CENTRIFUGAL PUMP ASSEMBLY

Abstract

A centrifugal pump assembly includes a pump head, a pump base defining a pump inlet and a pump outlet, a fluid outlet channel from the pump head to the pump outlet, impellers, defining an impeller fluid channel between an impeller inlet and outlet and connected with one of rotor shaft segments including a positive fit coupling for torque transfer between at least two rotor shaft segments, and one or more pump stage housing segments arranged between the pump base and the pump head. The pump stage housing segments have a structure defining a guide passage for receiving pumped fluid from the impeller outlet of the impellers and for guiding pumped fluid to the impeller inlet of another one of the impellers or to the pump head. The pump stage housing segments each have a structure defining at least a part of a wall section of the fluid outlet channel.

Claims

1. A centrifugal pump assembly comprising: a pump head configured to connect to or be integral with a motor stool and/or a motor housing; a pump base defining a pump inlet and a pump outlet; at least one fluid outlet channel configured to guide pumped fluid from the pump head to the pump outlet; at least two rotor shaft segments coaxially aligned and extending along a rotor axis, wherein each of the rotor shaft segments comprises a first axial end facing away from the pump head and a second axial end facing away from the pump base; one or more impellers, each of the impellers having a structure defining at least one impeller fluid channel extending from an impeller inlet to an impeller outlet, wherein each of the one or more impellers is fixed to or structurally integral with one of the rotor shaft segments, wherein the first axial end of one of the rotor shaft segments comprises a positive fit coupling configured for coupling with the second axial end of another one of the rotor shaft segments for torque transfer between the at least two rotor shaft segments; and one or more pump stage housing segments arranged between the pump base and the pump head, wherein each of the pump stage housing segments have a structure defining a guide passage for receiving pumped fluid from the impeller outlet of one of the one or more impellers and for guiding pumped fluid to the impeller inlet of another one of the one or more impellers or to the pump head, wherein the one or more pump stage housing segments each have a structure defining at least a part of a wall section of the at least one fluid outlet channel.

2. The centrifugal pump assembly according to claim 1, wherein at least one of the one or more impellers is received within the pump base, wherein said at least one of the one or more impellers is rotatably arranged within the pump base.

3. The centrifugal pump assembly according to claim 1, wherein each of the impellers and/or rotor shaft segments defines at least one rotating axial bearing surface facing towards the pump base arranged in sliding contact with a corresponding static axial bearing surface defined by one of the one or more pump stage housing segments or the pump base and facing towards the pump head.

4. The centrifugal pump assembly according to claim 1, wherein the positive fit coupling of the rotor shaft segments is axially loose.

5. The centrifugal pump assembly according to claim 1, wherein each of the impellers and/or the rotor shaft segments defines at least one rotating radial bearing surface facing radially outward and arranged in sliding contact with a corresponding static radial bearing surface that is defined by one of the pump stage housing segments or the pump base and facing radially inward.

6. The centrifugal pump assembly according to claim 1, wherein at least one of the group comprising: at least one of the one or more pump stage housing segments; at least one of the one or more impellers; the pump head; and the pump base has a single integral additively manufactured structure.

7. The centrifugal pump assembly according to claim 1, wherein the one or more pump stage housing segments each have a structure defining the wall section of the at least one fluid outlet channel, wherein the wall section fully circumferentially encloses fluid pumped through the at least one fluid outlet channel.

8. The centrifugal pump assembly according to claim 1, further comprising a fluid outlet channel sleeve circumferentially enclosing the one or more pump stage housing segments, wherein the one or more pump stage housing segments each have a structure defining a part of the wall section of the at least one fluid outlet channel, wherein the part of the wall section and the fluid outlet channel sleeve complement each other to define the at least one fluid outlet channel.

9. The centrifugal pump assembly according to claim 1, wherein the one or more pump stage housing segments each comprise a first mechanical coupling at a first axial segment end facing towards the pump base and a second mechanical coupling at a second axial segment end facing towards the pump head, wherein the one or more pump stage housing segments is coupled to the pump base or to another pump stage housing segment by the first mechanical coupling, and wherein the one or more pump stage housing segments is coupled to the pump head or to another pump stage housing segment by the second mechanical coupling.

10. The centrifugal pump assembly according to claim 9, wherein the first mechanical coupling is formed as a corresponding coupling counterpart to the second mechanical coupling for being releasably coupled to a second coupling of another pump stage housing segment.

11. The centrifugal pump assembly according to claim 9, wherein the first mechanical coupling and/or the second mechanical coupling of the one or more pump stage housing segments predefine one or more distinct rotational mounting positions of said one or more pump stage housing segments.

12. The centrifugal pump assembly according to claim 9, wherein the first mechanical coupling and the second mechanical coupling define corresponding coupling counterparts of a bayonet coupling.

13. The centrifugal pump assembly according to claim 8, further comprising at least one sealing element for sealing the at least one fluid outlet channel.

14. The centrifugal pump assembly according to claim 1, wherein the pump head defines a reverse channel for receiving pumped fluid from one of the one or more impellers and redirecting the pumped fluid to the at least one fluid outlet channel section of one of the pump stage housing segments that is coupled to the pump head.

15. The centrifugal pump assembly according to claim 14, wherein the pump head is connected to or is integral with the motor housing and the reverse channel extends through the motor housing in thermal contact with heat-generating components of the motor, so that the pumped fluid cools the heat-generating components of the motor.

16. The centrifugal pump assembly according to claim 1, wherein an axial buffer room is provided between the first axial end of the rotor shaft segment and the second axial end of another one of the rotor shaft segments that is positively coupled thereto for torque transfer between said coupled rotor shaft segments.

17. The centrifugal pump assembly according to claim 16, wherein the axial buffer room is at least partly filled by a buffer medium.

18. The centrifugal pump assembly according to claim 1, wherein the pump base defines a fluid suction inlet channel extending from the pump inlet to a suction eye, wherein the suction eye is arranged coaxial with the rotor axis and laterally surrounds a rotor shaft segment of one of the one or more impellers.

19. The centrifugal pump assembly according to claim 18, wherein the pump base defines a tubular element arranged coaxially within the suction eye for receiving the rotor shaft segment of said impeller, wherein the tubular element provides at least one static inner radial bearing surface in sliding contact with a rotating outer radial bearing surface of the rotor shaft segment of said impeller.

20. The centrifugal pump assembly according to claim 1, wherein the centrifugal pump is free of at least one of: a shaft extending from the pump head to the pump base; and tie rods or straps for holding the pump head and the pump base together.

21. The centrifugal pump assembly according to claim 1, wherein the impeller outlet faces away from the pump base and an inlet of the guide passage faces towards the pump base, wherein the inlet of the guide passage is arranged to receive pumped fluid from the impeller outlet.

22. The centrifugal pump assembly according to claim 1, wherein all of the one or more impellers are identical in shape, size and material.

23. The centrifugal pump assembly according to claim 1, wherein all of the one or more pump stage housing segments are identical in shape, size and material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Embodiments of the present disclosure will now be described by way of example with reference to the following figures of which:

[0044] FIG. 1 is an exploded perspective view of an embodiment of a centrifugal pump assembly according to the present disclosure;

[0045] FIGS. 2a and 2b are perspective views showing a mechanical coupling mechanism between pump stage housing segments of an embodiment of a centrifugal pump assembly according to the present disclosure;

[0046] FIG. 3 is a longitudinal sectional view of three rotor shaft segments in an embodiment of a centrifugal pump assembly according to the present disclosure;

[0047] FIGS. 4a and 4b are perspective views showing an impeller (including a rotor shaft segment) of an embodiment of a centrifugal pump assembly according to the present disclosure;

[0048] FIG. 5 is a partial longitudinal sectional view of a pump stage of an embodiment of a centrifugal pump assembly according to the present disclosure;

[0049] FIG. 6 is a longitudinal sectional view of a pump base of an embodiment of a centrifugal pump assembly according to the present disclosure;

[0050] FIG. 7 is a partial longitudinal sectional view of two pump stages of an alternative embodiment of a centrifugal pump assembly according to the present disclosure; and

[0051] FIG. 8 is a longitudinal sectional view of an embodiment of a centrifugal pump assembly according to the present disclosure.

DETAILED DESCRIPTION

[0052] FIG. 1 shows a centrifugal pump assembly 1 in form of a vertical multistage centrifugal pump assembly comprising a vertical rotor axis z and n=3 pump stages, i.e. three impellers 3a-c. The centrifugal pump assembly 1 comprises a pump base 5, three impellers 3a-c, two pump stage housing segments 7a,b, three sealing elements 9a-c and a pump head 11, i.e. in total ten separate parts (without counting parts of a motor and motor control electronics). The number of parts of the centrifugal pump assembly 1 shown in FIG. 1 is significantly reduced compared to a conventional multistage centrifugal pump assembly comprising three pump stages. Except for the sealing elements 9a-c, one, some or all of the other seven parts shown in FIG. 1 are preferably additively manufactured.

[0053] The pump base 5 is an integral additively manufactured structure, preferably of a metallic material. The pump base 5 defines a pump inlet 13 and a pump outlet 15. The pump inlet 13 and the pump outlet 15 are arranged coaxially facing into opposite horizontal directions, so that the centrifugal pump assembly 1 may be installed into a straight pipe section. The pump base 5 further defines a stand structure with feet 17 standing on a floor or ground. The feet 17 comprise openings 18 for fastening the pump base 5 to the ground by means of fasteners, e.g. screws. An upper portion of the pump base 5 defines a reception structure for receiving the first impeller 3a. Said upper portion of the pump base 5 partly functions as a pump housing. More details of the pump base 5 can be seen in FIG. 6.

[0054] The impellers 3a-c each have a structure defining several impeller fluid channels extending from an impeller inlet 19 to an impeller outlet 21. The impeller inlet 19 faces towards the pump base 5, i.e. downward (better visible in FIG. 4b). The impeller outlet 21 faces towards the pump head 11, i.e. upward. The impeller outlet 21 is positioned radially more outward than the impeller inlet 19. The impeller fluid channels within the impellers 3a-c are separated from each other by impeller vanes 23 (better visible in FIGS. 3 and 4a). Furthermore, the impellers 3a-c each form, as in integral structure, a rotor shaft segment 25a-c extending predominantly in axial direction towards the pump base 5, i.e. downward. The rotor shaft segment 25a of the first, i.e. bottommost, impeller 3a extends into a suction eye 51 of the pump base 5 (better visible in FIG. 6). The rotor shaft segments 25b,c of the other impellers 3b,c extend into the respective pump stage housing segments 7a,b positioned axially below the respective impeller 3b,c (better visible in FIG. 3).

[0055] A first pump stage housing segment 7a is arranged axially above the first impeller 3a, and a second pump stage housing segment 7b is arranged axially above the second impeller 3a. Both pump stage housing segments 7a,b are essentially identical in material and shape. As shown in more detail in FIG. 2a, they each comprise a first mechanical coupling 27 at a first axial segment end 29 facing towards the pump base 5 and a second mechanical coupling 31 at a second axial segment end 33 facing away from the pump base 5. The pump head 11 comprises an identical first mechanical coupling 27 at a (lower) pump head end 35 facing towards the pump base 5. Analogously, the pump base 5 comprises an identical second mechanical coupling 31 at an (upper) pump base end 37 facing towards the pump head 11. The first mechanical coupling 27 is a male component of a bayonet coupling in form of radially outward rivet-like protrusions. In the shown example, there are six radially outward rivet-like protrusions evenly distributed circumferentially. The second mechanical coupling 31 is a corresponding female component of a bayonet coupling in form of hook-shaped slots at a radial inner side for receiving a head of a rivet-like protrusion of the first mechanical coupling 27. The first mechanical coupling 27 and the second mechanical coupling 31 are locked to each other by pushing the rivet-like protrusions axially into the hook-shaped slots up to a mechanical stop and a subsequent twist around the rotor axis z to move the rivet-like protrusions into a defined locking position.

[0056] In the locking position, the first sealing element 9a is sealingly squeezed between the pump base 5 and the (lower) first axial segment end 29 of the (bottommost) first pump stage housing segment 7a. Analogously, the second sealing element 9b is sealingly squeezed between the first pump stage housing segment 7a and the (lower) first axial segment end 29 of the (topmost) second pump stage housing segment 7b. Finally, the third sealing element 9c is sealingly squeezed between the second pump stage housing segment 7b and the (lower) pump head end 35. Thereby, the fluid channels within the centrifugal pump assembly 1 are completely sealed to prevent leakage. As shown in FIG. 2a, the pump stage housing segments 7a comprise a sealing groove 30 at the (lower) first axial segment end 29, wherein the sealing elements 9a-c are positioned at least partly within the sealing groove 30. The pump head 11 also comprises a sealing groove 30 (see FIG. 1) at the (lower) pump head end 35. Before coupling the pump stage housing segments 7a,b to each other or to the pump head 11 or pump base 5, the sealing elements 9a-c protrude at least partially radially outward out of the sealing groove 30. When the pump stage housing segments 7a,b are coupled to each other or to the pump head 11 or pump base 5, the sealing elements 9a-c are sealingly squeezed radially inward by a radial inner surface 32 of the other pump stage housing segment 7a,b or pump base 5 (see FIG. 5). Alternatively, or in addition, the sealing elements 9a-c may be arranged to be squeezed axially between the components.

[0057] Due to the six-fold rotational symmetry of the mechanical couplings 27, 31, there are six distinct rotational mounting positions which may serve as the locking position. Preferably, each of the pump stage housing segments 7a,b comprises a six-fold rotational symmetry so that the six distinct rotational mounting positions may be indistinguishable from each other. This facilitates the assembly procedure and reduces the risk of incorrect assembling. A skilled person will readily understand that any m-fold rotational symmetry may be applicable to achieve this, wherein m≥2.

[0058] FIG. 2b shows that the pump stage housing segments 7a,b comprises an impeller receptacle 39 that is open towards the (upper) second first axial segment end 33. The impeller receptacle 39 is configured to completely receive one of the impellers 3b,c. The pump stage housing segment 7a,b comprises a tubular element 41 arranged in the centre for receiving the rotor shaft segment 25a-c of said impeller 3b,c.

[0059] As shown in FIG. 2b, each pump stage has its own axial and radial bearing. The tubular element 41 defines a static radial inner bearing surface 43. When the centrifugal pump assembly 1 is completely assembled, the static radial inner bearing surface 43 is in low-friction sliding contact with a corresponding rotating radial outer bearing surface 45 of the rotor shaft segment 25a-c (see FIGS. 3 and 4b). Furthermore, the pump stage housing segment 7a,b defines a static annular axial bearing surface 46 facing towards the pump head 11. When the centrifugal pump assembly 1 is completely assembled, the static axial bearing surface 46 is in low-friction sliding contact with a corresponding downward-facing, i.e. towards the pump base 5, rotating axial bearing surface 48 of the impeller 3b,c (see FIGS. 3 and 4b).

[0060] The pump base 5, when seen from the (upper) pump base end 37, looks essentially identical to FIG. 2b. The pump base 5 also comprises an impeller receptacle 39 that is open towards the (upper) pump base end 37. The impeller receptacle 39 of the pump base 5 is configured to completely receive the first impeller 3a. The pump base 5 comprises a tubular element 41 arranged coaxially within a suction mouth 51 (see FIG. 6) for receiving the rotor shaft segment 25a of the first impeller 3a. The tubular element 41 is supported within the suction eye 51 by radially extending webs 42 (see FIGS. 3, 6 and 7). The tubular element 41 of the pump base 5 defines a static radial inner bearing surface 43. When the centrifugal pump assembly 1 is completely assembled, the static radial inner bearing surface 43 is in low-friction sliding contact with a corresponding rotating radial outer bearing surface 45 of the rotor shaft segment 25a of the first impeller 3a (see FIGS. 3, 4b and 6). Furthermore, the pump base 5 defines a static annular axial bearing surface 46 facing towards the pump head 11. When the centrifugal pump assembly 1 is completely assembled, the static axial bearing surface 46 is in low-friction sliding contact with a corresponding downward-facing, i.e. towards the pump base 5, rotating axial bearing surface 48 of the first impeller 3a (see FIGS. 3 and 4b). The pump base 5 also squeezes the first sealing element 9a radially inward into the sealing groove 30 of the first pump stage housing segment 7a.

[0061] It should be noted that “low-friction sliding contact” shall mean herein that a thin lubricating film of pumped fluid may be placed between the bearing surfaces. The bearing surfaces may comprise a different material for reducing friction and wear. For example, the bearing surfaces may be coated, treated and/or mechanically processed. In case of the pump stage housing segments 7a,b and/or the impellers 3a-c being additively manufactured, multimaterial additive manufacturing (MMAM) with or without post-processing may be used to produce the bearing surfaces 43, 45, 46, 48 with a different material than the rest of the respective component it belongs to.

[0062] Radially between the tubular element 41 and the static axial bearing surface 46, there is an annular fluid outlet of a guide passage 47 defined by the internal structure of the pump stage housing segment 7a,b. The impeller 3a-c located within the impeller receptacle 39 comprises an impeller inlet 19 (see FIG. 4b) which receives pumped fluid from the fluid outlet of the guide passage 47.

[0063] Radially outward from the impeller receptacle 39, the pump stage housing segments 7a,b each have a structure defining a section of a fluid outlet channel 53. The pumped fluid is guided from the pump head 11 through the fluid outlet channel 53 downward towards the pump outlet 15. Due to the chosen six-fold rotationally symmetric configuration of the pump stage housing segment 7a,b of the shown embodiment, there are six fluid outlet channels 53 circumferentially distributed around the impeller receptacle 39. In the shown embodiment, the fluid outlet channels 53 are separate from each other before they combine in the suction mouth 51.

[0064] FIG. 3 shows the rotor shaft segments 25a-d when the centrifugal pump assembly 1 is completely assembled. The impellers 3a-c are arranged within their associated impeller receptacle 39 such that the impeller inlet 19 receives fluid being guided by the guide passage 47 essentially vertically upward. The rotor shaft segments 25a-c extend through the tubular elements 41. The rotor shaft segments 25a-d are coupled to each other by a positive fit in form of a claw coupling (see FIG. 4b). The positive fit coupling is axially loose, but allows a torque transfer. A (lower) first axial end 55 of the rotor shaft segment 25a-d comprises a positive fit coupling with an (upper) second axial end 57 of another one of the rotor shaft segments 25a-d for torque transfer between the rotor shaft segments 25a-d. The coupling portion at the (lower) first axial end 55 to the rotor shaft segment 25a of the first impeller 3a is not used. The coupling portion at the (lower) first axial end 55 of the rotor shaft segment 25b of the second impeller 3b engages with the (upper) second axial end 57 of the rotor shaft segment 25a of the first impeller 3a. The coupling portion at the (lower) first axial end 55 of the rotor shaft segment 25c of the third impeller 3c engages with the (upper) second axial end 57 of the rotor shaft segment 25b of the second impeller 3b. At least one of the rotor shaft segment 25a-d is not integral part of one of the impellers 3a-c. This is here a fourth rotor shaft segment 25d that extends towards the motor. The coupling portion at the (lower) first axial end 55 of the fourth rotor shaft segment 25d engages with the (upper) second axial end 57 of the rotor shaft segment 25c of the third impeller 3c. The torque of the motor is thereby transferred from the fourth rotor shaft segment 25d to other rotor shaft segments 25a-c.

[0065] There is a small axial buffer room 59 provided between the first axial end 55 of the rotor shaft segment 25a-d the second axial end of the next rotor shaft segment 25a-c. The axial buffer room 59 is at least partly filled by a buffer medium, e.g. air, pumped fluid, an elastomer, or a combination thereof.

[0066] FIG. 4a,b show the impeller 3a-c in more detail. The impeller 3a-c has a structure defining impeller fluid channels spiralling radially outward and S-shaped upward from the impeller inlet 19 to the impeller outlet 21. The impeller inlet 19 faces towards the pump base 5, i.e. downward. The impeller outlet 21 faces towards the pump head 11, i.e. upward. The impeller fluid channels within the impellers 3a-c are separated from each other by 16 impeller vanes 23. When the centrifugal pump assembly 1 is completely assembled, a fluid inlet of the guide passage 47 within the pump stage housing segment 7a,b receives from the impeller outlet 21 fluid flowing essentially vertically upward.

[0067] In FIG. 5, the flow of the pumped fluid is indicated by large arrows. As can be seen, each pump stage housing segment 7a,b defines a guide passage 47 for receiving pumped fluid from an impeller outlet 21 and guiding the pumped fluid radially inward along an S-shaped path towards an impeller inlet 19 of the subsequent impeller 3a-c. The impeller outlet 21 faces away from the pump base 5 and an inlet of the guide passage 47 faces towards the pump base 5. Analogously, the impeller inlet faces away from the pump head 11 and an outlet of the guide passage faces away from the pump base 5. Thereby, the pumped fluid flows essentially axially (vertical) at the interfaces between the impeller 19 and the guide passage 47.

[0068] Each pump stage housing segment 7a,b also defines a section of the outlet fluid channel 53 through which the pumped fluid flows essentially downward towards the pump outlet 15. As shown in FIG. 5, the outlet fluid channel 53 has a wavy shape which may be optimised for fluid dynamic efficiency and/or structural integrity at the cost of minimal material and weight. Additive manufacturing of the pump stage housing segments 7a,b significantly increase the design freedom in this respect. The outlet fluid channel 53 may, however, have a different shape, e.g. a straight vertical shape, if that is more suitable for any reason.

[0069] FIG. 6 shows the pump base 5 in more detail. As already explained above, the pump base 5 functions partly as a pump housing for the first pump stage. Therefore, the pump base 5 comprises the impeller receptacle 39 that is open towards the (upper) pump base end 37. The first impeller 3a is completely received within the impeller receptacle 39 of the pump base 5. In other words, the pump base 5 completely surrounds the first impeller 3a. The tubular element 41 of the pump base 5 is arranged coaxially within the suction mouth 51 for receiving the rotor shaft segment 25a of the first impeller 3a. The tubular element 41 is supported within the suction eye 51 by radially extending webs 42. The tubular element 41 of the pump base 5 defines a static radial inner bearing surface 43. The static radial inner bearing surface 43 is in low-friction sliding contact with a corresponding rotating radial outer bearing surface 45 of the rotor shaft segment 25a of the first impeller 3a. Furthermore, the pump base 5 defines a static annular axial bearing surface 46 facing towards the pump head 11. The static axial bearing surface 46 is in low-friction sliding contact with a corresponding downward-facing, i.e. towards the pump base 5, rotating axial bearing surface 48 of the first impeller 3a (see FIGS. 3 and 4b).

[0070] FIG. 7 shows an embodiment, in which the pump stage housing segments 7a,b have a structure defining only a part of a wall section of the fluid outlet channel 53, so that the pumped fluid flows along an outer periphery of the pump stage housing segments 7a,b downwards towards the pump outlet 15. The centrifugal pump assembly 1 further comprises a fluid outlet channel sleeve 61 circumferentially enclosing the pump stage housing segments 7a,b in order to define the rest of the wall section of the fluid outlet channel 53, so that the pumped fluid flows along an inner surface of the fluid outlet channel sleeve 61, i.e. radially between the pump stage housing segment 7a,b and the fluid outlet channel sleeve 61, downwards towards the pump outlet 15. In other words, the part of the wall section defined by the pump stage housing segments 7a,b and the fluid outlet channel sleeve 61 complement each other to define the at least one fluid outlet channel 53. The rest of the embodiment is identical to the previously described embodiment of FIGS. 1 to 6.

[0071] The embodiment shown in FIG. 7 is particularly advantageous for centrifugal pump assemblies with many pump stages, because there is no sealing element 9b needed between the pump stage housing segments 7a,b. The first sealing element 9a may be used to seal a gap between the fluid outlet channel sleeve 61 and the pump base 5. Analogously, the (topmost) third sealing element 9c may be used to seal a gap between the fluid outlet channel sleeve 61 and the pump head 11. Thus, only two sealing elements 9a,c are needed here independent of the number of pump stages. The more pump stages there are, the more sealing elements 9b may be saved, which reduces the number of parts and the risk of a sealing leakage. It should be noted that the fluid outlet channel sleeve 61 does not pull the pump head 11 and the pump base 5 together. This is, as described for the embodiment of FIGS. 1 to 6, achieved by the mechanical coupling of the pump stage housing segments 7a,b to each other and to the pump base 5 and to the pump head 11, respectively.

[0072] FIG. 8 shows an embodiment of a three-stage vertical centrifugal pump assembly 1 in a full longitudinal cut view showing particularly an embodiment of the pump head 11. The pump head 11 may be structurally integral with a motor housing 63 or connected to it as shown in FIG. 8. The pump head 11 is connected with its (lower) pump head end 35 to the (topmost) pump stage housing segment 7b and with an opposite pump head end 65 to the motor housing 63. The motor housing 63 encloses an electric motor, preferably a permanent-magnet synchronous motor (PMSM), comprising a rotor 67 being fixed to the (topmost) rotor shaft segment 25d and a stator 69 surrounding the rotor 67.

[0073] The motor housing 63 defines a reverse channel 71 for receiving pumped fluid from the last (topmost) impeller 3c and directs the pumped fluid to the section of the fluid outlet channel 53 defined by the (topmost) second pump stage housing segment 7b that is coupled to the pump head 11. The motor housing 63 functions as a heat sink being in thermal contact with heat-generating electric components of the motor or of control electronics for controlling the motor. In order to cool the motor housing 63 for improving heat dissipation, the reverse channel 71 extends through the motor housing 63 in thermal contact with heat-generating components of the motor, so that the pumped fluid cools the heat-generating components of the motor. Preferably, there is one reverse channel 71 provided for each fluid outlet channel 53, i.e. six reverse channels 71 in the shown embodiment. Each reverse channel 71 may follow a U-shaped path within the motor housing 63 extending essentially along the full axial length of the stator 69, wherein the reverse channel 71 comprises an upward section and a downward section. The longitudinal cut view of FIG. 8 only shows two downward sections of two of the reverse channels 71, because the upward sections and the other four reverse channels 71 are outside of the cutting plane. The downward sections of the reverse channels 71 feed the fluid outlet channels 53 to guide the pumped fluid downward towards the pump outlet 15.

[0074] Where, in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present disclosure, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the disclosure that are described as optional, preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims.

[0075] The above embodiments are to be understood as illustrative examples of the disclosure. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. While at least one exemplary embodiment has been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art and may be changed without departing from the scope of the subject matter described herein, and this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

[0076] In addition, “comprising” does not exclude other elements or steps, and “a” or “one” does not exclude a plural number. Furthermore, characteristics or steps which have been described with reference to one of the above exemplary embodiments may also be used in combination with other characteristics or steps of other exemplary embodiments described above. Method steps may be applied in any order or in parallel or may constitute a part or a more detailed version of another method step. It should be understood that there should be embodied within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of the contribution to the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the disclosure, which should be determined from the appended claims and their legal equivalents.

LIST OF REFERENCE CHARACTERS

[0077] 1 centrifugal pump assembly [0078] 3a-c impellers [0079] 5 pump base [0080] 7a,b pump stage housing elements [0081] 9a-c sealing elements [0082] 11 pump head [0083] 13 pump inlet [0084] 15 pump outlet [0085] 17 feet [0086] 18 openings [0087] 19 impeller inlet [0088] 21 impeller outlet [0089] 23 vanes [0090] 25a-d rotor shaft segments [0091] 27 first mechanical coupling [0092] 29 first axial segment end [0093] 31 second mechanical coupling [0094] 33 second axial segment end [0095] 35 pump head end [0096] 37 pump base end [0097] 39 impeller receptacle [0098] 41 tubular element [0099] 42 webs [0100] 43 static inner radial bearing surface [0101] 45 rotating outer radial bearing surface [0102] 46 static axial bearing surface [0103] 47 guide passage [0104] 48 rotating axial bearing surface [0105] 51 suction eye [0106] 53 fluid outlet channel [0107] 55 first axial end of a rotor shaft segment [0108] 57 second axial end of a rotor shaft segment [0109] 59 axial buffer room [0110] 61 fluid outlet channel sleeve [0111] 63 motor housing [0112] 65 pump head end [0113] 67 rotor [0114] 69 stator [0115] 71 reverse channel [0116] z rotor axis