EP2818725B1 - Centrifugal pump with axially shiftable and closable impeller - Google Patents

Description

The invention relates to a centrifugal pump unit and an impeller for such a centrifugal pump unit.

There are known centrifugal pump units, which have an axially displaceable shaft, whereby the impeller can be brought into two axial positions, wherein in a first position, the flow path closed by the impeller and in a second position, the flow path through the impeller is opened. Such an arrangement is for example off DE 101 15 989 A1 known. In the first position, in which the flow path is closed by the impeller, the impeller is held by spring force, while it is drawn when energized by the drive motor by a resulting axial magnetic force against the spring force in the second position. Ie. In order to open the impeller and the pump, it is necessary that the drive motor has a special configuration which generates a magnetic axial force for moving the impeller when energized.

DE 21 07 000 discloses a centrifugal pump with an axially displaceable impeller to selectively bring the impeller into fluid communication with two different inputs. In this case, the impeller is designed so that it is moved during operation of the pump unit by the hydraulic pressure in one of the possible switching positions and can be moved via an electromagnetic coil in the motor either against this hydraulic force in a second switching position.

DE 93 19 309 U1 discloses a pump having an electric drive motor in which the impeller is axially movable to be selectively moved to a closed or opened position. In this case, the impeller can be moved by a magnetic force or a hydraulic force in the closed position and open automatically during operation of the pump unit by an opposite hydraulic pressure. Alternatively, the impeller can be held by an axial centering of the rotor in the stator during operation in an open position and moved in the de-energized state by an additional spring or an additional magnet in a closed switching position.

EP 2 228 891 A2 discloses an electric motor for actuating a valve with a pump impeller, which simultaneously forms a movable valve member. In this case, the pump impeller can be moved by normal to the operation of the pump impeller opposite direction of rotation via a thread in a closed switching position.

DE 25 10 787 A1 discloses a pump unit with an impeller, which can be selectively moved to a closed or open switching position. The impeller is axially movable together with the rotor of the drive motor. The rotor has a conical configuration, so that it is moved by the prevailing magnetic forces in operation in an axial position, which moves the impeller in its open position. The provision is made via a spring.

DE 10 2010 062 752 A1 discloses another pump unit with an axially movable impeller, which is movable between an open and a closed switching position. For movement, an additional hydraulic system is provided.

All of the above-described solutions have in common that in order to move the impeller into at least one of the two possible switching positions an additional actuating element such as a magnet, a spring or a hydraulic system is required or in the system a hydraulic pressure must prevail to the impeller in its closed Keep switching position.

In view of the cited prior art, it is an object of the invention to provide a centrifugal pump unit, which allows a displacement of the impeller between a first and a second functional position without additional components and makes it possible to keep the impeller without hydraulic pressure in one of the functional positions.

This object is achieved by a centrifugal pump assembly having the features specified in claim 1. Preferred embodiments emerge from the subclaims, the following description and the accompanying figures.

The centrifugal pump unit according to the invention has an electric drive motor, which is preferably designed as a permanent magnet rotor. The drive motor is preferably a canned motor, i. H. a wet running engine. The drive motor drives at least one impeller. In this case, the impeller can be connected via a shaft to the rotor of the drive motor. Alternatively, it is possible that the impeller is also directly connected to a shaftless rotor or integrally formed with at least a part of the rotor. According to the invention, the impeller is movable in the axial direction between at least two functional positions. In this case, the movement of the impeller preferably takes place together with the shaft or the rotor of the electric drive motor. In a first functional position, a flow path through the impeller is substantially closed, so that the impeller can assume a valve function in this functional position and can substantially block a flow path through the centrifugal pump assembly. The shut-off essentially means that a small residual pass can remain and may even be desirable, as set forth below. In another functional position in which the impeller is axially displaced, however, the flow path through the impeller and thus through the centrifugal pump unit is open and the centrifugal pump unit can promote the drive of the electric drive motor by rotation of the at least one impeller, a fluid, in particular a liquid.

According to the invention it is now provided that the impeller is held in a first functional position by a magnetic force, in particular a permanent magnetic force. From the first to the second functional position, the impeller can then according to the invention be moved by a hydraulic force and held in the second position by a hydraulic force. This hydraulic force is a hydraulic force generated by a fluid delivered by the impeller. Ie. Here, the impeller generates, when it is driven by the drive motor, the output pressure, which in turn acts on the impeller and / or coupled to the impeller for power transmission component that acts on the impeller, a hydraulic force, it in the second Function position holds. Thus, in a very simple manner by driving the drive motor, ie by commissioning the drive motor, the impeller can be moved axially to open the flow passage.

The impeller is held in the first operative position by a permanent magnetic force acting between a permanent magnet rotor connected to the impeller and the surrounding stator of the drive motor. So can be dispensed with additional components for generating a permanent magnetic force. In addition, these Kratterzeugungsmittel are substantially free of wear, so that a high reliability of the pump unit according to the invention is ensured. The impeller is held in the first functional position by a permanent magnetic force, which results from an axial displacement of the permanent magnet rotor relative to the stator of the drive motor. A permanent magnet rotor tends in the axial direction to center in the iron circle of the stator in the axial direction. If now the rotor is moved out of this centered position in the axial direction, this leads to a permanent magnetic restoring force, which tends to pull the rotor back to the centered position. According to the invention, this permanent-magnet restoring force is used to hold the impeller in the first functional position and to move it, if necessary, from the second functional position into the first functional position, when the hydraulic force which drives the impeller in the second functional position holds, falls away. Ie. In this embodiment, the centrifugal pump unit is designed so that the hydraulic force which holds the impeller in the second functional position is greater than the permanent magnetic force which holds the impeller in the first functional position. This then causes the hydraulic axial force is eliminated when switching off the drive motor and the impeller is moved by the permanent magnetic force back into the first functional position. When the drive motor is switched on, the impeller generates a pressure on the output side and the said hydraulic axial force is built up, which is greater than the permanent magnet reset angle, so that the impeller is then moved from the first functional position to the second functional position.

According to the invention, the flow path through the impeller is closed in the first functional position and opened in the second functional position. In addition, in the first functional position, the impeller is preferably located closer to the stator than in the second functional position. In the second functional position, the impeller is preferably moved further to the suction side than in the first functional position. Here, however, a reverse configuration is possible.

Further, a closure element is preferably present, which in the functional position in which the flow path is closed by the impeller, at least a large part, preferably more than 90%, closes an outlet opening or inlet opening of the impeller. The closing element thus achieves the closing of the flow path, it being possible, as described above, that in the flow path, a residual opening remains, which allows a flow when starting the impeller in the closed or locked functional position to ensure a pressure build-up on the output side of the impeller in this functional position to the desired hydraulic force for moving the impeller in the create second functional position. Such residual opening is preferably less than 10% of the total flow path, more preferably less than 5% or 2% of the total flow path. However, such residual opening is tolerable in many applications where shut-off of the flow path is desired. More preferably, the centrifugal pump unit is designed such that the closure element in that functional position in which the flow path is substantially closed by the impeller, the inlet opening or the outlet largely, but only so far closes that when starting the impeller, a pressure build-up on the output side of the impeller is possible. Ie. the residual opening of the impeller is preferably as small as possible, but as large as necessary to set pressure in the closed state.

In order to enable opening and closing of the flow path through the closure element, the impeller is preferably movable between the first and the second functional position relative to the closure element. In this case, the closure element is preferably stationary and the impeller, as described, axially displaceable. The closure element may preferably surround the impeller circumferentially and the impeller immerses with its outer wall in the inner circumference of the closure element.

According to a further preferred embodiment of the invention, the impeller may have an axial-side or radial-side inlet opening and the closure element may substantially cover the inlet opening in a functional position in order to close the closure the flow path through the impeller, wherein, as described above, a certain residual opening, preferably less than 10% or 5%, more preferably less than 2% may remain. If the inlet opening is located on the axial side, the closure element is preferably aligned so that it extends transversely to the longitudinal or rotational axis of the impeller and the end face closes the inlet opening. In the event that the inlet opening is located radially on the side, preferably as an annular inlet opening extending over the outer circumference of the impeller, the closure element is preferably designed as an annular wall which can cover the outer circumference of the impeller.

According to a further possible embodiment, the impeller may have a radial outlet opening and cover the closure element in a functional position, the outlet opening. Ie. In this embodiment, the centrifugal pump unit is designed so that the flow path is effected by the impeller by closing the radial or peripheral outlet opening. The closure element is preferably designed as an annular wall, which in a functional position, d. H. the functional position, in which the flow path is substantially closed, surrounding the outlet opening circumferentially. Here too, a residual opening may remain in the manner described above.

According to a further preferred embodiment, the centrifugal pump assembly is designed such that in the functional position in which the flow path is closed by the impeller, the impeller rests with a peripheral edge bounding the outlet opening at an end edge of the annular wall. Thus, the flow path between the first peripheral edge, which preferably faces the other functional position, and the annular wall are preferably substantially sealed tight. However, more preferred may be between a second peripheral edge opposite this first peripheral edge and the annular wall in that functional position in which the flow path through the impeller is substantially closed, a flow passage remains which is open to an axial end face of the impeller. This is preferably a pressure-side axial end face on the outside of the impeller. More preferably, this axial end face is preferably located in a space enclosed by the annular wall, which, when the impeller rests with its first end edge, which limits the outlet opening, on the annular wall, is completely closed to a pressure channel. In this way the flow path to the outside is completely interrupted. However, there remains a flow path from the outlet side of the impeller to a pressure-side end face, so that upon rotation of the impeller in this area can build up a pressure which acts on the end face of the impeller and thus generates a hydraulic force which the impeller from this functional position in the other functional position, if necessary, shifts against an acting permanent magnetic force or spring force.

In addition, a special impeller for a centrifugal pump unit is advantageous for the invention. This impeller may find particular use in a centrifugal pump unit, as described above, but could also be used independently in another centrifugal pump unit. The impeller has at least one outlet opening and an inlet opening. An essential feature is that the inlet opening is not located on the axial side but in a peripheral portion of the impeller, ie, is open to the outer circumference and the radial side. Such an impeller allows the valve function described above, but could not only be used to close the flow path, but also, for example, by axial displacement between two possible Change or switch flow paths or cause a mixing function.

Particularly preferably, this impeller has a closed suction-side axial end face, on which the peripheral portion adjoins the inlet opening. Ie. The fluid to be delivered flows essentially not in the axial direction but substantially in the radial direction through the inlet opening into the impeller. The closed axial end side on the suction side of the impeller can simultaneously take over the function of a control disk by different hydraulic pressures acting on both sides of this end face, d. H. once on the inside of the impeller and once on the opposite outside of the impeller. These hydraulic forces can be used for axial positioning or displacement of the impeller, depending on which side of the impeller, a larger force acts. The closed axial end face may be formed in one piece or in one piece with the other parts of the impeller. However, it is also possible to form this closed side in the form of a separate disc, which is fixed directly on a shaft of the rotor, as well as the impeller. Such a disk can be arranged axially spaced from the impeller, so that a gap remains between the disk and the suction-side axial end of the impeller, which forms the annular radial-side inlet opening. Thus, with a conventional impeller with an axial inlet opening and an additional element, namely the disc, an impeller according to the invention can be created, which has an opening which is open to the outer circumference.

According to a further preferred embodiment, the inlet opening is formed as a extending over the entire circumference of the impeller annular opening. In this case, webs may optionally be formed in the opening in the axial direction, which the Circumferential edges bounding the opening connect together to stabilize the structure of the impeller. Alternatively or additionally, for example, a closed axial end face of the impeller may be connected to the remaining parts of the impeller via the shaft or a connecting element in the interior of the impeller to ensure a connection across the annular opening. The described opening preferably has a surface which corresponds to 50 to 150% of the cross-sectional area in the interior of the impeller in this area, this cross-sectional area extending transversely to the longitudinal or rotational axis of the impeller. The opening of the impeller is preferably chosen so large that no high flow velocities occur in this area.

More preferably, the impeller has on its suction side an elongated cylindrical portion of constant cross section, which preferably has an outer surface which corresponds to a size of 50 to 150% of an inner cross section (transverse to the longitudinal axis of the impeller) in the interior of this section. In this cylindrical portion, the above-described annular or radially opened opening, which forms the inlet opening of the impeller, are located. The cylindrical portion of the impeller permits axial movement of the impeller in a pump set as described above, wherein the entry portion in each position of the impeller can be sealed sufficiently outwardly to surround the pressure and suction sides of the impeller in each To separate position from each other.

Fig. 1

schematisch die erste Ausführungsform der Erfindung, mit dem Laufrad in einer ersten Funktionsstellung,

Fig. 2

schematisch ein Kreiselpumpenaggregat gemäß Fig. 1 mit dem Laufrad in einer zweiten Funktionsstellung,

Fig. 3

schematisch eine zweite Ausführungsform eines erfindungsgemäßen Kreiselpumpenaggregates mit dem Laufrad in einer ersten Funktionsstellung und

Fig. 4

das Kreiselpumpenaggregat gemäß Fig. 3 mit dem Laufrad in seiner zweiten Funktionsstellung.

The invention will now be described by way of example with reference to the accompanying drawings. In these shows:

Fig. 1

schematically the first embodiment of the invention, with the impeller in a first functional position,

Fig. 2

schematically a centrifugal pump unit according to Fig. 1 with the impeller in a second functional position,

Fig. 3

schematically a second embodiment of a centrifugal pump assembly according to the invention with the impeller in a first functional position and

Fig. 4

the centrifugal pump unit according to Fig. 3 with the impeller in its second functional position.

The pump unit according to the first embodiment in FIGS. 1 and 2 has an electric drive motor 2, which has a stator 4 and a rotor 6 rotatable about the longitudinal axis X therein. The drive motor is designed as a wet-running motor and has a gap tube 7 between the stator 4 and the rotor 6. This can be formed completely closed and separates rotor space and stator space. The rotor is designed as a permanent magnet rotor 6 and rotatably connected to a along the longitudinal axis X extending shaft 8, which is preferably made of ceramic and machined over its entire length to storage quality. The shaft in turn is non-rotatably connected to an impeller 10, which is preferably formed of plastic. The rotor 6 is arranged axially movable together with the shaft 8 and the impeller 10 in its bearings 12, so that the impeller in a Fig. 1 shown first axial functional position and an in Fig. 2 shown axially spaced second functional position can take. In this case, the impeller is closer to the stator 4 in the first functional position than in the second functional position.

The impeller 10 has on its axial end face an inlet opening 14 in the form of a suction mouth. Through this, a fluid to be conveyed, in particular a liquid to be conveyed in the axial direction X in the Inflow impeller 10. In the impeller 10, the flow is then accelerated radially outwards by the centrifugal forces prevailing during rotation of the impeller and can emerge from the impeller 10 through a peripheral outlet opening located at the axial end facing away from the inlet opening 14. The outlet opening 16 is formed as an annular opening in the peripheral region of the impeller adjacent to a pressure-side axial end face 18 of the impeller.

In the in Fig. 1 shown first functional position, the outlet opening 16 is closed by a closure element in the form of a ring wall 20. The annular wall 20 extends starting from a wall bounding the pump chamber, in this case a bearing carrier 22 in a direction away from the stator 4. In this case, the annular wall 20 has such an axial length that it completely covers the axial extent of the outlet opening 16 in the first functional position and comes into contact with a first peripheral edge 24 which limits the outlet opening 16 on one axial side. The first peripheral edge 24 is the suction side of the impeller 10 facing the peripheral edge which limits the outlet opening 16. The closer to the pressure side lying opposite second peripheral edge 26, which limits the outlet opening 16 to the pressure-side axial end, has a smaller diameter than the first peripheral edge 24 with respect to the longitudinal axis X and lies in the first functional position in such a way inside the annular wall 24, that between the inner circumference of the annular wall 24 and the second peripheral edge 26, an annular gap 28 remains. The annular gap 28 forms a flow passage from the interior of the impeller through the outlet opening 16 to the pressure-side end face 18 of the impeller 10. This flow path is open even when the annular wall 20 abuts the first peripheral edge 24 and so the flow path through the impeller to the outside in a pressure channel 30 closes. Thus, in the first functional position, although no fluid from the suction channel 32 in the Pressure channel 30 flow, however, when the impeller is rotated by driving the drive motor 2, in the space inside the annular wall 20 adjacent to the pressure-side end face 18 and pressure-side cover plate of the impeller 10. So in this area when starting the impeller from the first functional position, which in Fig. 1 is shown, a pressure and a hydraulic axial force F _H generated which acts parallel to the longitudinal axis X on the pressure-side end face 18 of the impeller 10 and so the impeller 10 in the direction A in the in Fig. 2 shifts shown second functional position.

In this second functional position, the outlet opening 16 is displaced in the axial direction outside of the annular wall 20, ie the peripheral edge 24 has been disengaged from the end edge of the annular wall 20 and the annular wall 20 substantially no longer overlaps the annular outlet opening 16, so that during rotation of the impeller 10 funded fluid from the outlet opening 16 can escape into the pressure channel 30. In this case acts on the pressure-side end face 18 of the impeller 10 further, the hydraulic force F _H due to the pressure in the pressure channel 30. This hydraulic force F _H keeps the impeller 10 in the in Fig. 2 shown second functional position.

In the first functional position is, as in Fig. 1 shown, the rotor 6 centered with respect to the surrounding stator 4 in the axial direction X, that is, the axial center S of the stator and the axial center R of the rotor are substantially one above the other. If the rotor, as in Fig. 2 shown, the dimension a is shifted relative to the stator 4, to bring the impeller 10 in the second functional position shown, thereby shifts the axial center R of the rotor 6 relative to the axial center S of the stator 4 also by the dimension a, as in Fig. 2 shown. This results in a magnetic restoring force F _M. This is because the rotor 6 is a permanent magnet rotor to a permanent magnetic force. The magnetic restoring force F _M endeavors to restore the rotor 6 in the in Fig. 1 to move shown axially centered position. Ie. the magnetic restoring force F _M counteracts the hydraulic force F _H. As long as the hydraulic force F _{H is} greater than this magnetic restoring force F _M , the impeller 10 remains in the in Fig. 2 shown second functional position. By appropriate dimensioning of the drive motor and the impeller 10, this can be ensured. In addition, the drive motor 2 can be controlled so that always a sufficient pressure in the pressure channel 30 is ensured in order to keep the impeller 10 in operation in the second functional position shown. When the drive motor 2 is turned off, the hydraulic axial force F _H falls away and it only affects the magnetic restoring force F _M , whereby then the impeller 10 via the shaft 8 together with the rotor 6 back into the in Fig. 1 shown starting position is moved back, in which the impeller 10 is then in the first functional position, in which the outlet opening 16 is closed by the annular wall 20.

If the drive motor is not controlled so that the pressure in the pressure channel 30 is always such that the impeller in operation in its second in Fig. 2 shown functional position, an automatic mechanical quantity limitation can be achieved. If the pump unit in a high flow and low pressure operating state, this then causes the pressure in the pressure channel 30 decreases so much that the hydraulic force F _{H is} smaller than the magnetic restoring force F _M and the impeller 10 in the direction of his first functional position, which in Fig. 1 shown is moved. In this case, the outlet opening 16 of the impeller is then at least partially closed, so that the flow through the impeller is reduced. In this case, then the output side of the impeller in the pressure channel 30 again set a pressure which counteracts the magnetic restoring force F _M and the impeller 10 in its second functional position or in a functional position between the first and the second Function position holds. Such a configuration is advantageous if the pump unit has no electronic quantity limitation and, for example, is not externally controllable in order to reduce the flow rate in certain operating conditions.

Fig. 3 and 4 show a second embodiment of the invention. At the in Fig. 3 and 4 shown centrifugal pump unit, the drive motor 2 is identical to the in Fig. 1 and 2 formed Ausführungsbespiel, so reference is made to the relevant description. Also, this drive motor 2 is designed so that by moving the rotor 6 relative to the stator 4 by the dimension a, the axial center of the rotor 6 from the axial center S of the stator 4 is out of control, so that a magnetic restoring force F _M results as previously described in the first embodiment.

The second embodiment differs from the first embodiment in that of the impeller 10 ', which is connected to the shaft 8, not the outlet opening 16' but the inlet opening 14 'is closed in the first functional position. According to this embodiment, the outlet opening 16 'remains in fluid communication with the pressure channel 30 in both functional positions. However, in the first functional position, which in FIG Fig. 3 is shown, the connection between the suction channel 32 'and the inlet opening 14' is substantially closed.

The inlet opening 14 'is formed in this impeller 10' according to the invention as a peripheral or radial inlet opening 14 '. The inlet opening 14 'forms a circumferential annular opening through which fluid in the radial direction in the interior of the impeller 10' can occur. The suction-side end face 34 of the impeller 10 'is formed closed. The suction-side end face 34 is formed by a disk-shaped wall, which at the same time has the function of a control disk can take over, since on the two sides of the suction-side end face 34, that is, both the interior of the impeller facing surface and the outwardly directed surface, a hydraulic pressure can act. In the first functional position, the inlet opening 14 'is located so that it faces an annular wall 36 in the pump chamber or pump housing. The annular wall 38 is formed concentrically to the longitudinal axis X and surrounds the annular inlet opening 14 'so that it is substantially completely covered. However, the inner diameter of the wall 36 is slightly larger than the outer diameter of the opening 14 'adjacent circumferential surfaces, so that between the wall 16' and the inlet opening 14 'bounding peripheral edge an annular gap 38 remains. This forms a residual opening when the flow path through the impeller 10 'is substantially closed in the first functional position. However, this residual opening represents less than 2% of the area of the inlet opening 14 ', so that only a very small flow passage remains. The flow passage through the gap 38 is dimensioned so that here just as much fluid or liquid in the first functional position according to Fig. 3 can flow through that when starting the impeller 10 'can build up a pressure in the pressure channel 30. Such a pressure leads to a hydraulic axial force F _H , which acts on the pressure-side cover plate or front side 18 'from the outside to the impeller 10', so that this in the direction A from the first functional position in the in Fig. 4 shown second functional position is moved.

In this second functional position, the inlet opening 14 'is opposite the suction channel 32, so that the suction channel 32' through the inlet opening 14 'with the interior of the impeller 10' is in fluid communication and the impeller 10 'promotes fluid or fluid in rotation in the usual way , In this case, the hydraulic axial force F _{H continues} to act on the pressure-side cover disk or end face 18 ', so that when there is sufficient Pressure in the pressure channel 30, the impeller 10 'is held in this second functional position against the magnetic restoring force F _M. Preferably, the drive motor 2 is controlled so that always a sufficient output-side pressure in the pressure channel 30 is ensured. If the drive motor 2 is turned off and the impeller 10 'thus promotes no more fluid, the hydraulic axial force F _H falls away and the impeller 10' is returned via the shaft 8 together with the rotor 6 by the magnetic restoring force F _M back into the in Fig. 3 shown first functional position moves.

LIST OF REFERENCE NUMBERS

2

drive motor

4

stator

6

rotor

7

canned

8th

wave

10, 10 '

Wheel

12

camp

14, 14 '

inlet opening

16, 16 '

outlet opening

18

pressure-side end face

20

annular wall

22

bearing bracket

24

first peripheral edge

26

second peripheral edge

28

annular gap

30

pressure channel

32, 32 '

suction

34

suction side end face

36

wall

38

gap

X

longitudinal axis

F _H

Axial force

F _M

Restoring force

A

direction

a

offset

S

Axial center of the stator

R

Axial center of the rotor

Claims (9)

1. A centrifugal pump assembly with an electric drive motor (2) and with at least one impeller (10; 10') which is movable in the axial direction (X) between at least two functional positions, wherein in a first functional position a flow path through the impeller (10; 10') is essentially closed and in a second functional position the flow path through the impeller (10; 10') is opened, wherein the impeller (10; 10') in the first functional position is held by a permanent-magnetic force (F_M) which acts between a permanent magnet rotor (6) which is connected to the impeller (10, 10') and which is axially movable together with this and the surrounding stator (4) of the drive motor (2), said permanent-magnetic force resulting from an axial offset (a) of the permanent magnet rotor (6) relative to the stator (4) of the drive motor (2), and in the second functional position is held by a hydraulic force (F_H) which is produced by fluid delivered by the impeller and which is larger than the permanent-magnetic force (F_M).
2. A centrifugal pump assembly according to the preceding claim, characterised in that a closure element (20; 36) is present, said closure element in that functional position, in which the flow path through the impeller (10') is closed, closing an outlet opening (16) or an inlet opening (14') of the impeller (10; 10') at least for the larger part, preferably by more than 90 %.
3. A centrifugal pump assembly according to claim 2, characterised in that the closure element (20; 36) in that functional position, in which the flow path through the impeller (10; 10') is closed, closes the inlet opening (14') or the outlet opening (16) for the larger part, but closes it only to the extent that a pressure build-up at the outlet side of the impeller (10; 10') is possible on starting the impeller (10; 10').
4. A centrifugal pump according to claim 2 or 3, characterised in that the impeller (10; 10') is movable relative to the closure element (20; 36) between the first and the second functional position.
5. A centrifugal pump assembly according to one of the claims 2 to 4, characterised in that the impeller (10') comprises an axial-side or radial-side inlet opening (14') and the closure element (36) covers the inlet opening in one functional position.
6. A centrifugal pump assembly according to one of the claims 2 to 5, characterised in that the impeller (10) comprises a radial-side outlet opening (16), and the closure element (26) covers the outlet opening (16) in one functional position.
7. A centrifugal pump assembly according to claim 6, characterised in that the closure element (20) is designed as an annular wall which peripherally surrounds the outlet opening (16) in one functional position.
8. A centrifugal pump assembly according to claim 7, characterised in that in that functional position, in which the flow path through the impeller (10) is closed, the impeller (10) bears with a first peripheral edge (24) which delimits the outlet opening (16), on a face edge of the annular wall (20).
9. A centrifugal pump assembly according to claim 8, characterised in that in that functional position, in which the flow path through the impeller (10) is closed, a flow passage (28) which is open to an axial face side (18) of the impeller (10) remains between a second peripheral edge (26) which lies opposite the first peripheral edge (24) and the annular wall (20).

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