EP0608444A1 - Pompe à canal latéral - Google Patents

Pompe à canal latéral Download PDF

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Publication number
EP0608444A1
EP0608444A1 EP93101025A EP93101025A EP0608444A1 EP 0608444 A1 EP0608444 A1 EP 0608444A1 EP 93101025 A EP93101025 A EP 93101025A EP 93101025 A EP93101025 A EP 93101025A EP 0608444 A1 EP0608444 A1 EP 0608444A1
Authority
EP
European Patent Office
Prior art keywords
impeller
pockets
vanes
side wall
wall surfaces
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP93101025A
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German (de)
English (en)
Inventor
John E. Smith
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Coltec Industries Inc
Original Assignee
Coltec Industries Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Coltec Industries Inc filed Critical Coltec Industries Inc
Priority to EP93101025A priority Critical patent/EP0608444A1/fr
Publication of EP0608444A1 publication Critical patent/EP0608444A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D23/00—Other rotary non-positive-displacement pumps
    • F04D23/008—Regenerative pumps
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D29/00—Details, component parts, or accessories
    • F04D29/18—Rotors
    • F04D29/188—Rotors specially for regenerative pumps
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D29/00—Details, component parts, or accessories
    • F04D29/66—Combating cavitation, whirls, noise, vibration or the like; Balancing
    • F04D29/669—Combating cavitation, whirls, noise, vibration or the like; Balancing especially adapted for liquid pumps
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D5/00—Pumps with circumferential or transverse flow
    • F04D5/002—Regenerative pumps

Definitions

  • 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 of 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 side surfaces and a peripheral surface which closely enclose the impeller but allow sufficient clearance such that the fluid can exit the impeller radially and then turn forward 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 of the passage a relatively narrow portion of 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 functions to deflect fluid being impelled through the pump chamber by the impeller vanes into the pump outlet instead of being pumped back to the inlet.
  • variable vane spacing usually results in the creation of at least some rotor imbalance which in turn leads to problems potentially more serious than undesirable noise.
  • a second problem encountered by pumps of types described above results from the fact that a slight clearance or gap must exist between the stationary pump housing surfaces and the adjacent rotating surfaces of the impeller in order that the impeller can freely rotate relative to the housing.
  • Those portions of the chamber side surfaces and the opposed side surfaces of the impeller which are located radially inwardly of the toroidal pump chamber present a gap which extends the entire length of the radially inner side of the circumferentially extending pump chamber. Pressure progressively increases in this chamber from the inlet end to the outlet end, and the clearance gap provides a path for leakage of fluid from high pressure regions of the chamber to regions of lower pressure.
  • the fluid being pumped is of low viscosity - i.e., air for example - this leakage can be substantial and substantially reduce the flow delivered by the pump.
  • Labyrinth seals rely upon a series of restrictions separated by expansion chambers which are intended to enable the fluid entering the chamber to expand to an increased volume or bulk which is in theory more difficult to pass through the next following restriction.
  • the fluid is of low compressibility, such as a liquid
  • no expansion takes place and the presence of the expansion chambers reduces the area available for restriction, thus reducing the effectiveness of the seal.
  • the pump of the type described above is employed to pump gasses, the gasses are highly compressible, but the pumps typically develop only a relatively small pressure differential between the inlet and outlet.
  • the present invention is directed to a solution of the problems discussed above.
  • leakage through the gap between the opposed side surfaces of the pump housing and impeller is minimized by forming a plurality of concentrically arranged series of pockets in at least one of the opposed side surfaces.
  • Each series of pockets includes a plurality of pockets circumferentially spaced from each other in a circular array about the impeller axis.
  • the pockets of each series are so located that the pockets of one series circumferentially overlap the space between the pockets of the adjacent series.
  • 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 flow path for leakage between the two points is minimal.
  • This arrangement is the most effective when the pockets are formed in the side surfaces of the impeller in that fluid which enters a pocket enters a moving pocket which disrupts the normal path of flow.
  • the rotor of the present invention is formed with an annular web at it outer peripheral portion which lies in a general plane normal to the axis of rotation of the impeller. Vanes project radially outwardly from opposite sides of the web and are variably spaced from each other in a calculated mirror image pattern which is duplicated, but angularly offset by 180° at opposite sides of the impeller.
  • the vane spacing and arrangement is such that no vane on one side of the rotor is in axial alignment with a vane on the opposite side of the rotor.
  • this doubles the total number of vanes and the axial extent of the individual vanes is reduced so that the flow discontinuity created by the passage of a vane across a stripper edge is minimized.
  • a regenerative toric pump embodying the present invention includes an impeller housing designated generally 20 and a housing cover designated generally 22 fixedly and sealingly secured to each other as by bolts 24.
  • 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 22, 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 22.
  • Impeller 46 is received within the pump housing for rotation about the axis A and is rotatively fixed upon the end of an 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 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 of impeller 46 and the flat surfaces 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.
  • recesses 28 and 38 are formed at their inlet ends 30, 40 with radially outwardly extending enlarged portions 30A, 40A so that fluid entering through inlet 40 can flow across the outer periphery 54 of impeller 46 via the enlargements 40A, 30A to the rear side of the impeller.
  • Similar enlarged portions 32A, 42A are formed at the outlet ends 32, 42 of the recesses 28, 38.
  • 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 first of these two problems is the generation of noise resulting from the cyclic passage of the rotor vanes into and out of the restricted passage constituted by the opposed stripper portions 34, 44 whose presence is required to deflect fluid from the annular recess or pump chamber into the pump outlet.
  • the second problem is that of leakage of the fluid being pumped through the clearance gaps between the opposed surfaces of the rotating impeller and pump housing.
  • the present invention addresses the problem of noise generation by employing a relatively large number of vanes on the impeller which are arranged in a predetermined non uniformly spaced pattern and by forming the stripper portion edges to extend along a non radially inclined edge.
  • the edges 34A, 34B of the stripper portion 34 of 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.
  • the various vanes 58, 60 of the impeller lie in general planes which extend radially from axis A.
  • Fig. 3 which shows the front side of housing 20, the direction of rotation of the impeller would be in a counterclockwise direction so that the vanes would advance air (or whatever fluid is being pumped) along the annular recess 28 from inlet end 30 to outlet end 32.
  • edge 34B of the stripper Because of the inclination of edge 34B of the stripper to the radial line R2, as a vane on the impeller passes in a counterclockwise direction from outlet end 32 of 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 from the relatively large passage defined by the 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 if both the vane and edge 34B extended in a radial direction.
  • edge 34B slices air from the vane edge, rather than chopping it as would be the case if edge 34B extended along a radius from axis A.
  • This arrangement cushions to some extent the fluid shock occasioned by the transit of the vane from 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 of the opposed stripper portion 44 on cover 22 are inclined similarly to radial lines extending from the axis A.
  • the impeller 46 will be driven in rotation at a substantially constant speed which, if the vanes are equally spaced about the impeller circumference, will result in the passage of a vane edge across the edge of the stripper at a substantially constant cyclic frequency. Noise generated will be of this frequency and its harmonics and, when one of these frequencies approaches some natural frequency of the pump structure, amplification of 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 reduced by arranging the vanes in a pattern in which the vanes are unequally spaced to avoid a constant frequency generation situation.
  • unequal spacing of the impeller vanes typically creates other problems, such as impeller imbalance and increased manufacturing costs.
  • a second approach to minimizing the noise generation problem is to generate noise at frequencies above the audible range which, for most persons means frequencies above 15,000 cycles per second.
  • the frequency of noise generated by the pump is essentially the product of the number of vanes on the impeller multiplied by the number of impeller revolutions per second
  • high speed operation of an impeller with a relatively large number of vanes offers the possibility of avoiding the generation of noise within the audible range.
  • impeller 46 is formed 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 front and rear side surfaces of the impeller. Vanes 58 project forwardly from the front side of web 66 and vanes 60 project rearwardly from the rearward side of web 66.
  • Fig. 6 which is a front 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 front surface 68 of the impeller and the radially outer edges 74 of vanes 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 face of web 66 are of a configuration similar to vanes 58.
  • pockets 76 (see Fig. 7) defined by vanes 60, 58, as shown in Fig. 4, appear to have a lesser radial dimension than the corresponding radial dimension of pump chambers 38, 28. It should be recognized however that in practice, the radial extent of pockets 76 and chambers 38, 28 preferably should be as nearly equal as possible within the requirement for maintaining adequate clearance between the outer peripheral surface 54 of the impeller and the opposed peripheral inner suface 34C of the impeller receiving recess in housing 20.
  • vanes on the front face of the rotor are arranged in a pattern which is determined in the following manner.
  • vanes are of zero thickness and to compute the locations of the radial general planes which will bisect the space betwen 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.
  • the number of spaces selected must be an odd number. The number chosen should be as large as possible, taking into account limitations imposed by structural strength requirements and the tooling and techniques employed to fabricate the impeller.
  • the number of spaces selectes is then divided into 360° to determine the size (angular extent about the axis) of an average size space.
  • size angular extent about the axis
  • 45 spaces are to be employed, in that this results in an average space of 360° ⁇ 45 or 8°.
  • the next step is to determine a maximum increment to be added or substracted from an average space to determine the minimum and maximum space sizes. It will arbitrarily be assumed The next step is to determine a maximum increment to be added or subtracted from an average space to determine the minimum and maximum space sizes. It will arbitrarily be assumed that the maximum departure from the average space size of 8° will be ⁇ 15% of 8° or 1.2°. This will give a maximum space size of 9.2° and a minimum space size of 6.8°. The minimum space size should then be checked to be sure it can be achieved by the tooling and techniques employed in fabricating the vanes. Typically, the impeller is formed by an injection molding or die casting technique and the machining of the mold or die cavity will be the determining factor.
  • the pattern of the vanes on the front face of impeller 46 will be established with respect to a reference line L (Fig. 8A) which extends diametrically of the impeller and passes through the impeller axis.
  • the line L as indicated in Fig. 8A, can be so located as to pass through the central general plane of one vane 58A and bisect the space between the two vanes 58B and 58C at the opposite side of the impeller circumference.
  • the next step is to locate, through one 180° clockwise displacement from the reference vane 58A location the angular displacement from line 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 a1 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 a1, a2 will be used in calculating the individual spacings.
  • the spaces in the first 90° of displacement clockwise from 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 first 90° from line L and a decrease in space sizing through the next 90°.
  • a function is a sine or cosine function.
  • the above formulation is but one of many which can be employed for computing a variable spacing between adjacent vanes.
  • the foregoing formulation establishes a vane spacing pattern in which the vane spaces are of a minimum size adjacent reference vane 58A, increase progressively through the first 90° from line L1 and then decrease progressively to vane 58C.
  • 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.
  • 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.
  • 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 of 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 of the vanes 58 at the front side of the impeller will be axially aligned with any of the vanes 60 at the rear side of the impeller.
  • this latter arrangement presents twice as many vanes as would be the case if vanes 58 and 60 were axially aligned because with the disclosed arrangement, when a vane 58 at the front side of the impeller is passing across an edge of the stripper portion, there is no vane 60 aligned with the edge of the stripper portion.
  • the opposed side surfaces of the impeller radially inwardly of the impeller vanes are formed with concentric series of recesses or pockets such as 80, 82, 84.
  • These pockets 80, 82 and 84 provide expansion chambers into which fluid flowing through the gap between the impeller side surfaces and housing side surfaces can flow.
  • fluid flowing into the recessed pockets 80, 82 and 84 is carried along with the pocket by rotation of the impeller and, at a high speed of rotation of the impeller will eventually be discharged from the pocket at some random location and in a direction which normally will have some radially outwardly directed component of movement as well as a component of movement directed in general toward a high pressure region of the pump chamber. Effectively, this arrangement prevents the formation of any organized continuous flow path through the gap.
  • the pockets 80, 82 and 84 are elongated circumferentially of the impeller and each circular array of pockets has a uniform length proportional to the radial distance between the pockets and the impeller axis.
  • the circumferential length of the pockets 80, 82 and 84 in any circular array exceeds the space between the pockets in a next adjacent circular array. If an imaginary line were drawn on Fig. 6 extending radially from the impeller axis to bisect the space between two adjacent pockets of one circular array, the imaginary line would also circumferentially bisect a pocket in an adjacent circular array.
  • the pocket arrangement disclosed provides further advantages from the manufacturing standpoint where the impeller is molded from a thermoplastic or lightweight metal such as aluminum.
  • the amount of gap leakage is essentially dependent upon the magnitude of the gap between the side faces of the impeller and the respective opposed housing side wall surfaces 26 and 36. If the side surfaces 68, 70 of the impeller were not formed with the pockets 80, 82, 84, uneven cooling of the impeller in the mold normally would result in an uneven - i.e., a non-flat side surface of the impeller.
  • the pattern of the pockets as viewed in Fig. 6 also facilitates an even radially outward flow of the molten plastic or metal which flows into the impeller forming mold at the center of the impeller.
  • One preferential arrangement of the pockets 80, 82, 84 is that shown in Fig. 6 in which the pockets extend in concentric circular patterns in uniformly circumferentially spaced relationship within the circular pattern.
  • the circumferential length and location of the pockets angularly about the impeller axis varies for each concentric circular array of pockets with the pockets 82 circumferentially overlapping the space between adjacent pockets 80 of the next inner most ring, and with the pockets 84 of the outer most ring similarly circumferentially overlapping the spaces between adjacent pockets 82 of the next inner most ring.
  • This arrangement effectively positions one or more pockets in any direct path of flow across the faces 26 or 36 of the housing which might extend between any two points in the pump chamber such as P1 and P2 of Fig. 2 which are sufficiently spaced from each other to develop any substantial pressure differential.
  • the configuration and location of the pockets 80, 82, and 84 may take any of several alternative forms which may be chosen in accordance with the structural requirements of the impeller and the tooling and fabrication techniques employed to form the pockets. Generally speaking, it is desired that a plurality of concentric rings of pockets in which the pockets in the respective rings circumferentially, symmetrically overlap the spaces between the pockets in adjacent rings be employed, and the arrangement shown in the drawings is but one example of such a preferred arrangement.
  • the pockets may advantageously be formed in the impeller as described above, where the construction of the impeller makes this impractical, or if desired by the manufacturer and/or end user, the pockets may be formed in the housing and cover in the surfaces 26, 36.
  • An alternate housing is designated generally as 120 and an alternate housing cover is designated as 122.
  • the opposed housing side wall surfaces 26, 36, radially inwardly of annular recesses 28, 38, respectively, are formed with concentric series of recesses or pockets such as 180, 182, 184, as best seen in Fig. 10.
  • the structure and advantages of pockets 180, 182 and 184 are as described above in relation to pockets 80, 82 and 84.
  • pockets 180, 182, 184 may be formed in either housing 120 or cover 122 or both, and that impeller 46 may be formed without any pockets whatsoever formed therein. Further, any combination is possible: the pockets may be formed in one side face of the impeller 46 and one side wall surface of the housing; pockets can be in both side faces of impeller 46 and one side wall surface of the housing, etc. As such, in the preferred embodiments, the pockets may advantageously be formed in neither, one or both of the side wall surfaces 26, 36 of the housing in addition to, or in lieu of the pockets formed in impeller 46.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Structures Of Non-Positive Displacement Pumps (AREA)
EP93101025A 1993-01-23 1993-01-23 Pompe à canal latéral Withdrawn EP0608444A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP93101025A EP0608444A1 (fr) 1993-01-23 1993-01-23 Pompe à canal latéral

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Application Number Priority Date Filing Date Title
EP93101025A EP0608444A1 (fr) 1993-01-23 1993-01-23 Pompe à canal latéral

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EP0608444A1 true EP0608444A1 (fr) 1994-08-03

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EP93101025A Withdrawn EP0608444A1 (fr) 1993-01-23 1993-01-23 Pompe à canal latéral

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001071193A1 (fr) * 2000-03-21 2001-09-27 Siemens Aktiengesellschaft Pompe de circulation
US9086071B2 (en) 2009-05-20 2015-07-21 Edwards Limited Side-channel pump with axial gas bearing

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT322718B (de) * 1971-12-18 1975-06-10 Rohs Ulrich Dipl Ing Seitenkanal verdichter
DE3811990A1 (de) * 1987-04-10 1988-10-20 Speck Pumpenfabrik Walter Spec Peripheralpumpe
US4872806A (en) * 1987-05-15 1989-10-10 Aisan Kogyo Kabushiki Kaisha Centrifugal pump of vortex-flow type
EP0450362A1 (fr) * 1990-03-28 1991-10-09 Coltec Industries Inc Pompe à canal latéral

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT322718B (de) * 1971-12-18 1975-06-10 Rohs Ulrich Dipl Ing Seitenkanal verdichter
DE3811990A1 (de) * 1987-04-10 1988-10-20 Speck Pumpenfabrik Walter Spec Peripheralpumpe
US4872806A (en) * 1987-05-15 1989-10-10 Aisan Kogyo Kabushiki Kaisha Centrifugal pump of vortex-flow type
EP0450362A1 (fr) * 1990-03-28 1991-10-09 Coltec Industries Inc Pompe à canal latéral

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001071193A1 (fr) * 2000-03-21 2001-09-27 Siemens Aktiengesellschaft Pompe de circulation
KR100760054B1 (ko) * 2000-03-21 2007-09-18 지멘스 악티엔게젤샤프트 급수 펌프
US9086071B2 (en) 2009-05-20 2015-07-21 Edwards Limited Side-channel pump with axial gas bearing
US9127685B2 (en) 2009-05-20 2015-09-08 Edwards Limited Regenerative vacuum pump with axial thrust balancing means
US9334873B2 (en) 2009-05-20 2016-05-10 Edwards Limited Side-channel compressor with symmetric rotor disc which pumps in parallel

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