EP2818726A1 - Centrifugal pump with axially shiftable impeller for feeding different fluid paths - Google Patents

Abstract

The invention relates to a pump unit (2) having an electric drive motor (14) and at least one impeller (18) driven by the latter, wherein the impeller (18) is movable in the axial direction (X) between at least a first and a second position, wherein the impeller (18) is located in its first axial position in a first flow path through the pump assembly (2) and conveys fluid through said first flow path, and the impeller (18) in its second position in a second flow path through the pump assembly (2 ) and a fluid through this second flow path, wherein the pump unit (2) is designed such that a movement of the impeller (18) between the first and the second position in at least one direction by one on the impeller (18) acting , is generated by the pumped fluid generated hydraulic force, and a heating system with such a pump unit.

Description

The invention relates to a pump unit with the features specified in the preamble of claim 1.

Out DE 101 15 989 A1 a centrifugal pump assembly is known in which a rotor shaft is axially displaceable together with the impeller, so that the impeller can be moved to a position in which its peripheral outlet openings are closed. In this way, the pump unit can take over a valve function and block a flow passage.

Out DE 30 02 210 A1 In addition, a pump unit with two wheels is known, which are driven by a common shaft. These wheels can be moved by axial movement of the shaft in each case between two Austrittskandlen in the axial direction, so that the wheels depending on the axial position of the shaft either water from a primary circuit in a secondary circuit and back or only separately promote in the primary circuit and the secondary circuit. For axial displacement of the shaft while a hydraulically or pneumatically actuated arranged outside the pump unit lifting device is provided. Such has the disadvantage that the shaft must be led out of the interior of the pump housing, so that a sealed passage must be provided.

It is an object of the invention to provide an improved pump unit and a heating system with such a pump unit, which allow a simple construction of the pump unit to promote a fluid through either at least two flow paths.

This object is achieved by a pump unit having the features specified in claim 1 and by a heating system with the features specified in claim 15. Preferred embodiments will become apparent from the subclaims, the following description and the accompanying figures.

The pump unit according to the invention has an electric drive motor, in particular a wet-running electric drive motor, d. H. a canned motor in which the stator is separated from the rotor space by a split tube. The pump unit is designed as a centrifugal pump unit and has at least one impeller, which is driven in rotation by the electric drive motor. For this purpose, the impeller can be connected via a shaft to the rotor of the electric drive motor. However, it is also possible that rotor and shaft form an integrated component and that the impeller is connected to this component. Also, the impeller may be integrally formed with the rotor and / or the shaft.

The impeller is arranged so that it can be moved in the axial direction between at least two positions, ie operating positions in which it can be rotationally driven by the drive motor. In this case, the pump unit is designed so that in a first of these two positions, the impeller is arranged so that it is located in a first flow path through the pump unit and promotes fluid during rotation through this first flow path. The second position or operating position is a position in which the Impeller in a second flow path, which runs through the pump unit, is located and during rotation, ie during operation of the pump unit, promotes fluid through this second flow path. That is, by axially moving the impeller along its rotational or longitudinal axis, it is possible to move the impeller between two operating positions, ie, said first position and said second position, to selectively provide fluid through a first or second flow path depending on the position in which the impeller is located. It is also conceivable that the impeller can assume one or more intermediate positions between said first and second positions in which it promotes fluid proportionally through both of the at least two flow paths.

The intended axial movement of the impeller is preferably chosen so large that in each position of the impeller, the cross-sectional area of the inlet opening of the impeller is so large that a certain maximum flow rate is not exceeded. Preferably, the pump unit is designed so that the inlet opening into the impeller, in particular a radial-side inlet opening in the impeller, as described below, has a surface which has in the range of 50 to 150% of the inner cross-sectional area of the impeller on the suction side. This inner cross-sectional area extends transversely to the longitudinal or rotational axis of the impeller.

According to the invention, the pump unit is designed in such a way that, at least in one direction of movement of the impeller, this movement takes place by means of a hydraulic force which itself is caused by the fluid conveyed by the impeller. Ie. the pump unit is designed so that the pressure of the fluid conveyed by the impeller acts on a suitable surface such that an axial direction, ie parallel to the axis of rotation of the Impeller directed hydraulic force is generated, which is used to move the impeller axially in this direction. The use of the hydraulic force to move the impeller has the advantage that can be dispensed with external actuators and the force required to move rather by the pump unit, that can be generated by the rotating impeller itself. This has the particular advantage that it is not necessary to guide the shaft or the rotor out of the sealed interior of the pump assembly to be coupled there with an actuator for axial displacement. Preferably, as in conventional canned motors, the entire rotor may be tightly encapsulated inside the can.

In addition, the pump unit is preferably designed so that the impeller in operation, d. H. when rotationally driven by the drive motor, by at least one hydraulic force generated by the conveyed fluid in at least one of the positions, i. H. in the first or second position. For this purpose, the fluid pressure generated by the impeller can act on a corresponding connected to the impeller or coupled to the power transmission pressure surface, so that a force is exerted on the pressure surface, which presses the impeller in the desired position or holds in this position. The force is preferably directed parallel to the axis of rotation of the impeller. Ie. said pressure surface preferably has an orientation transverse to this axis of rotation or at least one component directed transversely to the axis of rotation.

Further preferably, the pump unit is designed so that the impeller in operation by an interaction of at least one of the funded fluid generated hydraulic force, a spring force and / or an axially acting magnetic force in at least one of the positions, ie said first or second position, held is, wherein the magnetic force further preferably acts on a rotor connected to the impeller of the drive motor. Particularly preferably, the impeller is held by the magnetic force in one of the two said positions, wherein in this state, the magnetic force is greater than an acting in the opposite direction of the impeller hydraulic force. Alternatively or additionally, to the magnetic force, a spring force generated by a spring element act on the impeller so that it is held in one of the positions. In the second position then acts on the impeller, a hydraulic force, for example in a manner described in the above-oriented pressure surface, which is greater than the magnetic force and / or the spring force, so that the impeller against the magnetic force and / or the spring force in the second position is held. Ie. the impeller may be selectively held in the first or second position by interaction of a magnetic force and / or a spring force and a hydraulic force, wherein in one of the positions the hydraulic force and in the other position the magnetic force or spring force is greater. In order to achieve a switching between the positions, one of the forces must be correspondingly increased and / or the other force must be reduced accordingly. Since the hydraulic force is preferably generated by the impeller itself during its rotation, this force will not act at standstill of the pump unit, so that in this state then preferably only a magnetic force and / or a spring force acts on the impeller. In this way, the impeller can be moved in the idle state by the magnetic force and / or the spring force in a predetermined one of the two positions, so that the impeller is always in a defined one of the two possible positions at rest of the pump unit. Ie. When starting, the pump set always starts from a defined position.

According to a further preferred embodiment, the pump unit can also be designed such that by the energization of the drive motor, an axially acting magnetic force is generated, which can be generated for example by interaction between the rotor and the stator of the drive motor. Such a magnetic force can also move the impeller from a rest position, which represents a first position, in the axial direction to a second position. In the first position, the impeller can then be held, for example, by a magnetic force and / or a spring force. Such occurring during operation of the drive motor magnetic axial force can optionally be supported with a suitable embodiment of the pump unit by the above-described hydraulic axial force which is generated by the impeller itself.

The impeller is preferably connected to a rotor of the electric drive motor and at least one magnetic force, in particular the magnetic force described above, which acts on the impeller in the axial direction, preferably results from a magnetic interaction between the rotor and a surrounding stator, in particular one axial offset between rotor and stator. For example, when the rotor is formed as a permanent magnet rotor and located in a stator having iron elements and coils, the rotor tends to magnetically center in the axial direction inside the iron part of the stator. If the rotor is moved out of this centered position in the axial direction, this results in an axial magnetic restoring force acting against this movement. This can be used as a magnetic force in the axial direction for moving the rotor and an associated impeller between the two said positions and / or for holding the impeller in one of these positions. Thus, the pump unit can be designed so that when operating the pump the impeller in the axial direction, a pressure of the pumped fluid at least in certain operating states acts such that a hydraulic force is generated on the impeller, which moves the impeller with the rotor in the axial direction against the resulting magnetic restoring force from the centered position in the stator. When the hydraulic force is removed again, the rotor with the impeller is again moved back into its initial position in the axial direction by said magnetic restoring force. Ie. Here, a magnetic actuating and / or holding force, which acts on the rotor and thus the impeller in the axial direction can be generated without additional magnetic elements or other holding or actuating elements would be required in the pump unit. Instead of the described magnetic restoring force, a spring force generated by a spring element can be used to hold the impeller in a desired position. The pump unit could also be designed so that a spring force and a magnetic force in the manner described above hold the impeller in one of the positions.

More preferably, the pump unit is designed so that the impeller is arranged in its first position such that it promotes in a first outlet channel and the impeller is arranged in its second position such that it conveys into a second outlet channel. Ie. the impeller, when moved between the first and second positions, is moved between the two said exit edges, preferably remaining in communication with one and the same inlet channel in both positions. Ie. Here, the switching between two flow paths takes place in that the output, in which promotes the impeller, is changed by axial movement of the impeller.

Conversely or additionally, according to another possible embodiment of the invention, it is possible that the impeller is arranged in its first position such that it is connected at its suction side with a first inlet channel, and the impeller is arranged in its second position such that it is connected at its suction side with a second inlet channel. According to a preferred embodiment, the impeller remains in both positions in fluid-conducting connection with the same outlet channel. Ie. the impeller conveys into the same outlet passage in both positions but sucks in the first position through a different entrance passage than in the second position. In this way, in this embodiment, a switching between the two flow paths is achieved in that the impeller is brought into fluid communication with two different inlet channels.

It is understood that both embodiments can be combined with each other, d. H. upon movement of the impeller both the connection to the inlet channel and the connection to the outlet channel can be changed. For example, it is possible to switch the subsidy between two separate circuits.

According to a particularly preferred embodiment of the invention, the pump unit is designed such that the hydraulic force can be generated by a specific operating mode of the drive motor, in particular by a speed change. For example, by increasing the speed of the output side pressure of the fluid can be increased so that the pressure acting on the above-mentioned pressure surface increased so much that a counteracting force, in particular the magnetic force described above, is overcome and then the impeller in another Position is shifted in the axial direction. Thus, by changing the speed of the pump unit, the conveying path through the pump unit can be changed by due to the changing fluid pressures, the impeller moves axially. Also, a valve could be opened by speed and pressure increase, whereby a pressure surface is acted upon by the hydraulic pressure.

According to a further possible embodiment, the pump unit may be designed such that the hydraulic force, by which the impeller is axially displaced, is generated by different degrees of acceleration of the drive motor. Different strong accelerations of the drive motor can lead to different pressure build-up in the subsequent to the pump unit line systems, so that on the impeller itself or with the impeller, for example via the rotor shaft connected or force-transmitting coupled pressure surfaces, different pressures can act. For example, two opposing pressure surfaces, for. B. on opposite axial sides of the impeller, may be provided, which are both acted upon by the impeller generated by the fluid pressure, but via a subsequent conduit system. Depending on which of the two pressure surfaces at first a higher pressure builds up, then the impeller can be moved by the higher hydraulic force in the appropriate direction. By appropriate design of the pump unit can then be prevented that on the other side of the displacement counteracting force is generated. This can be done, for example, by closing a flow path or by counteracting an interaction or assistance by a magnetic force as described above.

When the switching between the two flow paths is achieved by shifting the impeller by various operating states of the drive motor, these operating conditions become the flow paths Preferably assigned so that in the event that one of the operating conditions should offer a poorer efficiency, this operating state is assigned to that flow path, which is used less frequently. This could be, for example, the flow path through which the heating medium is passed into a heat exchanger for domestic water heating, since heating systems usually require less heating of the domestic water than the heating of connected heating circuits.

Particularly preferably, the pump unit is designed as a bistable system, in which the impeller in operation by the acting hydraulic and / or magnetic forces and / or spring forces, in particular by those as described above, each held stable in its first and second positions becomes. This means that once the impeller has reached one of the two positions during operation, it remains in this position during operation. To move to the other position is either an external force to apply or to change the operating state of the pump unit so that a switching force is generated, which shifts the impeller in the respective other position. Particularly preferably, the pump unit can be designed so that it can cause a movement of the impeller from one to the other position only when starting, ie when accelerating the drive motor from a standstill. Thus, as described above, the pump unit may be configured so that the idle wheel is held in one of the positions by a magnetic force and / or a spring force. Furthermore, the pump unit can be designed so that due to the flow resistance of the subsequent piping systems or hydraulic components, a pressure acting on a pressure surface, which is used to generate power in the axial direction, pressure builds up at different rates. Now if there are two opposite pressure surfaces and both with the same hydraulic Force are applied, there is no force which acts in the axial direction of the impeller and this could move, for example, against a magnetic force or spring force. However, if, for example, by particularly fast acceleration of the impeller at one of the pressure surfaces faster pressure builds up than at the other, creates a resulting axial force, which can be used to move the impeller in the other position. In the aforementioned bistable structure, the impeller then remains in operation in this position. This can be achieved, for example, by a valve function of an element moving with the impeller, by which it is prevented that the opposite pressure surface is pressurized.

Preferably, the impeller is located in its first position axially closer to the stator of the drive motor than in its second position. Ie. it is moved from its first position in the axial direction away from the stator to the second position.

More preferably, the pump unit is configured so that in the first position of the impeller acting in the direction of the first position hydraulic force on a suction side axial end side of the impeller or a pressure element or a pressure surface, which is coupled to transmit force to the impeller acts. Ie. the hydraulic force in the first position causes the impeller to be pushed to the first position. The fluid pressure acts on the said axial end face of the impeller or a pressure element.

In addition, the pump unit may preferably be designed such that in the first position of the impeller acts in the direction of the first position magnetic force and / or spring force on the impeller. This may, for example, be a magnetic force which, as described above, consists of an axial offset between Rotor and stator results, ie when the rotor with the impeller is moved out of this position, creates a magnetic restoring force between the rotor and stator, which pushes or pulls the rotor in the first position. Alternatively or additionally, a spring element for generating a spring force could be present. Such a magnetic force and / or spring force can serve, in particular, to hold the impeller in the first position when the pump unit is stationary, so that the impeller always starts from the first position.

According to a further preferred embodiment, the pump unit is designed such that at least in the second position of the impeller acting in the direction of the second position hydraulic force on a pressure side axial end side of the impeller or a second position facing away from a pressure element or one of the second position facing away pressure surface acts, which is coupled with the impeller force-transmitting. This hydraulic force can then be used to hold in operation the impeller in the second position, in particular against a magnetic force and / or spring force, as described above.

Furthermore, it is preferred that the pump unit is designed such that in the second position of the impeller, a suction-side axial end face of the impeller or the end face of a coupled to the impeller pressure element is depressurized. The axial end face of the impeller on the suction side is pressure-relieved, in particular, when the low output pressure of the fluid flowing back into the circuit to the pump unit is present here. The pressure reduction or pressure loss can occur, for example, in a downstream of the pump unit downstream piping system. Particularly preferably, the line systems connected to the flow paths have different throttle properties, so that when starting the Impeller of the pressure build-up in these systems runs at different speeds, so that the axial displacement of the impeller can be achieved by different strong accelerations. With slow acceleration, a more uniform pressure build-up in both flow paths can be achieved, while with strong acceleration, a rapid pressure build-up is achieved, in particular in the flow path with the lower throttle effect. Instead of using here the return flow through the flow paths for controlling the hydraulic forces, it is also possible to provide in the pump unit one or more corresponding control lines with optionally throttle elements.

Thus, preferably at least one connecting channel may be present in the pump unit, which connects a downstream of the impeller pressure range or pressure channel with a side facing away from the pressure area of the impeller or a coupled to the impeller for power transmission pressure element to a hydraulic pressure from the output side of the impeller to transmit to the side facing away from the printing area of the impeller or the pressure element. Thus, a hydraulic force can be generated, which presses the impeller in one of the positions, in particular the first position, or holds in this. Preferably, in the connecting channel, a control element, for example a switchable valve or a throttle point, be arranged to control the flow through the connecting channel. By such an element, the pressure build-up on the connected side of the impeller or the pressure element can be prevented or delayed to prevent the axial displacement of the impeller and, for example, to move the impeller to the second position by pressing on the opposite side of the impeller or the pressure element is first built up a higher pressure.

Further, it is preferred that a receiving space is present, in which a closed suction-side axial end face of the impeller or a pressure element coupled to the impeller, such as a control disk, enters at least one position of the impeller and which is designed such that it preferably via a Throttle is acted upon by a hydraulic pressure generated by the impeller for generating a hydraulic force. The throttle point can be formed by a gap between a peripheral wall of the receiving space and the outer periphery of the axial end face of the impeller or the pressure element. In addition, a damping effect on entry of the end face or of the pressure element into the receiving space can be achieved via this gap or throttle point. By the hydraulic pressure, which is passed into the receiving space and the adjacent closed end face of the impeller or the end face of a coupled to the impeller pressure element applied, the impeller can be pressed into a receiving space facing away from the position and optionally held in this.

The invention is in addition to the pump unit described above, a heating system with such a pump unit. Ie. the pump unit acts in the heating system, which in the sense of this invention, an air conditioner is to be understood as heating circulation pump unit to circulate the heat carrier in the heating system, in particular water. The heating system according to the invention has at least two system parts, of which a first part of the system is connected to the first flow path of the pump unit and the second part of the system to the second flow path of the pump unit. The system parts may be heat exchangers and piping systems, which in each case form a circuit with the flow paths of the pump unit. Ie. the first flow path of the pump unit lies in a fluid circuit through the first part of the plant and the second flow path of the pump unit is in a fluid circuit through the second part of the system, so that the impeller in its first position promotes fluid through the first part of the system and in its second position fluid through the second part of the system. Thus, by displacing the impeller from the first to the second position different plant parts of a heating system can be supplied with heating or cooling medium.

Preferably, the two parts of the system are at least two consumers or at least two heat sources. For example, two consumers can be two different heating circuits of a heating system which heat different parts of the building. As a different heat sources, for example, a conventional, heated with fossil fuels boiler and a solar thermal system can serve. The two flow paths through the pump unit are then each connected to one of the heat sources or a consumer via corresponding piping systems, so that the heating medium or fluid, especially water is conveyed through these equipment parts, depending on whether the impeller in the first or the second position located.

Particularly preferably, the first part of the plant is a space heating circuit and the second part of the plant is a heat exchanger for domestic water heating. Such a configuration can be found, for example, in compact heating systems, which are used for heating homes and, for example, single-family homes. In these, a heat generator in the form of a fossil-heated boiler is usually provided, which has a primary heat exchanger in which a heating medium, in particular water, is heated. This is then optionally by the radiator in the rooms to be heated, ie by a space heating circuit, or by a heat exchanger for Warming of service water. For this purpose, a circulation pump is usually provided and the switching between the space heating circuit and the heat exchanger for domestic water heating is effected by a 3/2-way valve. If the circulation pump is replaced by a pump unit, as described above, can be dispensed with in such a system on the 3/2-way valve, since the switching between domestic water heating and space heating can then be done by axial displacement of the impeller in the pump unit. Thus, when it is in its first position, the impeller conveys through the first flow path in the pump unit and thus through a connected first part of the installation, namely the space heating circuit. When the impeller is in its second position, it promotes the heating medium through the second flow path and thus through the connected to this heat exchanger for domestic water heating. Thus, the construction of a heating system can be significantly simplified as can be dispensed with an additional valve and the switching between the heating circuits ideally can be done solely by targeted control of the drive motor of the pump unit, for example by changing the speed or change the acceleration when starting.

More preferably, the heating system is configured such that at a branch point between the first and second abutment part prevailing hydraulic pressure in at least one of the positions of the impeller causes a hydraulic force that holds the impeller in this position. In this case, the plant is preferably designed so that this hydraulic pressure is transmitted through that part of the plant through which no flow takes place in this position of the impeller. Thus, essentially the unused plant part can be used as a control line for controlling or holding pressurization of the impeller. Ie. Here, the prevailing at the branch point Pressure used to hold the impeller in one of its positions or move it to the desired position.

The invention further relates to a boiler for a heating system, as described above. The boiler preferably has a pump unit as described above. Further, it has a primary heat exchanger in which the heating fluid is heated, for example by a burner for fossil fuels, preferably gas. Furthermore, it is provided with a secondary heat exchanger for domestic water heating and at least one connection for a space heating circuit. This connection for the space heating circuit has at least one connection for the trace and a connection for the return of the space heating circuit. The secondary heat exchanger and the connection for the space heating circuit, d. H. in particular its trace, are connected via a branch point with the primary heat exchanger. Ie. downstream of the primary heat exchanger branches at the branch point of the circuit to the connection for the space heating circuit and to the secondary heat exchanger. The boiler is designed so that at the branch point prevailing hydraulic pressure in at least one of the positions of the impeller of the pump unit in this causes a hydraulic force which holds the impeller in this position. Thus, as described above with reference to the heating system, the hydraulic pressure at the branch point is used to control or hold the impeller in a desired position.

The invention is also an impeller for a centrifugal pump unit beyond. 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. essential to the invention Feature is that the inlet opening is not located on the axial side but in a peripheral portion of the impeller, that is, 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, to change or switch by axial displacement between two possible flow paths or to cause a mixing function.

Particularly preferably, this impeller according to the invention has a closed suction-side axial end face, on which the peripheral section adjoins the inlet opening. Ie. the fluid to be delivered flows essentially not in the axial direction but 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, ie 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 axial inlet opening and an additional element, namely the disc, an inventive impeller created be, which has an open to the outer periphery of the inlet opening.

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, in the opening optionally webs may be formed in the axial direction, which interconnect the peripheral edges which define the opening, in order 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, the inlet portion or inlet opening being sufficiently sealed to the outside in each position of the impeller can be used to separate the pressure and the suction side of the impeller in each position from each other.

Fig. 1

schematisch ein erfindungsgemäßes Pumpenaggregat mit einer angeschlossenen Heizungsanlage, wobei sich das Laufrad des Pumpenaggregates in einer ersten Position befindet,

Fig. 2

schematisch ein erfindungsgemäßes Pumpenaggregat gemäß Fig. 1, bei welchem sich das Laufrad in einer zweiten Position befindet und

Fig. 3

schematisch ein erfindungsgemäßes Pumpenaggregat mit einer angeschlossenen Heizungsanlage gemäß einer zweiten Ausführungsform der Erfindung, wobei sich das Laufrad in einer ersten Position befindet.

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

Fig. 1

1 schematically a pump unit according to the invention with a connected heating system, wherein the impeller of the pump unit is in a first position,

Fig. 2

schematically a pump unit according to the invention according to Fig. 1 in which the impeller is in a second position and

Fig. 3

schematically an inventive pump unit with a connected heating system according to a second embodiment of the invention, wherein the impeller is in a first position.

In the FIGS. 1 and 2 schematically a pump unit 2 is shown, which is integrated in a heating system 4, for example, a compact heating system. The heating system 4 has a first part of the plant, which is formed by a space heating circuit 6. A second system part or heating circuit is formed by a heat exchanger 8 for heating domestic water. The first heating circuit through the space heating circuit 6 and the heating circuit through the heat exchanger 8 branch at a branch point 10 which is located downstream of a primary heat exchanger 12. The primary heat exchanger 12 may be arranged for example in a gas or oil boiler and is used to heat the heating medium, in particular water, in the heating system 4, which downstream then through the heat exchanger 8 for the domestic water heating, which forms a secondary heat exchanger 8, and / or the space heating circuit 6 flows. In this case, the fluid which forms the heating medium, promoted by the pump unit 2 through the primary heat exchanger 12 and the heating circuits.

The pump unit 2 is a centrifugal pump unit, which has an electric drive motor 14, which via a shaft 16 drives a rotationally fixed on this and fixed in the axial direction impeller 18. The shaft 16 is preferably made of ceramic and processed over its entire length in bearing quality. The impeller is preferably made of plastic. The drive motor 14 is designed as a wet-running electric motor, which has a can 20, which fluid-tightly separates the stator 22 from the rotor space in which the rotor 24 is arranged. The rotor 24 is preferably designed as a permanent magnet rotor and also fixed axially fixed and rotationally fixed to the shaft 16. Possibly. For example, the rotor 24 could be integrally formed with the shaft 16. The stator 22, which is shown here only schematically, can usually be formed from an iron part with stator coils arranged therein.

The shaft 16 is axially displaceable with the rotor 24 and the impeller 18 in the axial direction X in their bearings 26. Thereby, the impeller 18 is between a first position, which in Fig. 1 is shown, and a second position, which in Fig. 2 shown is movable. In his first position, which in Fig. 1 is shown, the impeller 18 is located closer to the stator 22 than in its second position, which in Fig. 2 is shown.

The impeller 18 has in a known manner radially outwardly directed outlet openings 28, which are open to a surrounding outlet channel 30 out. The outlet channel 30 is in this example with the Entrance side of the primary heat exchanger 12 connected. Ie. the fluid exiting from the impeller 18 is conveyed through the outlet channel 30 to the primary heat exchanger 12.

Further, the impeller 18 at an outlet openings 28 opposite axial end face on an axially directed suction port 32. Depending on the axial position of the impeller 18, the suction port 32 is optionally in fluid communication with a first inlet channel 34 or a second inlet channel 36. Ie. in the first in Fig. 1 shown position of the impeller 18 sucks this via its suction port 32 fluid from the first inlet channel 34 at. This first inlet channel 34 connects downstream to the space heating circuit 6 and thus forms part of a first flow path for the heating medium through this space heating circuit 6. When the impeller 18 in the in Fig. 1 The fluid is thus conveyed from the impeller 18 through the outlet channel 30, the primary heat exchanger 12 via the branch point 10 through the space heating circuit 6 for domestic water heating and back into the first inlet channel 34 and from there into the suction port 32.

When the impeller 18 is in its axially displaced second position, which in Fig. 2 is shown, the suction port 32 is opened to the second inlet channel 36 which is connected to the output side of the secondary heat exchanger 8 for the domestic water heating. In this position, when driving the impeller 18 fluid from the impeller 18 through the outlet channel 30, the primary heat exchanger 12, via the branch point 10, through the secondary heat exchanger 8 and from there back into the second inlet channel 36, from which the suction port 32, the fluid sucks.

Axially spaced from the suction port 32 is attached to the shaft 16, a pressure element in the form of a control disk 38. This is so of the suction port 32 in the axial direction spaced, that between the control disk 38 and the peripheral edge of the suction mouth 32, a circumferential gap 39 is formed, which in the first position, the first inlet channel 34 and in the second position of the impeller opposite the second inlet channel 36. In the first position, which in Fig. 1 is shown, the control disc 38 closes with a peripheral wall 37, the second inlet channel 36, so that in this position substantially no fluid from the second inlet channel 36 can flow into the suction port 32 and so in the first in Fig. 1 shown position substantially no fluid or heating medium is conveyed through the secondary heat exchanger 8. In the in Fig. 2 a peripheral wall of the impeller 16 closes the first inlet channel 34, so that the impeller 32 substantially no fluid from the first inlet channel 34 sucks and thus substantially no fluid or heating medium is conveyed through the space heating circuit 6. The peripheral wall of the impeller 18 and the control disk 38 thus simultaneously have the function of valve elements.

Thus, by the axial displacement of the impeller 16, a switching function between the space heating circuit 6 and the secondary heat exchanger 8 for domestic water heating can be achieved, which is usually taken over in heating systems of a 3/2-way valve, which can thus be dispensed with. Instead of such a valve, a simple branching at the branch point 10 is sufficient. In this way, the construction of the heating system is simplified.

According to the invention, the axial displacement of the shaft 16 is achieved with the impeller 18 without additional actuators alone by the operation of the electric drive motor 14. In the rest position of the pump unit is the impeller 18 in the in Fig. 1 shown first position, ie in his case closest to this Stator 22 located position. In this example, this is achieved by magnetic restoring forces M in the electric drive motor 14, which act in the axial direction X. As in Fig. 1 can be seen, the rotor 24 is centered relative to the stator 22 in the axial direction, ie, the axial center S of the stator is congruent with the axial center R of the rotor. In the in Fig. 2 shown axially displaced position of the rotor 24 relative to the stator 22 in the axial direction X by a dimension a, which is required for moving the impeller 18 in the second position shown, moved. Ie. Here, the axial center R of the rotor is axially offset by the dimension a with respect to the axial center S of the stator. The designed as a permanent magnet rotor rotor 24, however, strives to center in the axial direction relative to the stator 22 due to its permanent magnetic forces. This causes an axial restoring force M, ie an axially acting magnetic force, which the rotor 24 and the shaft 16 with the impeller 18 in the in Fig. 1 shown pulled first position and holds in this in rest position.

If starting from this rest position of the drive motor 14 is approached with a low acceleration, ie, the speed over time, that is, a flat ramp, increased, this leads to a slow pressure build-up in the outlet channel 30 and the downstream there flow paths. In this case, there is a pressure p ₁ in the outlet channel 30. Downstream of the primary heat exchanger 12 prevails at the branch point 10 due to the pressure loss in the primary heat exchanger 12 lower pressure p. ₂ Due to the pressure loss in the space heating circuit 6, the pressure in the heating circuit drops through the space heating circuit 6 in the further course to the pressure prevailing in the first inlet channel 34 pressure p ₃ , wherein the pressure p _{3 forms} the input side pressure on the impeller 18. Since in this state essentially no fluid flow takes place through the secondary heat exchanger 8, the pressure p ₂ builds up essentially in this state as well, so that at slow pressure build-up, finally in the second inlet channel 36 and on the side facing away from the impeller 18 40 of the control disk 38, the pressure p _{2 also} prevails. This means on the suction-side, the impeller side facing away from the control disk 38, a higher pressure p ₂ prevails as in the first inlet channel 34, ie as the suction-side pressure of the impeller 18. This creates an additional hydraulic axial force F ₁ on the control disk 38, which the control disk 38 together with the shaft 16 and the rotor 24 and the impeller 18 in the in Fig. 1 shown first position and holds in this holds. At the same time, a hydraulic force F ₂ acts on a pressure-side pressure disk 44 of the impeller 18 during operation of the pump assembly. By adjusting the size of the control writing 38 in relation to the surface of the rear cover plate 44 and the design of the drive motor 14 can be achieved between the hydraulic forces F ₁ and F ₂ and the magnetic restoring force M, such an interaction that the magnetic restoring force M and hydraulic axial force F _{1 are} greater than the hydraulic force F ₂ . Thus, in this operating state, ie when the impeller 18 rotates by driving the drive motor 14, the occurring hydraulic force F ₁ , which presses on the side 40 of the control disk 38, and the described magnetic restoring force M between the stator 22 and rotor 24, the impeller 18th in operation in this first position.

According to an alternative embodiment, which in Fig. 3 is shown, between the pressure-side cover plate 44 of the impeller 18 and an adjacent wall 50, a seal 52 may be arranged, which prevents the pressure-side cover plate 44 is acted upon by the pressure prevailing in the outlet passage 30 p ₁ . Thus, substantially eliminates the previously described hydraulic force F ₂ , so that the impeller 18 by the hydraulic force F ₁ in the in FIGS. 1 and 3 shown first position can be held. This can be additionally supported by the magnetic restoring force M. The space in the interior of the seal 52 could also be provided with a lower pressure from inside the impeller 18 via an optional, in Fig. 3 dashed line aperture 54 in the pressure-side cover plate 44 are acted upon. Instead of an opening 54, a plurality of apertures 54 could also be provided. With respect to the further features of the second embodiment according to Fig. 3 is to the preceding description and the following description with reference to the FIGS. 1 and 2 directed. Incidentally, the axial displacement of the impeller also takes place in the Fig. 3 Example shown in the foregoing and explained below manner.

When starting from standstill, in which the rotor 18 in the in Fig. 1 shown position, the electric drive motor 14 is greatly accelerated, ie, the speed is increased over time with a steep ramp, this leads to a rapid pressure build-up in the first heating circuit through the space heating circuit 6. If this circuit has a lower flow resistance than the secondary heat exchanger 8, which is usually the case in such heating systems, a lower pressure will initially prevail in the second inlet channel 36 at a rapid start than in the first inlet channel 34.

The control disk 38 is arranged so that it dips in the direction away from the drive motor 14 with axial displacement of the rotor 24 with the impeller 18 in a receiving space 43. The receiving space 43 has in a plane transverse to the longitudinal or rotational axis X has a circular cross-section whose inner diameter is slightly larger than the outer diameter of the control disk 38. Furthermore, the receiving space 43 is cup-shaped and open only on its side facing the impeller 18 side. In the in Fig. 1 shown first position of the impeller 18, the control disk 38 is just outside the receiving space 43, so that the first side 40 of the control disk 38, which faces away from the impeller, extends substantially 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 disk 38. This forms a throttle for the fluid in the second inlet channel 36, so that in the receiving space 43, a slower pressure build-up than in the inlet channel 36 takes place. Thus, a state is reached at fast start, in which at the first first side facing away from the impeller 18 of the control disk 38 initially substantially no pressure, while at the opposite the impeller 18 and the suction mouth 32 facing the second side 42 of the control disk 38 itself builds up a pressure which causes a force F ₃ in the axial direction, which is greater than the described magnetic restoring force M and thus the rotor 18 from the in Fig. 1 shown first position in the in Fig. 2 moved shown second position. In addition, acts in the same direction as the hydraulic force F _3, the hydraulic force F ₂ , which acts on the pressure-side cover plate 44 of the impeller 18. In this state, substantially the same pressure p ₂ then prevails in the first inlet channel 34 as at the branch point 10, since in this state substantially no flow takes place through the secondary heat exchanger 6. By the space heating circuit 8, however, the pressure is reduced, so then in the second inlet channel 36, a lower pressure p ₃ , ie, the suction-side pressure of the pump unit, prevails. This pressure then prevails also on the side facing away from the impeller 18 40 of the control disk 38, so that no forces act on this, which would endeavor to move the shaft 16 with the impeller 18 axially. Finally, prevail in this state then on both sides 40 and 42 of the control disk 38, the same pressures, namely the pressure p _3rd However, acting on the pressure side of the impeller 18, ie on the pressure-side cover plate 44 of the impeller 18 of the pressure p ₁ , which the impeller 18 in this operating condition by the resulting hydraulic force F _2nd against the occurring magnetic restoring force M, which acts between the rotor 24 and stator 22, in the Fig. 2 holds shown second position.

Overall, such a bistable system is provided in which in the first operating state in which the impeller 18 in the in Fig. 1 shown first position, this is held by the prevailing magnetic and hydraulic forces stable in this first position. However, it is achieved by rapid startup of the drive motor that the impeller shifts to the beginning in its second position, which in Fig. 2 is shown here, a second stable state is reached, in which the impeller then, as long as the drive motor is driven, remains in this second position. When stopping the drive motor, the rotor 24 is automatically moved back to the first position by the magnetic restoring force M, which results from the axial offset of the stator 22 and rotor 24.

It can be seen that thus switching between the two flow paths, namely once the flow path via the first inlet channel 34 and once the second flow path via the second inlet channel 36, alone by the operation of the drive motor, namely by the starting behavior of the drive motor 14, achieved can be without additional actuators or components for axial displacement of the impeller 18 would be required.

In the example shown here, this behavior results from the different flow resistances of the secondary heat exchanger 8 and the space heating circuit 6. It is to be understood that a same effect could also be achieved by an additional connection channel 46, as he in FIGS. 1 and 2 dashed line is shown as an option. The connecting channel 46 opens at the peripheral wall of the receiving space 23 in a region which in the second Position of the peripheral wall 37 of the control disk 38 is covered and thus closed. Via the connecting channel 46, a rapid build-up of pressure in the receiving space 43 is achieved during slow starting of the drive motor 14, so that there quickly a hydraulic force F _{1 is} built up, which supports the magnetic force M to hold the impeller 18 in the first position shown. In order to achieve that to move the impeller 18 in the in Fig. 2 shown second position, a hydraulic force F ₃ can be constructed, which acts on the second, the impeller side facing the control disk 38, 46 is disposed in the connecting channel 46, a control element 48 for controlling the flow through the connecting channel 46, which as a simple throttle or can be designed as a switchable valve.

The connecting channel 46 is particularly advantageous when the hydraulic resistance in the heating part before the consumer, ie in particular in the primary heat exchanger 12, is very large. In this embodiment, the consumers form the space heating circuit 6 and the secondary heat exchanger 8. If the hydraulic resistance in this heating part is very large, the pressure p ₂ at the branch point 10 becomes too low to exert a suitable hydraulic force F ₁ on the impeller.

If the control element 48 is designed as a switchable valve, then the connecting channel 46 can be closed, so that no hydraulic pressure F _{1 can} build up in the receiving space 43 and initially a hydraulic force F ₃ builds up over the first inlet channel 34 second side 42 of the control disk 38 acts. This hydraulic force F ₃ then leads to the axial displacement of the impeller 18 from the in Fig. 1 shown position in the Fig. 2 shown position, in which case additionally the control disk 38 with its peripheral wall 37 closes the connecting channel 36. If the control 48 is designed as a throttle, it can be ensured by a suitable design of the throttle, that at a fast start of the drive motor from the in Fig. 1 shown first position over the space heating circuit 6 in the first inlet channel 34 faster pressure p ₃ builds up than via the connecting channel 46, a pressure p ₂ in the receiving space 43. Thus, the hydraulic force F ₃ , which acts on the second side of the control disk 38 , rise faster and lead to the desired axial displacement of the control disk 38 together with the shaft 16 and the impeller 18. Instead of providing a separate control in the form of a throttle, the cross-section of the connecting channel 46 can be dimensioned so that an identical effect is achieved.

When axial displacement of the control disk 38 of the in Fig. 1 shown first position in the in Fig. 2 shown second position in which the control disk 38 enters the receiving space 43 causes the gap 45 on the outer circumference of the control disk 38 while a damping, since the fluid contained in the receiving space 43 must exit through this gap from the receiving space.

Instead of switching by different accelerations of the drive motor, such switching could also take place with the appropriate structural design solely by the speed change of the drive motor 14. If the impeller 18, for example, would be arranged so that the pressure-side cover plate 44 abut a seal and the pressure-side cover plate 44 could be deliberately pressurized, an axial displacement of the impeller 18 could also be achieved by this pressurization. The pressurization could, for example, take place via a valve which, at a certain pressure in the outlet channel 30, which achieves upon reaching a certain rotational speed of the drive motor 14 is, opens, then to pressurize the pressure-side cover plate 44.

In the illustrated embodiments according to FIGS. 1 to 3 the control disk 38 may be an integral part of the impeller 18. Thus, an impeller 18 is provided which has a closed suction-side axial end face. This is formed by the control disk 38. The impeller then has a circumferential suction or inlet opening, which is formed by the gap 39. The gap 39 preferably has a surface which is 50 to 150% of the cross-sectional area in the interior of the impeller 18 in the region of the gap 39. This inner cross-sectional area extends transversely to the longitudinal axis X. In this way, a sufficiently large flow cross-section is ensured in the region of the gap 39. In addition, it can be seen that such an impeller 18 in the region of the gap 39 has a cylindrical extension of constant cross section, which allows the axial displacement of the gap 39 between the inlet channels 34 and 36. The control disk 38 may be connected to the remaining parts of the impeller 18 via suitable webs or connecting elements in the interior or else, as shown here, by the shaft 16.

For holding the impeller in the described positions, in particular in the FIGS. 1 and 3 In addition, a corresponding speed control of the drive motor 14 can take place, by which it is ensured that a certain flow or a certain flow rate is not exceeded, at which the hydraulic force F ₂ would rise so far that it leads to an axial displacement the impeller 18 comes, which is undesirable in this situation.

The described magnetic restoring force M could also be assisted or replaced by a spring force. So could For example, in the receiving space 43, a compression spring are arranged which exerts a compressive force generated in the axial direction X on the axial end face of the shaft 16, which the shaft 16 with the rotor 24 and the impeller 18 in the in FIGS. 1 and 3 shown first position presses.

Finally, the control disk 38 could be designed as a fixed, ie not together with the shaft 16 rotating component and the shaft could only come with its front side on the control disk 38 slidably to the plant. Thus, the control disk 38 could still exert a directed in the direction of the hydraulic force F ₁ axial force on the shaft. By appropriate positive engagement, the control disk 38 could also transmit a hydraulic force F ₃ in the axial direction of the shaft 16, without having to rotate together with this.

Furthermore, it is to be understood that more than the two possible operating positions of the impeller 18 shown could also be realized. In particular, the impeller 18 could possibly take intermediate positions, whereby a mixing function could be realized. So could such a pump unit, for example, as a mixer, for. B. for a floor heating circuit, act. Then, for example, the first inlet channel 34 would be connected to the heating water inlet, while the second inlet channel 36 would be connected to the return from the underfloor heating circuit and the outlet channel 30 would be connected to the inlet side of the underfloor heating circuit. By axial displacement of the impeller 18 then a mixing function could be achieved because depending on the position more or less fluid is conveyed from the Heizwasserzulauf and a correspondingly smaller or higher proportion of fluid is conveyed from the return of the Fußbodenheizkreises. Such a defined displacement of the impeller 18 also in intermediate positions can by speed change of the drive motor with concomitant pressure change or caused by additional control elements. For example, the stator 22 could be displaced in the axial direction X to move the axial center S of the stator and thereby at the same time to displace the rotor 24, which, as described above, endeavors to center in the stator 22 in the axial direction ,

In addition, such a pump unit, as described above, instead of optionally two different heating circuits to operate as parts of a heating system, could also be used so that it optionally fluid from two different heat sources or heat generators, such as a fossil-fired boiler and a solar thermal Facility promotes. In such a case, instead of the space heating circuit 6 and the secondary heat exchanger 8, for example, two different heat sources could be connected to the pump unit 2.

LIST OF REFERENCE NUMBERS

2

- Pump unit

4

- Heating system

6

- Heat exchanger or secondary heat exchanger

8th

- Space heating circuit

10

- branch point

12

- primary heat exchanger

14

- Drive motor

16

- Wave

18

- Wheel

20

- Canned tube

22

- stator

24

- Rotor

26

- Camp

28

- Outlet openings

30

- outlet channel

32

- Suction mouth

34

- first inlet channel

36

- second inlet channel

37

- peripheral wall

38

- Control disc

39

- split

40

- first side of the control disc

42

- second side of the control disc

43

- Recording room

44

- pressure-side cover plate

45

- split

46

- Connection channel

48

- Control

50

- wall

52

- Poetry

54

- breakthrough

p ₁

- Pressure in the outlet channel

p ₂

- Pressure at the branch point

p ₃

- Pressure in the inlet channel

a

- axial displacement

X

- longitudinal axis

M

- magnetic restoring force

F ₁

- hydraulic axial force

F ₂

- hydraulic power

Claims (25)

Pump unit (2) with an electric drive motor (14) and at least one driven by this impeller (18), wherein the impeller (18) in the axial direction (X) between at least a first and a second position is movable, wherein the impeller (18 ) is located in its first axial position in a first flow path through the pump unit (2) and promotes a fluid through this first flow path, and
the impeller (18) is located in its second position in a second flow path through the pump unit (2) and promotes fluid through this second flow path, characterized in that
the pump unit (2) is designed such that a movement of the impeller (18) takes place between the first and the second position at least in one direction by a hydraulic force acting on the impeller (18) and produced by the conveyed fluid. Pump unit according to claim 1, characterized in that the pump unit (2) is equipped so that the impeller (18) is held in operation by at least one hydraulic force generated by the conveyed fluid in at least one of the positions. Pump unit according to claim 1 or 2, characterized in that the pump unit (2) is designed so that the impeller (18) in operation by an interaction of at least one hydraulic force generated by the pumped fluid, a spring force and / or an axially acting magnetic Force is held in at least one of the positions, wherein the magnetic Force preferably on a rotor (24) connected to the rotor (24) of the drive motor (14) acts. Pump unit according to one of the preceding claims, characterized in that the impeller (18) with a rotor (24) of the electric drive motor (14) is connected and at least one magnetic force acting in the axial direction (X) on the impeller (18) , resulting from a magnetic interaction between the rotor (24) and a surrounding stator (22), in particular from an axial offset (a) between the rotor (24) and stator (22). Pump unit according to one of the preceding claims, characterized in that the impeller (18) is arranged in its first position such that it conveys into a first outlet channel, and the impeller (18) is arranged in its second position such that it is in a second outlet channel promotes. Pump unit according to one of the preceding claims, characterized in that the impeller (18) is arranged in its first position such that it is connected at its suction side (32) with a first inlet channel (34), and the impeller (18) in its Second position is arranged such that it is connected at its suction side (32) with a second inlet channel (36). Pump unit according to one of the preceding claims, characterized in that the pump unit (2) is designed such that the hydraulic force by a certain operating mode of the drive motor (14), in particular by a speed change, can be generated. A pump unit according to claim 7, characterized in that the pump unit (2) is designed such that the hydraulic force can be generated by differently strong accelerations of the drive motor (14). Pump unit according to one of the preceding claims, characterized in that it is designed as a bistable system in which the impeller (18) is kept stable in operation in its first or second position by the operative hydraulic and / or magnetic forces. Pump unit according to one of the preceding claims, characterized in that the impeller (18) is located in its first position axially closer to the stator (22) of the drive motor (14) than in its second position. Pump unit according to one of the preceding claims, characterized in that the pump unit (2) is designed such that in the first position of the impeller (18) acting in the direction of the first position hydraulic force on a suction side axial end face of the impeller (18) or a pressure element (38), which is coupled to transmit force to the impeller (18) acts. Pump unit according to one of the preceding claims, characterized in that the pump unit (2) is designed such that in the first position of the impeller (18) acting in the direction of the first position magnetic force acts on the impeller. Pump unit according to one of the preceding claims, characterized in that the pump unit (2) is designed such that at least in the second position of the impeller (18) acting in the direction of the second position hydraulic force on a pressure-side axial end face (44) of the impeller (18) works. Pump unit according to claim 13, characterized in that the pump unit (2) is designed such that in the second position of the impeller (18) has a suction axial end side of the impeller or with the impeller (18) coupled pressure element (38) is depressurized. Pump unit according to one of the preceding claims, characterized in that at least one connecting channel (46) is present, which is located downstream of the impeller (18) pressure region (30) with a side facing away from the pressure region (40) of the impeller (18) or with a The pressure element (38) coupled to the impeller (18) for transmitting a hydraulic pressure, wherein in the connecting channel (46) preferably a control element (48) for controlling the flow through the connecting channel (46) is arranged. Pump unit according to one of the preceding claims, characterized in that a receiving space (43) is present, in which a closed suction-side axial end face of the impeller (18) or with the impeller (18) coupled to the pressure element (38) in at least one position of the impeller (18) occurs and which is designed such that it, preferably via a throttle point, with one of the impeller (18) generated hydraulic pressure (p ₂ ) for generating a hydraulic force can be acted upon. Heating installation with a pump unit according to one of the preceding claims, characterized in that the heating system has at least two system parts (6, 8), of which a first system part (6) with the first flow path of the pump unit (2) and a second system part (8). is connected to the second flow path of the pump unit (2). Heating installation according to claim 17, characterized in that the at least two system parts (6, 8) are at least two consumers or at least two heat sources. Heating system according to one of claims 17 or 18, characterized in that the first part of the plant is a heat exchanger (6) for domestic water heating and the second part of the plant is a space heating circuit (8). Heating installation according to one of claims 17 to 19, characterized in that the heating system is designed such that at a branch point (10) between the first and the second part of the system prevailing hydraulic pressure in at least one of the positions of the impeller (18) has a hydraulic force causes, which keeps the impeller (18) in this position. Heating boiler with a pump unit according to one of the preceding claims 1 to 16, characterized by a primary heat exchanger (12), a secondary heat exchanger (6) for domestic water heating and at least one connection for a space heating circuit (8), wherein the secondary heat exchanger (6) and the connection for the Space heating circuit (8) via a branch point (10) are connected to the primary heat exchanger and a at the branch point (10) prevailing hydraulic pressure in at least one of the positions of the impeller (18) a hydraulic force causes, which keeps the impeller (18) in this position. Impeller for a centrifugal pump assembly, in particular according to one of the preceding claims, having at least one outlet opening (28) and at least one inlet opening (39),
characterized in that
the inlet opening (39) is located in a peripheral portion of the impeller (18). An impeller according to claim 22, characterized by a closed suction-side axial end (38) to which the peripheral portion adjacent to the inlet opening (39). Impeller according to claim 22 or 23, characterized in that the inlet opening (39) is formed as an over the entire circumference of the impeller (18) extending annular opening. Impeller according to one of claims 22 to 24, characterized in that the impeller (18) has on its suction side an elongated cylindrical portion, which preferably has an outer surface which is 50 to 150% of an internal cross-section inside this portion.

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