ displacement from line L. Therefore, it is convenient if the variation in space sizing follows some periodic function which will result in an increase in the space sizing through the ~irst 90~ ~rom line L and a decrease in space sizing through the next 90~. One obvious choice of such a function is a sine or cosine function.

-The sizes o~ the respective spaces clockwise ~rom re~erence vane 58A through the ~irst 180~ as viewed in Fig. 6 may be determlned by the following relationship:
S = D sin[2 x (an - 45~)] + B
where n = a number o~ the space counting clockwise ~rom re~erence vane 58A, S = the angular extent o~ the "space"
- i.e., the angular displacement between the general planes of two adjacent vanes, an = the angle between line L1 and the center line o~ space Sn i~ all spaces were o~
the average size - i.e., an = n x B - B, where B is the average space (8~ in the example given above) and D = the maximum increment to be added to or subtracted ~rom the average space size - D = 1.2~ in the example given above.
The above ~ormulation is but one o~ many which can be employed ~or computing a variable spacing between adjacent vanes. The foregoing ~ormulation establishes a vane spacing pattern in which the vanes spaces are o~ a minimum size adjacent re~erence vane 58A, increase progressively through the ~irst 90~ from line L1 and then decrease progressively to vane 58c.
The ~oregoing explanation has been concerned solely with determining the spacing o~ the vanes over the ~irst 180~ clockwise ~rom re~erence vane 58a. The spacing o~
the vanes at the opposite side o~ the line L which bisects re~erences vane 58a and the space between vanes 58B and 58C is precisely the same pattern except the spacing ~ 2139~0 progression commences at vane 58A and proceeds counter-clockwise as viewed in Figs. 6 and 8A through 180~ from vane 58A. In other words, the pattern of vanes 58 to the right of llne L of Fig. 8A is a precise mirror image of the vane spacing at the opposite side of line L. As viewed from the front, as in Fig. 6, the vane spacing or the pattern in which the vanes 58 are arranged about the impeller axis is geometrically balanced on opposite sides of a vertical line passing through the impeller axis as viewed in Fig. 6. To compensate for any imbalance on opposite sides of a horizontal line passing through the impeller axis, as might arise in the manu~acturing of the impeller, the vanes 60 at the rear side of impeller 46 are arranged in precisely the same pattern as the vanes 58 on the front side with the overall pattern displaced 180~
about the impeller axis. Thus, the vanes at the rear face of the impeller include a reference vane 60A from which the vane spacing progressively increases and decreases in the same amounts as that o~ the vanes 58 with the reference vane 60a being located at the six o'clock position as viewed in Fig. 8B as compared to the 12 o~clock position of the reference vane 58A on the front side of the impeller.
This arrangement achieves two important results.
First it achieves a geometric balance of the impeller as a whole on opposite sides of both a vertical and a horizontal plane passing through the impeller axis, and -second, as viewed in Fig. 7A, it assures that none o:E the vanes 58 at the front side oi~ the impeller wlll be axially aligned with any o~ the vanes 60 at the rear side o~ the impeller. E~f~ectively, as ~ar as the generation o:E noise is concerned, this latter arrangement presents twice as many vanes as would be the case i~ vanes 58 and 60 were axially aligned because with the disclosed arrangement, when a vane 58 at the front side o:E the impeller is passing across an edge o~ the stripper portion, there is no vane 60 aligned with the edge oi~ the stripper portion.
In the case o:E a 31~ inch diameter impeller with 59 vanes on each side, as shown in the drawings, the ~requency at which a vane edge - either an edge oE a :Eront vane 58 or a rear vane 60 - will pass an edge =oi~ the stripper portion will exceed 15,000 cycles per second if~
the speed oi~ rotation o:E the impeller exceeds approximately 8400 rpm. Suitable motors ~or driving an impeller of a 31~ inch diameter at speeds o:E up to 20,000 rpm in an air pumping application are readily available from a number o~ commercial sources.
The problem o:E leakage through the clearance gap between the opposed side sur~aces o~ the impeller and pump housing is usually believed to involve ~low across the stripper portions 34, 44 o~ the pump in that the highest pressure dii~erential within the pump exist between that side o~ the stripper ~acing the outlet and that side o~
the stripper i~acing the inlet. Most o~ the prior art -2 ~

efforts directed to reduction of gap leakage losses are concerned with leakage across the stripper, but overlook the fact that significant leakage can occur across the main housing surfaces 26 and 36 as, ~or example, across the surface 3 6 between points P1 and P2 (Fig. 2 ) . While the distances leakage o~ this latter type must traverse are much greater normally than across the stripper, and the pressure differential is much lower than the pressure differential across the stripper, the circum~erential extent of the gap through which= leakage may pass is substantially greater.
In accordance with the present invention, the opposed side sur~aces of the impeller radially inwardly of the impeller vanes are ~ormed with concentric series o~
recesses or pockets such as 80, 82, 84. These pockets 80, 82 and 84 provide expansion chambers into which fluid ~lowing through the gap between the impeller side sur~aces and housing side sur~aces can ~low. As compared to leakage ~low across opposed ~lat or unrecessed sur~aces, :~luid :Elowing into the recessed pockets 80, 82 and 84, is carried along with the pocket by rotation o~ the impeller and, at a high speed of rotation of the impeller will eventually be discharged ~rom the pocket at some random location and in a direction which normally will have some radially outwardly directed component o:E movement as well as a component o~ movement directed in general toward a high pressure region of the pump chamber. E~ectively, ~ 2 ~ 5 ~

this arrangement prevents the formation o~ any organized continuous ~low path through the gap.
One pre~erential arrangement of the pockets 80, 82, 84 is that shown in Fig. 6 in which the pockets extend in concentric circular patterns in uni~ormly circum~e-rentially spaced relationship within the circular pattern.
The circum~erential length and location o~ the pockets angularly about the impeller axis varies ~or each concentric circular array o~ pockets with the pockets 82 circum~erentially overlapping the space between adjacent pockets 80 o~ the next inner most ring, and with the pockets 84 o~ the outer most ring similarly circum~erentially overlapping the spaces between adjacent pockets 82 o~ the next inner most ring. This arrangement e~ectively positions one or more pockets in any direct path o~ ~low across the ~aces 26 or 36 o~ the housing which might extend between any two poin~s in the pump chamber such as P1 and P2 o~ Fig. 2 which are su~iciently spaced from each other to develop any substantial pressure dif~erential.
The con~iguration and location o~ the pockets 80, 82 and 84 may take any o~ several alternative ~orms which may be chosen in accordance with the structural requirements o~ the impeller and the tooling and ~abrication techniques employed to ~orm the pockets. Generally speaking, it is desired that a plurality o~ concentric rings o~ pockets in which the pockets in the respective rings circum~e-2~-~96~
rentially overlap the spaces between the pockets in adjacent rings be employed, and the arrangement shown in the drawings is but one example o~ such a preferred arrangement.
While it is greatly pre~erred that the pockets be ~ormed in the impeller, where the construction of the impeller makes this impractical, the pockets may be ~ormed in the housing and cover in the sur~aces 26, 36.
While examplary embodiments of the invention have been described above in detail, it will be apparent to those skilled in the art the disclosed embodiments may be modi~ied. Therefore, the ~oregoing description is to be considered exemplary rather than limiting, and the true scope o~ the invention is that de~ined in the ~ollowing claims.
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Claims (8)

1. A toric pump comprising an impeller housing having a front end face lying in a first general plane and a cup shaped impeller receiving recess in said front end face having a bottom surface lying in a second general plane parallel to said first general plane, said recess having a central axis normal to said first and second general planes, an impeller received in said impeller receiving recess for rotation about said axis, said impeller having front and rear side surfaces lying in parallel general planes normal to said axis and disposed between and respectively closely adjacent to said first and second general planes, an impeller cover having a front face and a flat rear face disposed in sealed face to face engagement with said front end face of said housing around the periphery of said impeller receiving recess, means defining a pump chamber in said rear face of said impeller cover cooperable with said impeller and extending circumferentially of said axis from an inlet end to an outlet end circumferentially separated from said inlet end by a stripper portion of said rear face, said impeller cover having externally accessible outlet port means in fluid communication with said outlet end of said pump chamber, means defining a generally cup shaped filter receiving recess in said front face of said cover having an inlet passage opening from said filter receiving recess into said pump chamber at said inlet end, a filter cover mounted on said front face of said impeller cover in overlying relation to said filter receiving recess and sealingly engaged with said front face around the periphery of said filter receiving recess, means defining an externally accessible inlet port in said filter cover opening into said filter receiving recess at a location remote from said inlet end in said impeller cover, and filter means resiliently gripped between said filter cover and said impeller cover between said inlet port and said inlet passage.

2. The invention defined in claim 1, wherein said housing includes a rear wall defining said bottom surface of said impeller receiving recess, drive motor means mounted on said rear wall at a rearward side thereof and having a rotatable drive shaft projecting through said rear wall coaxially of said axis, and means fixedly mounting said impeller upon a forward end of said drive shaft.

3. The invention defined in claim 1 wherein said impeller housing is of metal, and said impeller cover is of a molded thermoplastic material.

4. The invention defined in claim 1 wherein said impeller cover includes a first central post integrally formed on said impeller cover extending coaxially of said axis within said filter receiving recess to an end surface lying substantially in said first general plane, a first web lying in a first general radial plane containing said axis integral with and projecting radially outwardly from said first post to the side wall of said filter receiving recess at a location between said inlet passage in said impeller cover and said inlet port in said filter cover, said filter means comprising a block of resilient filter media having a central bore therethrough adapted to receive said first post and a slit extending radially outwardly from said bore adapted to receive said web.

5. The invention defined in claim 4 wherein said filter receiving recess is defined in part by a first side wall portion lying at a constant radial distance from said axis and extending circumferentially about said axis over an arc of approximately 180°, said inlet passage being located beyond one end of said first side wall portion and said inlet port in said filter cover being located beyond the other end of said first side wall portion, said block of filter media having a cylindrical side wall portion resiliently engaged with said first side wall portion of said filter receiving recess, said inlet port opening into said filter receiving recess between said web and said other end of said first side wall portion.

6. The invention defined in claim 1 wherein said filter cover has a rearwardly opening cup shaped filter receiving recess adapted to mate with and constitute an axially forward extension of said filter receiving recess in said impeller cover when said filter cover is mounted on said impeller cover, a second central post integral with said filter cover extending coaxially of said axis within said filter receiving recess in said filter cover to abut said end surface of said first central post of said impeller cover, and a second web lying in a second general radial plane integral with and projecting radially outwardly from said second post to the side wall of the filter receiving recess in said filter cover, said first and second webs having radially extending edges in substantial engagement with each other when said filter cover is mounted on said impeller cover to cooperatively define a barrier extending radially across the filter receiving recess between said inlet port in said filter cover and said inlet end in said impeller housing.

7. The invention defined in claim 6 wherein said filter means comprises a block of resilient filter media of an axial length greater than that of an extended filter receiving recess defined by the mating filter receiving recesses in said impeller and filter covers, said block of media having a central bore receiving the central posts of said impeller cover and filter cover and a slit extending the entire axial length of said block and radially outwardly from said bore receiving said first and second webs of said impeller and filter covers, said block being sealingly engaged with the side wall of said extended filter receiving recess at a location at an opposite side of said inlet port from the engaged first and second webs.

8. The invention defined in claim 7 wherein said block of filter media is formed with a plurality of spaced axially extending openings therethrough.