Centrifugal pump having axially moveable impeller wheel for conveying different flow paths

Abstract

A pump assembly (2) includes an electric drive motor (14) and with at least one impeller (18) which is driven by the motor. The impeller is movable in an axial direction (X) between at least one first and one second position. The impeller in the first axial position is situated in a first flow path through the pump assembly and delivers a fluid through this first flow path. The impeller in the second position is situated in a second flow path through the pump assembly and delivers a fluid through this second flow path. The pump assembly (2) is configured such that a movement of the impeller (18), between the first and the second position at least in one direction, is effected by a hydraulic force which acts on the impeller (18) and is produced by the delivered fluid. A heating installation is provided with such a pump assembly.

Claims

1. A pump assembly comprising: an electric drive motor; at least one impeller driven by the electric drive motor, wherein: the at least one impeller is movable in an axial direction between at least one first axial position and a second axial position; the at least one impeller in the first axial position is situated in a first flow path through the pump assembly and delivers fluid through the first flow path; the at least one impeller in the second axial position is situated in a second flow path through the pump assembly and delivers a fluid through the second flow path; the pump assembly is configured such that a movement of the at least one impeller between the first axial position and the second axial position at least in one direction is effected by a hydraulic force which acts on the at least one impeller and is produced by the delivered fluid; the pump assembly is configured such that the hydraulic force can be produced by differently accelerations of the electric drive motor; the at least one impeller is maintained in the at least one first axial position via a first acceleration; the at least one impeller is moved to the second axial position via a second acceleration.

2. A pump assembly according to claim 1, wherein the pump assembly is configured such that the at least one impeller on operation is held in at least one of the positions by at least one hydraulic force produced by the delivered fluid.

3. A pump assembly according to claim 1, wherein the pump assembly is configured such that the at least one impeller on operation is held in at least one of the positions by way of an interaction of at least one hydraulic force produced by the delivered fluid, of a spring force or an axially acting magnetic force or any combination of the at least one hydraulic force, the spring force and the axially acting magnetic force, wherein the magnetic force acts on a rotor of the drive motor which is connected to the at least one impeller.

4. A pump assembly according to claim 1, wherein the at least one impeller is connected to a rotor of the electrical drive motor, and at least one magnetic force acting on the at least one impeller in the axial direction results from a magnetic interaction between the rotor and a surrounding stator from an axial shift between the rotor and the stator, the at least one impeller being maintained in the first position via the at least one magnetic force and the hydraulic force.

5. A pump assembly according to claim 1, wherein the at least one impeller in the first axial position is arranged such that the at least one impeller delivers into a first exit channel, and the at least one impeller in the second axial position is arranged such that the at least one impeller delivers into a second exit channel.

6. A pump assembly according to claim 1, wherein the at least one impeller in the first axial position is arranged such that the at least one impeller is connected at a suction side to a first inlet channel, and the at least one impeller in the second axial position is arranged such that at the suction side the at least one impeller is connected to a second inlet channel.

7. A pump assembly according to claim 1, wherein the pump assembly is configured such that the hydraulic force can be produced by the electric drive motor by way of a speed change.

8. A pump assembly according to claim 1, wherein the pump assembly is configured as a bistable system, in which the at least one impeller on operation is held in the first axial position or the second axial position by way of the acting hydraulic or magnetic forces or both the hydraulic and magnetic forces.

9. A pump assembly according to claim 1, wherein the at least one impeller in the first axial position is situated axially closer to the stator of the electric drive motor than in the second axial position.

10. A pump assembly according to claim 1, wherein the pump assembly is configured such that in the first axial position of the at least one impeller, a hydraulic force acting in a direction of the first axial position acts on a suction-side, axial face side of the at least one impeller or of a pressure element which is coupled to the at least one impeller in a force-transmitting manner.

11. A pump assembly according to claim 1, wherein the pump assembly is configured such that in the first position of the at least one impeller, a magnetic force acting in the direction of the first position acts on the at least one impeller.

12. A pump assembly according to claim 1, wherein the pump assembly is configured such that at least in the second position of the at least one impeller, a hydraulic force acting in the direction of the second axial position acts on a pressure-side, axial face side of the at least one impeller.

13. A pump assembly according to claim 12, wherein the pump assembly is configured such that in the second axial position of the at least one impeller, a suction-side axial face side of the at least one impeller or of a pressure element coupled to the at least one impeller is pressure-relieved.

14. A pump assembly according to claim 1, further comprising: at least one connection channel which connects a pressure region situated downstream of the at least one impeller to a side of the at least one impeller or of a pressure element coupled to the at least one impeller for transmitting a hydraulic pressure, said side being away from the pressure region; and a control element configured to control the flow through the connection channel and arranged in the connection channel.

15. A pump assembly according to claim 1, further comprising a structure defining a receiving space into which a closed, suction-side axial face side of the at least one impeller or a pressure element coupled to the at least one impeller enters in at least one position of the at least one impeller and which is configured such that, via a throttle location, the receiving space is subjected to a hydraulic pressure produced by the at least one impeller, for producing a hydraulic force, wherein an annular gap is defined between a peripheral edge of the structure and the closed, suction-side axial face side of the at least one impeller or the pressure element and the closed, suction-side axial face side of the at least one impeller or the pressure element is located at a position outside of the receiving space when the at least one impeller is in the first axial position, at least a portion of a control disc being located in the receiving space when the at least one impeller is in the second axial position, wherein the receiving space is in fluid communication with an inlet channel of the pump assembly when the at least one impeller is in the second axial position and when the at least one impeller is in the first axial position.

16. A pump assembly according to claim 1, wherein the at least one impeller comprises at least one exit opening and at least one entry opening, wherein the entry opening is situated in a peripheral section of the at least one impeller.

17. A pump assembly according to claim 16, wherein the entry opening is configured as an annular opening extending over a whole periphery of the at least one impeller.

18. A pump assembly according to claim 16, wherein the at least one impeller at a suction side comprises an extended cylindrical section which has an outer area which is 50 to 150% of an inner cross section in the inside of this section.

19. A heating installation comprising: a pump assembly comprising: an electric drive motor; at least one impeller driven by the electric drive motor, wherein: the at least one impeller is movable in an axial direction between at least one first axial position and a second axial position; the at least one impeller in the first axial position is situated in a first flow path through the pump assembly and delivers fluid through the first flow path; the at least one impeller in the second axial position is situated in a second flow path through the pump assembly and delivers a fluid through the second flow path; the at least one impeller is maintained in the at least one first axial position via a first acceleration; the at least one impeller is moved to the second axial position via a second acceleration; and the pump assembly is configured such that a movement of the at least one impeller between the first axial position and the second axial position at least in one direction is effected by a hydraulic force which acts on the at least one impeller and is produced by the delivered fluid; at least two installation parts, of which a first installation part is connected to the first flow path of the pump assembly, and a second installation part is connected to the second flow path of the pump assembly; and the pump assembly is configured such that the hydraulic force can be produced by differently accelerations of the drive motor.

20. A heating installation according to claim 19, wherein the at least two installation parts are at least two heat consumers or at least two heat sources.

21. A heating installation according to claim 19, wherein the first installation part is a heat exchanger for service water heating and the second installation part is a room heating circuit.

22. A heating installation according to claim 19, wherein the heating installation is configured such that a hydraulic pressure prevailing at a branching point between the first and the second installation part effects a hydraulic force in at least one of the positions of the at least one impeller which holds the at least one impeller in said at least one of the positions.

23. A heat installation according to claim 19, wherein the pump assembly further comprises a structure defining a receiving space, wherein a control disc is connected to the at least one impeller, wherein an annular gap is defined between a peripheral edge of the structure and the control disc and the control disc is located at a position outside of the receiving space when the at least one impeller is in the first axial position, at least a portion of the control disc being located in the receiving space when the at least one impeller is in the second axial position, wherein the receiving space is in fluid communication with an inlet channel of the pump assembly when the at least one impeller is in the second axial position and when the at least one impeller is in the first axial position.

24. A boiler comprising: a pump assembly comprising: an electric drive motor; at least one impeller driven by the electric drive motor, wherein: the at least one impeller is movable in an axial direction between at least one first axial position and a second axial position; the at least one impeller in the first axial position is situated in a first flow path through the pump assembly and delivers fluid through the first flow path; the at least one impeller is maintained in the at least one first axial position via a first acceleration of the electric drive motor; the at least one impeller is rotated in the at least one first axial position; the at least one impeller in the second axial position is situated in a second flow path through the pump assembly and delivers a fluid through the second flow path; the at least one impeller is moved to the second axial position via a second acceleration of the electric drive motor; the at least one impeller is rotated in the at second axial position; and the pump assembly is configured such that a movement of the at least one impeller between the first axial position and the second axial position at least in one direction is effected by a hydraulic force which acts on the at least one impeller and is produced by the delivered fluid; a primary heat exchanger; a secondary heat exchanger for service water heating as well as at least one connection for a room heating circuit, wherein the secondary heat exchanger and the connection for the room heating circuit are connected via a branching point to the primary heat exchanger, and a hydraulic pressure prevailing at the branching point, in at least one of the positions of the at least one impeller effects a hydraulic force which holds the at least one impeller in the at least one of the positions, wherein the pump assembly is configured such that the hydraulic force can be produced by differently accelerations of the drive motor.

25. A pump assembly according to claim 16, wherein the at least one impeller further comprises a closed, suction-side, axial face side, to which the peripheral section with the entry opening is adjacent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 is a schematic view of a pump assembly according to the invention with a connected heating installation, wherein the impeller of the pump assembly is located in a first position;

(3) FIG. 2 is a schematic view of a pump assembly according to the invention and according to FIG. 1, with which the impeller is located in a second position; and

(4) FIG. 3 is a schematic view of a pump assembly according to the invention, with a connected heating installation according to a second embodiment of the invention, wherein the impeller is located in the first position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) A pump assembly 2 is represented schematically in the FIGS. 1 and 2, and is integrated into a heating installation 4, for example a compact heating installation. The heating installation 4 comprises a first installation part which is formed by a room heating circuit 6. A second installation part or heating circuit is formed by a heat exchanger 8 for heating service water. The first heating circuit through the room heating circuit 6 and the heating circuit through the heat exchanger 8 branch at a branching point 10 which is situated downstream of a primary heat exchanger 12. The primary heat exchanger 12 can be arranged in a gas boiler or oil boiler for example and serves for heating the heating medium, in particular water, in the heating installation 4, and this water then flows downstream through the heat exchanger 8 for the service water heating, which forms a secondary heat exchanger 8 and/or the room heating circuit 6. Hereby, the fluid which forms the heating medium is delivered by the pump assembly 2 through the primary heat exchanger 12 and the heating circuits.

(6) The pump assembly 2 is a centrifugal pump assembly which comprises an electric drive motor 14 which via a shaft 16 drives an impeller 18 which is arranged on this in a rotationally fixed manner and in a manner fixed in the axial direction. The shaft 16 is preferably manufactured of ceramic and is machined to bearing quality over its complete length. The impeller is preferably manufactured of plastic. The drive motor 14 is designed as a wet-running electric motor which comprises a can 20 separating the stator 22 from the rotor space, in which the rotor 24 is arranged, in a fluid-tight manner. The rotor 24 is preferably designed as a permanent magnet rotor and likewise is fixed in an axially and rotationally fixed manner on the shaft 16. As the case may be, the rotor 24 could be designed as one piece with the shaft 16. The stator 22 which here is only shown schematically, can in the usual manner be formed of an iron part with stator coils arranged therein.

(7) The shaft 16 is axially displaceable with the rotor 24 and the impeller 18 in the axial direction X in its bearings 26. By way of this, the impeller 18 is movable between a first position which is shown in FIG. 1, and a second position which is shown in FIG. 2. In its first position which is shown in FIG. 1, the impeller 18 is situated closer to the stator 22 than in its second position which is shown in FIG. 2.

(8) The impeller 18 in the known manner comprises radially outwardly directed exit openings 28 which are open to a surrounding exit channel 30. The exit channel 30 in this example is connected to the entry side of the primary heat exchanger 12. I.e. the fluid exiting from the impeller 18 at the peripheral side is delivered through the exit channel 30 to the primary heat exchanger 12.

(9) Moreover, the impeller 18 at an axial face side which is opposite to the exit openings 28 comprises an axially directed suction port 32. The suction port 32 depending on the axial position of the impeller 18 is selectively in fluid-leading connection with a first inlet channel 34 or a second inlet channel 36. I.e. in the first position of the impeller 18 which is shown in FIG. 1 this sucks fluid via its suction port 32 out of the first inlet channel 34. This first inlet channel 34 connects downstream to the room heating circuit 6 and thus forms a part of a first flow path for the heating medium through this room heating circuit 6. If the impeller 18 is located in the first position shown in FIG. 1, the fluid is thus delivered by the impeller 18 through the exit channel 30, the primary heat exchanger 12 via the branching point 10 through the room heating circuit 6 for the service water heating and back into the first inlet channel 34 and from there into the suction port 32.

(10) If the impeller 18 is located in its axially displaced second position which is shown in FIG. 2, the suction port 32 to the second inlet channel 36 is opened, and this channel is connected to the exit side of the secondary heat exchanger 8 for the service water heating. In this position, with the drive of the impeller 18, fluid is delivered by the impeller 18 through the exit channel 30, the primary heat exchanger 12, via the branching point 10, through the secondary heat exchanger 8 and from there back into the second inlet channel 36, from which the suction port 32 sucks the fluid.

(11) A pressure element in the form of a control disc 38 is fastened on the shaft 16, in a manner axially distanced to the suction port 32. This control disc is distanced to the suction port 32 in the axial direction in a manner such that a peripheral gap 39 is formed between the control disc 38 and the peripheral edge of the suction port 32, and this gap in the first position lies opposite the first inlet channel 34 and in the second position of the impeller lies opposite the second inlet channel 36. In the first position which is shown in FIG. 1, the control disc 38 with a peripheral wall 37 closes the second inlet channel 36, so that in this position, essentially no fluid can flow out of the second inlet channel 36 into the suction port 32 and thus essentially no fluid or heating medium is delivered through the secondary heat exchanger 8 in the first position shown in FIG. 1. In the second position shown in FIG. 2, a peripheral wall of the impeller 16 closes the first inlet channel 34 so that the impeller 32 essentially sucks no fluid out of the first inlet channel 34 and thus essentially no fluid or heating medium is delivered through the room heating circuit 6. The peripheral wall of the impeller 18 and the control disc 38 thus simultaneously have the function of valve. elements.

(12) Thus a switch-over or change-over function between the room heating circuit 6 and the secondary heat exchanger 8 for service water heating and which is usually assumed by a 3/2 way valve in heating installations, can be achieved by the axial displacement of the impeller 16, and thus one can make do without such a valve. A simple branching at the branching point 10 is sufficient instead of such a valve. The construction of the heating installation is simplified in this manner.

(13) According to the invention, the axial displacement of the shaft 16 with the impeller 18 is achieved without additional actuation elements solely by way of the operating manner of the electric drive motor 14. The impeller 18 in the idle position of the pump assembly is located in the first position shown in FIG. 1, i.e. in its position which in this case is situated closest to the stator 22. In this example, this is achieved by magnetic restoring forces M in the electric drive motor 14 which acts in the axial direction X. As is to be seen in FIG. 1, the rotor 24 is centered in the axial direction with respect to the stator 22, i.e. the axial middle S of the stator is congruent with the axial middle R of the rotor. In the axially displaced position shown in FIG. 2, the rotor 24 is displaced with respect to the stator 22 in the axial direction X, by an amount a, which is necessary for displacing the impeller 18 into the shown second position. I.e. here the axial middle R of the rotor is axially displaced by the amount a with respect to the axial middle S of the stator. The rotor 24 designed as a permanent magnet rotor however on account of its permanent magnetic forces, tends to center itself with respect to the stator 22 in the axial direction. This effects an axial restoring force M, i.e. an axially acting magnetic force which pulls the rotor 24 as well as the shaft 16 with the impeller 18 into the first position shown in FIG. 1 and holds it in this idle position.

(14) If, departing from this idle position, the drive motor 14 is started up with a low acceleration, i.e. the speed in the temporal course is increased slowly, i.e. via a gentle gradient, this leads to a slow pressure build up in the exit channel 30 and in the flow paths which connect thereto downstream. Thereby, a pressure p.sub.1 prevails in the exit channel 30. A pressure p.sub.2 which is lower on account of the pressure loss in the primary heat exchanger 12 prevails at the branching point 10, downstream of the primary heat exchanger 12. Due to the pressure loss in the room heating circuit 6, the pressure in the heating circuit drops through the room heating circuit 6 in the further course, to the pressure p.sub.3 prevailing in the first inlet channel 34, wherein the pressure p.sub.3 forms the entry-side pressure at the impeller 18. Since essentially no fluid flow through the secondary heat exchanger 8 is effected in this condition, essentially the pressure p.sub.2 likewise builds up in this, so that with a slow pressure build-up finally the pressure p.sub.2 likewise prevails in the second inlet channel 36 as well as at the side 40 of the control disc 38 which is away from the impeller 18. This means a greater pressure p.sub.2 prevails at the suction-side, side 40 of the control disc 38 which is away from the impeller, than in the first inlet channel 34, i.e. than the suction-side pressure of the impeller 18. An additional hydraulic axial force F.sub.1 onto the control disc 38 is produced by way of this, and this force presses the control disc 38 together with the shaft 16 and the rotor 24 as well as the impeller 18 into the first position shown in FIG. 1 and holds it in this position. Simultaneously, a hydraulic force F.sub.2 acts on a pressure-side shroud 44 of the impeller 18 on operation of the pump assembly. Thereby, such an interaction can be achieved between the hydraulic forces F.sub.1 and F.sub.2 as well as the magnetic restoring force M, by way of adapting the geometry of the control disc 38 in relation to the area of the rear-side shroud 44 and the design of the drive motor 14, that the magnetic restoring force M and the hydraulic axial force F.sub.1 are greater than the hydraulic force F.sub.2. Thus, in this operating condition, i.e. when the impeller 18 rotates by way of drive of the drive motor 14, the occurring hydraulic force F.sub.1 pressing on the side 40 of the control disc 38 as well as the described magnetic restoring force M between the stator 22 and the rotor 24 keep the impeller 18 in this first position on operation. The impeller is maintained in the first axial position by a first acceleration.

(15) According to an alternative embodiment which is shown in FIG. 3, a seal 52 can be arranged between the pressure-side shroud 44 of the impeller 18 and an adjacent wall 50, and this seal prevents the pressure-side shroud 44 from being impinged by the pressure p.sub.1 prevailing in the exit channel 30. Thus, the previously described hydraulic force F.sub.2 is essentially eliminated, so that the impeller 18 can be held in the first position shown in the FIGS. 1 and 3 by the hydraulic force F.sub.1. This can be additionally supported by the magnetic restoring force M.

(16) The space in the inside of the seal 52 could moreover be subjected to a lower pressure from the inside of the impeller 18 via an optionally provided opening 54 which is drawn dashed in FIG. 3 and which is in the pressure-side shroud 44. Also several openings 54 could be provided instead of an opening 54. The preceding description as well as the subsequent description with regard to FIGS. 1 and 2 are referred to with respect to the further features of the second embodiment according to FIG. 3. Otherwise, the axial displacement of the impeller with the example shown in FIG. 3 is also effected in the manner explained previously and hereinafter.

(17) If, proceeding from a standstill, in which the rotor 18 is located in the position shown in FIG. 1, the electric drive motor 14 is greatly accelerated, i.e. the speed in a temporal course is increased rapidly with a steep gradient, this then leads to a rapid pressure build up in the first heating circuit through the room heating circuit 6. If this circuit has a lower flow resistance than the secondary heat exchange 8, which as a rule is the case in such heating installations, then with a rapid start-up, initially a lower pressure will still prevail in the second inlet channel 36 than in the first inlet channel 34.

(18) The control disc 38 is arranged such that with an axial displacement of the rotor 24 with the impeller 18, it immerses in the direction away from the drive motor 14 into a receiving space 43. The receiving space 43 in a plane transverse to the longitudinal or rotation axis X has a circular cross section whose inner diameter is slightly larger than the outer diameter of the control disc 38. Moreover, the receiving space 43 is designed in a pot-like manner and is only open at its side facing the impeller 18. In the first position of the impeller 18 which is shown in FIG. 1, the control disc 38 lies just outside the receiving space 43, so that the first side 40 of the control disc 38 which is away from the impeller, extends essentially in a plane with the peripheral edge at the axial end of the receiving space 43. Thus, an annular gap 45 is formed between this peripheral edge and the control disc 38. This gap forms a throttle for the fluid in the second inlet channel 36, so that a slower pressure built up is effected in the receiving space 43 than in the inlet channel 36. Thus, with a rapid start-up, a condition is achieved, in which firstly essentially no pressure is present at the first side 40 of the control disc 38 which is away from the impeller 18, whilst a pressure is built up at the opposite second side 42 of the control disc 38 which faces the impeller 18 and the suction port 32, and this pressure effects a force F.sub.3 in the axial direction, which is greater than the described magnetic restoring force M and thus moves the rotor 18 from the first position shown in FIG. 1 into the second position shown in FIG. 2. Additionally, the hydraulic force F.sub.2 acting on the pressure-side shroud 44 of the impeller 18 acts in the same direction as the hydraulic force F.sub.3. In this condition, essentially the same pressure p.sub.2 prevails in the first inlet channel 34 as at the branching point 10, since in this condition essentially no flow is effected anymore through the secondary heat exchanger 6. In contrast, the pressure through the room heating circuit 8 reduces so that then a lower pressure p.sub.3, i.e. the suction-side pressure of the pump assembly prevails in the second inlet channel 36. This pressure then also prevails at the side 40 of the control disc 38 which is away from the impeller 18, so that no forces acts on this disc, which would seek to axially move the shaft 16 with the impeller 18. Finally, in this condition the same pressures, specifically the pressure p.sub.3 then prevails at both sides 40 and 42 of the control disc 38. However, the pressure p.sub.1 acts on the pressure side of the impeller 18, i.e. on the pressure-side shroud 44 of the impeller 18, and this pressure in this operating condition holds the impeller 18 in the second position shown in FIG. 2 by way of the resulting hydraulic force F.sub.2, counter to the occurring magnetic restoring force M acting between the rotor 24 and the stator 22. The impeller is moved to the second axial position by a second acceleration.

(19) As a whole, a bistable system is created, in which in the first operating condition, in which the impeller 18 is located in the first position shown in FIG. 1, this is held in this first position in a stable manner by way of the prevailing magnetic and hydraulic forces. If however due to a rapid start-up of the motor, one succeeds right at the beginning in the impeller relocating into its second position shown in FIG. 2, here then a second stable condition is achieved, in which the impeller remains in this second position as long as the drive motor is driven. On stopping the drive motor, the rotor 24 is automatically moved back into the first position by way of the magnetic restoring force M which comes from the axial shift of the stator 22 and rotor 24.

(20) It is to be recognized that a switch-over between two flow paths can be achieved, specifically on the one hand between the flow path via the first inlet channel 34 and on the other hand the second flow via the second inlet channel 36, alone by way of the operating manner of the drive motor 14, specifically by way of the start-up behavior of the drive motor 14, without additional actuation elements or components being necessary for the axial displacement of the impeller 18.

(21) With the example shown here, this behavior results from the different flow resistances of the secondary heat exchanger 8 and of the heating circuit 6. It is to be understood that an equal effect could also be achieved by way of an additional connection channel 46 as is drawn in FIGS. 1 and 2 in a dashed manner as an option. The connection channel 46 runs out at the peripheral wall of the receiving space 23 in a region which in the second position is covered and thus closed by the peripheral wall 37 of the control disc 38. With a slow start-up of the drive motor 14, a rapid pressure build-up in the receiving space 43 is achieved via the connection channel 46, so that a hydraulic force F.sub.1 is built up very quickly there, which supports the magnetic force M, in order to hold the impeller 18 in the shown first position. In order to be able to succeed in a hydraulic force F.sub.3 acting on the second side 42 of the control disc 38 which is away from the impeller being built up, so as to displace the impeller 18 into the second position shown in FIG. 7, a control element 48 for the control of the flow through the connection channel 46 and which can be designed as a simple throttle or as a switchable valve is arranged in the connection channel 46.

(22) The connection channel 46 in particular is advantageous if the hydraulic resistance in the heating part upstream of the consumer, i.e. in particular in the primary heat exchanger 12 is very large. Thereby, the consumers form in this embodiment example the room heating circuit 6 and the secondary heat exchanger 8. If the hydraulic resistance in this heating part is very large, the pressure p.sub.2 at the branching point 10 is too small, in order to exert a suitable hydraulic force F.sub.1 on the impeller.

(23) If the control element 48 is designed as a switchable valve, then the connection channel 46 can be closed, so that no hydraulic pressure F.sub.1 can build up in the receiving space 43 and thus firstly a hydraulic force F.sub.3 is built up via the first inlet channel 34 and this acts on the second side 42 of the control disc 38. This hydraulic force F.sub.3 then leads to the axial displacement of the impeller 18 out of the position shown in FIG. 1 into the position shown in FIG. 2, wherein then additionally the control disc 38 with its peripheral wall 37 closes the connection channel 36. If the control element 48 is designed as a throttle, then by way of a suitable design of the throttle, one can ensure that with a rapid start-up of the drive motor from the first position shown in FIG. 1, a pressure p.sub.3 is built up more quickly in the first inlet channel 34 via the room heating circuit 6 than a pressure p.sub.2 in the receiving space 43 via the connection channel 46. Thus, the hydraulic force F.sub.3 which acts on the second side of the control disc 38 will rise more rapidly and lead to the desired axial displacement of the control disc 38 together with the shaft 16 and the impeller 18. Instead of providing a separate control element in the form of a throttle, the cross section of the connection channel 46 can also be dimensioned such that an identical effect is achieved.

(24) With the axial displacement of the control disc 38 from the first position shown in FIG. 1 into the second position shown in FIG. 2, with which the control disc 38 enters into the receiving space 43, the gap 45 at the outer periphery of the control disc 38 thereby effects a damping, since the fluid located in the receiving space 43 must exit out of the receiving space through this gap.

(25) Instead of switching over by way of different accelerations of the drive motor, such a switching-over could also be effected alone by way of the speed change of the drive motor 14, by way of a respective constructive design. If the impeller 18 for example were to be arranged such that the pressure-side shroud 44 were to bear on a seal and the pressure-side shroud 44 could be subjected to pressure in a targeted manner, then an axial displacement of the impeller 18 could also be achieved by way of this pressure impingement. The pressure impingement could for example be effected via a valve which opens given a certain pressure in the exit channel 30, said pressure being achieved on reaching a certain speed of the drive motor 14, in order to then subject the pressure-side shroud 44 to pressure.

(26) In the shown embodiment examples according to FIGS. 1 to 3, the control disc 38 could be an integral component of the impeller 18. Thus an impeller 18 is created, which has a closed, suction-side axial face side. This is formed by the control disc 38. The impeller then has a peripheral suction or entry opening which is formed by the gap 39. The gap 39 thereby preferably has an area which amounts to 50 to 150% of the cross-sectional area in the inside of the impeller 18 in the region of the gap 39. This inner cross-sectional area extends transversely to the longitudinal axis X. An adequately large flow cross section is ensured in this manner in the region of the gap 39. Moreover, one can recognize that such an impeller 18 in the region of the gap 39 has a cylindrical extension of a constant cross section which permits the axial displacement of the gap 39 between the inlet channels 34 and 36. The control disc 38 can be connected to the remaining parts of the impeller 18 via suitable webs or connection elements in the inside or however by way of the shaft 16 as is shown here.

(27) Moreover, a suitable speed regulation of the drive motor 14 can be effected, in order to hold the impeller in the described positions, in particular in the first position shown in FIGS. 1 and 3, wherein by way of this speed regulation, it is ensured that a certain flow or a certain delivery output is not exceeded, at which the hydraulic force F.sub.2 would rise to such an extent that an axial displacement of the impeller 18 would occur, which is not desirable in this situation.

(28) The described magnetic restoring force M could moreover be supported or also replaced by a spring force. Thus, for example, a compression spring could be arranged in the receiving space 43, which exerts a pressure force produced in the axial direction X, onto the axial face end of the shaft 16 and this force presses the Shaft 16 with the rotor 24 and the impeller 18 into the first position shown in FIGS. 1 and 3.

(29) Finally, the control disc 38 could also be designed as a stationary component, i.e. a component which does not rotate together with the shaft 16, and the shaft could come into sliding bearing contact on the control disc 38 merely at its face side. Thus, the control disc 38 despite this could yet exert an axial force which is directed in the direction of the hydraulic force F.sub.1, onto the shaft. By way of a suitable positive engagement, the control disc 38 could moreover also transmit a hydraulic force F.sub.3 onto the shaft 16 in the axial direction, without having to rotate together with this.

(30) Moreover, it is to be understood that more than just the two shown possible operating positions of the impeller 18 could also be realized. In particular, the impeller 18 can also assume intermediate positions as the case may be, by which means a mixed function could be realized. Thus, such a pump assembly could also function as a mixer, e.g. for a floor heating circuit. Then, for example, the first inlet channel 34 would be connected to the heating water feed, whilst the second inlet channel 36 is connected to the return from the floor heating circuit, and the exit channel 30 is connected to the entry side of the floor heating circuit. A mixed function could then be achieved by way of the axial displacement of the impeller 18, since more or less fluid is delivered out of the heating water feed depending on the position, and accordingly a lower or higher share of fluid is delivered out of the return of the floor heating circuit. Such a defined displacement of the impeller 18 also into intermediate positions can be effected by way of a speed change of the drive motor with the pressure change entailed by this, or by way of additional actuation elements. For example, the stator 22 could be displaced in the axial direction X, in order to move the axial centre S of the stator and thus simultaneously to accordingly co-displace the rotor 24, which as described above, seeks to centre itself in the stator 22 in the axial direction.

(31) Moreover, such a pump assembly, as has been previously described, instead of selectively serving two different heating circuits as installation parts of a heating installation, could also be used such that it selectively delivers fluid from two different heat sources or heat producers, for example a boiler heated by fossil fuel and a solar-thermal installation. In such a case, for example two different heat sources could be connected to the pump assembly 2 instead of the room heating circuit 6 and the secondary heat exchanger 8.

(32) While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.