Patent Description:
In particular in smaller buildings compact heating systems are used for heating the building and providing domestic hot water. Those systems commonly comprise a hydraulic valve device for switching the flow of heating medium between a heating circuit in the building and a heat exchanger for heating the domestic water.

From <CIT> it is known to integrate such a valve device into the circulator pump device such that the valve element of the valve device is shifted between two possible valve or switching positions by use of the water flow produced by the pump. <CIT> discloses a centrifugal pump assembly having a rotational valve element which is moved by a fluid flow through the valve element. To reduce a torque rotating the valve element guide vanes are arranged in the interior of the valve element inside a flow path of the valve element. <CIT> discloses a pump device for a dishwasher having a rotational valve element arranged in a flow path at the outlet side of a pump. <CIT> discloses a pump device having a valve element inside the pump housing.

It is the object of the invention to further improve such a centrifugal pump assembly comprising a valve element driven by the fluid flow such that a more reliable switching of the valve between the two possible switching or valve positions can be achieved.

This object is achieved by a centrifugal pump assembly comprising the features defined in claim <NUM>. Preferred embodiments are disclosed in the dependent subclaims, the following description as well as the accompanying drawings.

The centrifugal pump assembly according to the invention comprises an electric drive motor and at least on impeller driven by said electric drive motor. The electric drive motor may have a rotor, preferably a permanent magnetic rotor connected to the impeller via a rotor shaft. The electric drive motor in particular may be a wet running electric drive motor with a rotor can between the rotor space and the stator space containing the stator windings of the drive motor. In this design the rotor space is filled by the liquid to be pumped, in particular water. The impeller is rotating inside a pump housing having at least one inlet and one outlet port. The centrifugal pump assembly further comprises a valve device integrated into the centrifugal pump assembly. The valve device comprises a valve element which is rotatable between two possible valve or switching positions. The valve element is moved between these valve positions by a fluid flow produced by said impeller, in particular a fluid flow flowing in circumferential direction around the impeller. The valve element may be designed to selectively open two inlet ports or to selectively open two outlet ports of the centrifugal pump assembly. Thereby, the valve element may change the fluid flow for example between a heating circuit for heating a building and a heat exchanger for heating domestic water.

The valve element comprises a cover plate extending transversely to the rotational axis of the impeller and facing the impeller. Preferably, this cover plate extends parallel to the face side of the impeller, in particular a face side of the impeller comprising a suction port in its center. The cover plate of the valve element preferably forms one of the walls delimiting a pump space inside which the impeller is arranged. The cover plate preferably is in contact with the fluid flow on the outside of the impeller, in particular of a fluid flow in rotational direction inside the pump space.

According to the invention the valve element comprises protrusions arranged on an outer surface side facing away from the impeller such that a flow can act on them for driving the valve element. The fluid flow produced by the impeller may act on these protrusions so that the protrusions constitute force application surfaces onto which a force provided by the flow or fluid is applied such that it produces a torque acting on the valve element and rotating the valve element around its rotational axis. Since the protrusions are arranged on a surface of the valve element facing away from the impeller, a disturbance of the fluid flow in the direct surrounding area of the impeller is reduced. Thereby a high efficiency of the centrifugal pump can be maintained. The hydraulic resistance produced by the valve element is minimized.

The protrusions are provided on the outer circumference of the valve element, i. on an outer surface side of the valve element forming the outer circumference of the valve element. Thus, the protrusions are not arranged on a surface facing towards the impeller such that they are not arranged inside the fluid flow in the direct surroundings of the impeller. Thereby, the hydraulic resistance is minimized.

According to invention the protrusions are extending in radial direction related to the rotational axis of the valve element. For example, the protrusions extend in radial direction from an outer circumferential surface of the valve element. Thus, the protrusions may form a tooth-like structure on the outer circumference of the valve element substantially like a toothed wheel. The gap between the outer circumference of the valve element and a surrounding wall of the housing may be open towards the space containing the impeller such that a fluid flow produced by the impeller may directly impinge on the protrusions arranged on the outer circumference of the valve element. According to a further possible design the protrusion may be inclined in the circumferential direction. The protrusions may form inclined vanes so that a fluid flow flowing in parallel to the rotational axis of the valve element impinges on the inclined surface of the protrusion such that a force in circumferential direction, i.e. a torque acting on the valve element is produced. The protrusions inclined in circumferential direction are inclined with respect to the rotational axis, i.e. an angle between an axis parallel to the rotational axis of the valve element and the surface of the protrusion is between <NUM>° and <NUM>°, preferably between <NUM>° and <NUM>°. The protrusions may extend straight or curved to optimize the fluid flow and the torque acting on the valve element.

Further preferably, in the radial direction the cover plate extends beyond the protrusions, i.e. the cover plate preferably has a diameter greater than the diameter of a circle along the radial outer ends of the protrusions. This means the cover plate covers the protrusions on a side facing towards the impeller. The cover plate, therefore, extends between the impeller and the protrusions. Thus, the fluid flow acting onto the protrusions has to flow around the cover plate or through a gap surrounding the cover plate. Such a flow in particular may be a side flow produced by the impeller, not the main flow leaving the impeller towards an exit port of the pump assembly. In particular the side flow may be a side flow appearing only during an operational condition for movement of the valve element and not during the normal operation of the centrifugal pump. By this, the flow resistance during normal operation can be further reduced.

According to a further possible embodiment of the invention the rotational axis of the valve element extends parallel to the rotational axis of the impeller and further preferably along the rotational axis of the impeller. This allows a compact arrangement of the impeller and the valve element in one housing. Furthermore, the flow, in circumferential direction, produced by the impeller also flows circularly around the rotational axis of the valve element, thus allowing an optimized hydraulic force or torque transfer between the impeller and the valve element by this fluid flow produced by the impeller.

According to a further embodiment the valve element is arranged inside a housing having a circular inner wall surrounding the outer circumference of the valve element with a ring-shaped gap between the outer circumference of its cover plate and this inner wall. A fluid flow produced by the impeller may enter this gap such that it can act on the protrusions of the valve element, which are arranged on the outlet side of this gap, i. on a side of the cover plate facing away from said impeller. According to a further preferred embodiment the cover plate, the valve element and the surrounding wall may be designed such that the gap is substantially closed during normal operation or such that a fluid flow through this gap in another way is inhibited during this normal operation to reduce the hydraulic resistance during normal operation. This may be achieved for example by a linear movement of the valve element closing the gap and/or interrupting the flow path for fluid side flow through the gap into the region in which the protrusions are arranged.

Preferably said protrusions are evenly distributed over the outer circumference of the valve element. By this design an even force or torque transfer onto the valve element can be achieved.

According to a preferred embodiment the protrusions are of tooth-like shape and preferably are extending normally to a cylindrical outer circumferential wall of the valve element, i.e. substantially radially to the centre of the valve element. The valve element, thus, at least partly has the shape of a toothed wheel. The protrusions provide force application surfaces extending in radial direction so that a fluid flow in circumferential direction impinges on these surfaces to create a torque acting on the valve element for rotation of the valve element between the possible valve positions.

According to a further preferred embodiment the protrusions are integrally formed with an outer circumferential wall and/or the cover plate of the valve element. For example the valve element may at least partly be made from plastic material, for example by injection molding. The protrusions are preferably formed in such a part of the valve element formed from a plastic material. This allows an economic production of the valve element comprising the protrusions.

The cover plate of the valve element preferably comprises a central outlet opening being in engagement with a suction mouth of the impeller. The valve element in particular may be a valve element switching the flow on the suction side of the impeller between two possible flow paths, i. between two different suction ports. For example one suction port may be connected to a heating circuit of a building and the other suction port may be in connection with a heat exchanger for heating domestic hot water. By changing the valve or switching position one of the flow paths may be closed and the other flow path opened. Preferably the flow paths are both ending in the central outlet opening forming a connection to the suction mouth of the impeller so that a fluid flow between a suction port of the centrifugal pump assembly and the suction mouth of the impeller can be established through the valve element.

According to a further preferred embodiment of the invention said valve element is supported on a central bearing post or pivot and fixed in axial direction on this bearing post by an O-ring, wherein the O-ring preferably engages into a notch on the outer circumference of the bearing post. The O-ring has the function of a retaining ring or spring lock washer, respectively. However, the arrangement of the O-ring has at least two advantages. The O-ring has a damping function in axial direction if the valve element abuts against this O-ring. Furthermore, the O-ring can easily be mounted without special tools which allows an easy service in the field. The O-ring forms an axial stop or abutment for the valve element, in particular if the valve element is movable in axial direction as discussed below. The bearing post for example is provided with a circumferential notch or groove on the outer circumference close to its free end. Into this notch the O-ring is inserted such that it protrudes in radial direction. The protruding part of the O-ring, then, forms the abutment.

The bearing post, preferably is attached to an internal surface of a pump housing and preferably integrally formed with at least this internal surface of the pump housing. The pump housing for example may be made from plastic material or metal. This allows to integrally form the bearing post together with the pump housing. In an alternative embodiment the bearing post may be inserted into a receptacle formed in the inner surface of the pump housing, for example in form of a hole or threaded hole. In such an embodiment the bearing post may be pressed or screwed into the hole in the bottom surface of the pump housing. The valve element, preferably is mounted slidable on the bearing post such that a plane bearing is formed between the outer circumference of the bearing post and an inner circumference of a bearing hole inside the valve element.

According to a further special embodiment of the invention the valve element comprises at least one sealing portion for selectively closing a first and a second inlet port such that in a first valve position the first inlet port is closed and in a second valve position the second inlet port is closed. In a special embodiment it may be possible that there are provided two sealing portions, one for the first inlet port and one for the second inlet port, so that in a first valve position the first sealing portion closes the first inlet port and in a second valve position a second sealing portion closes the second inlet port, whereas the other inlet port is opened. Preferably, the valve element allows to change the flow path between the two inlet ports to selectively open one of the flow paths towards the entrance side of the impeller. For example the valve element may be used to switch between a heating circuit and a heat exchanger for heating domestic water in a heating system.

According to a further preferred embodiment the valve element additionally is movable in linear direction along its rotational axis. This allows the valve element to carry out a further switching movement or action, respectively. In particular by this linear movement a switchable coupling or clutch can be realized. For example in a first axial position the clutch can be engaged such that the valve element is fixed in its rotational direction. In a second axial position the valve element may be released such that it is movable in rotational direction to be moved between the two possible valve positions. Preferably, the valve element is movable in linear direction such that in the first axial position the at least one sealing portion is in sealing contact with an opposed valve seat and in the second axial position the sealing portion is distanced from the opposed valve seat. Thus, in the first axial position by the engagement with the sealing and possibly with a further engagement surface the valve element is fixed in its rotational direction so that it cannot be moved in rotational direction between the valve positions. Furthermore, a secure sealing is ensured. In the second axial position the valve element is released from the valve seat such that an engagement with the valve seat and possibly a further engagement surface is released and, preferably, the valve element is freely rotatable about its rotational axis to be moved between the valve positions by the flow produced by the impeller. By this axial movement independent from the rotational movement between the valve positions the sealing engagement and the change of the valve positions are decoupled having the advantage that for movement between the valve positions no friction forces occurring from the sealing engagement of the sealing portions have to be overcome. By this the necessary torque or forces for movement of the valve element between the valve positions are reduced.

According to a further embodiment the valve element comprises at least one inlet opening being in flow connection with an outlet opening of the valve element and arranged such that in the first valve position the inlet opening is facing a second inlet port and in the second valve position is facing a first inlet port. This means in a first valve position the inlet opening is opened towards the second inlet port and in a second valve position is opened to the first inlet port so that in the first valve position a fluid flow from the second inlet port through the valve element towards the impeller is established. In the second valve position a respective flow from the first inlet port towards the inlet side of the impeller is established. This by rotational movement of the valve element allows to change the flow path between the two inlet ports to selectively suck liquid or water out of one of the two inlet ports.

In a further embodiment the valve element may comprise a sealing member surrounding the inlet opening and arranged such that in a first axial position of the valve element the sealing member is in contact with an opposing sealing surface or valve seat and in a second axial position of the valve element the sealing member is distanced from this sealing surface or valve seat respectively. Furthermore, preferably said sealing member surrounding the inlet opening of the valve element is arranged on the outer circumference of the valve element. The sealing member provides a closed flow path from one of the inlet ports through the inlet opening and the valve element towards the impeller. Furthermore, preferably the sealing element closes a flow path around the valve element during normal operation of the pump. This may be a flow path for a side flow through the gap between the outer circumference of the valve element, in particular its cover plate, and a surrounding wall of the pump housing. If the valve element is in its axial position distanced from the sealing surface there may occur a side flow from the impeller through the gap surrounding the valve element towards the inlet opening of the valve element. Due to the rotational movement of the impeller this side flow has a spin around the rotational axis of the valve element acting on the protrusions to produce a torque acting on the valve element for its rotational movement. By changing the rotational direction of the impeller, for example by a respective motor control of the drive motor, the direction of the spin can be changed and thus the valve element can be moved into opposite rotational directions to move the valve element between two possible valve positions. In particular by pressure increase produced by the impeller the valve element can be moved in axial direction along the rotational axis such that the sealing members come into contact with an opposing sealing surface and interrupting the side flow acting on the protrusions so that the torque acting on the valve element is reduced. Furthermore, by contact between the sealing member and the sealing surfaces a frictional engagement can be achieved holding the valve element in the respective valve position, preferably even if the rotational direction of the impeller is changed again. If the sealing member surrounding the inlet opening is arranged on the outer circumference of the valve element a great radial distance between the region of frictional engagement and the rotational axis of the valve element can be achieved resulting in a greater holding torque for fixing the valve element in its valve position.

Further preferably, the sealing member surrounding the inlet opening may be arranged on an axial end of the valve element opposite to the axial end formed by the cover plate. Thus, a pressure acting on the cover plate may move the valve element in its axial direction such that the sealing member is pressed again a sealing surface, preferably a sealing surface provided on the bottom side of the pump housing. By this, a frictional engagement can be achieved to hold the valve element in its respective valve position described before.

In the following the invention is described by example with reference to the accompanying figures.

The centrifugal pump described as an example is a centrifugal pump provided for a heating system. This centrifugal pump device includes a hydraulic valve device which can be used in the heating system to change the fluid flow between a heating circuit through a building and a heat exchanger for heating domestic water.

The centrifugal pump device has an electric drive motor <NUM> comprising a motor housing <NUM> inside which the stator and the rotor are arranged. On one axial end of the motor housing, in direction of the longitudinal axis X, there is arranged an electronics housing <NUM> comprising the control electronics <NUM> for the electric drive motor. On the opposite axial end the motor housing <NUM> is connected to a pump housing <NUM> comprising an outlet connection <NUM> connected to an outlet port <NUM> in the inside of the pump housing <NUM>. The outlet port <NUM> is arranged on the outer circumference of a pump space inside which the impeller <NUM> is arranged. The pump housing <NUM>, further, comprises two inlet connections <NUM> and <NUM>. The first inlet connection is provided for a connection to a heating circuit in a building, whereas the second inlet connection <NUM> is provided for connection to a heat exchanger for warming domestic hot water. The first inlet connection <NUM> is in fluid connection with the first inlet port <NUM> inside the pump housing <NUM>. The second inlet connection <NUM> is in connection with a second inlet port <NUM> inside the pump housing <NUM>. The inlet ports <NUM> and <NUM> are arranged in one flat plane perpendicular to the longitudinal or rotational axis X. The rotational axis X is the rotational axis of the impeller <NUM> and the valve element <NUM> described in more detail later. The first and the second inlet ports are arranged in the bottom of the pump housing <NUM> seen in the longitudinal direction X.

The valve element <NUM> is arranged to switch over the flow path towards the impeller <NUM> between the two inlet connections <NUM> and <NUM>. Basically, the function of this hydraulic valve device is similar as disclosed in <CIT>. The valve element <NUM> has a central outlet opening <NUM> facing the suction mouth <NUM> of the impeller <NUM> or being in engagement with the suction mouth <NUM> such that fluid flows from the outlet opening <NUM> into the suction mouth <NUM>.

The valve element <NUM> is rotatable about the rotational axis X which corresponds to the rotational axis X of the impeller <NUM>. The valve element <NUM> is arranged on a pivot or bearing post <NUM> fixed in the bottom of the pump housing <NUM>. In this embodiment the pivot is molded into the material of the pump housing <NUM>, for example in an injection molding process. However, the bearing post may be fixed in the bottom of the pump housing <NUM> in different manner, for example being screwed into a threaded hole or being formed integrally with the pump housing <NUM>. The bearing post <NUM> extends from the bottom of the pump housing <NUM> in the longitudinal direction X into the interior of the pump housing <NUM>. The valve element <NUM> is rotatable about the longitudinal axis X and movable in a linear direction on the bearing post <NUM> along the longitudinal axis X in a certain distance. This certain distance is limited by an O-ring <NUM> forming an axial stop or abutment for the valve element <NUM>. The O-ring <NUM> engages into a circumferential groove or notch <NUM> arranged close to the free distal end of the bearing post <NUM>. The O-ring <NUM> forms an elastic axial stop and allows an easy assembling without special tools.

In this embodiment the valve element <NUM> is composed of two parts, a support member <NUM> and a cover member <NUM> which are connected by a snap fit. On the inner surface of the cover member <NUM> there are arranged engagement hooks <NUM> which embrace or engage with engagement shoulders or projections <NUM> in the interior of the support member <NUM>. The cover member <NUM> has a cover plate <NUM>, i.e. a cover of plate like shape, and is completely closed except the central outlet opening <NUM>. When arranged inside the pump housing <NUM> the cover plate <NUM> of the cover member <NUM> forms one axial wall of the pump space <NUM> inside which the impeller <NUM> is rotating. The opposite axial wall of the pump space <NUM> is formed by a bearing plate <NUM> holding one bearing for the rotor shaft <NUM>. Opposite to the cover member <NUM> there is connected a spring support <NUM> to the support member <NUM>. Between the spring support <NUM> and the support member <NUM> there is arranged a helical compression spring <NUM>. The spring <NUM> with one axial end abuts against an interior bottom surface of the spring support <NUM> and with the opposite axial end abuts against apportion of the support member <NUM>. The spring support <NUM> overlaps with elastic engagement hooks <NUM> such that the engagement hooks <NUM> engage with openings or cut-outs <NUM> in the outer circumference of the spring support <NUM> from the inside of the spring support <NUM>. Thereby the spring support <NUM> is guided on the outside of the legs of the engagement hooks <NUM> in axial direction X such that the spring support <NUM> is movable in this axial direction on the outside of the legs of the engagement hooks <NUM>. Furthermore, on the support member <NUM> there is provided a rib <NUM> in the spring support <NUM>. Rib <NUM> and slot <NUM> allow a relative movement in axial direction, but ensure a torque transfer so that the spring support <NUM> is connected to the support member <NUM> substantially torque proof except a limited play in circumferential direction between the rib <NUM> and the slot <NUM>. This play ensures a damping effect provided by torsion of the compression spring <NUM> since the spring <NUM> is in the flux in rotational direction until the rib <NUM> abuts on one of the edges of the slot <NUM>.

On the axial end opposite to the support member <NUM> the spring support <NUM> comprises a bearing portion <NUM> movably supported on the bearing post <NUM>, i.e. sliding on the outer circumference of the bearing post <NUM>. A further bearing portion <NUM> in bearing contact with the bearing post <NUM> is formed in the support member <NUM>. The bearing portion <NUM> comprises a shoulder protruding in radial direction. Against this shoulder the axial end of the compression spring <NUM> abuts.

The compression spring <NUM> forces the bearing portions <NUM> and <NUM> away from each other and forces the valve element <NUM> in an axial direction towards the motor housing <NUM>. Under compression of the spring <NUM> the valve element <NUM> may be moved towards the bottom side of the pump housing <NUM>, i.e. away from the impeller <NUM> and the motor housing <NUM>. These two possible axial positions of the valve element <NUM> are shown in <FIG> and <FIG>. In <FIG> the valve element <NUM> is in its first axial position in which the valve element <NUM> abuts against a circular shoulder <NUM> in the interior of the pump housing <NUM>. The shoulder <NUM> extends in radial direction from the inner circumference of the pump housing <NUM> providing a circular sealing surface extending substantially perpendicular to the longitudinal axis X. The valve element <NUM> is in sealing contact with this shoulder <NUM> via an elastic sealing <NUM> on the outer circumference of the support member <NUM>. This sealing <NUM> ensures a sealing of the pump space <NUM> towards the suction side of the pump device. <FIG> shows a second axial position of the valve element <NUM> in which the valve element <NUM> is moved towards the impeller <NUM> such that the sealing <NUM> is not in contact with the shoulder <NUM> anymore, but distanced from the shoulder <NUM>. In this position the valve element <NUM> is freely rotatable about the longitudinal axis X. If the sealing <NUM>, however, is in contact with the shoulder <NUM> a rotation of the valve element <NUM> is prohibited due to the frictional forces between the sealing <NUM> and the shoulder <NUM>. Thus, the shoulder <NUM> and the sealing <NUM> act as a detachable coupling or clutch. The valve element <NUM> is moved into the released position shown in <FIG> by the spring forces of the compression spring <NUM>. Into the fixed position as shown in <FIG>, in which the sealing <NUM> is in contact with the shoulder <NUM>, the valve element <NUM> is moved by the pressure produced by the impeller <NUM> and acting on the cover member <NUM> surrounding the outlet opening <NUM>. Thus, the valve element <NUM> can selectively be moved in axial direction depending on the pressure produced by the pump on the outlet side of the impeller <NUM>. This can be controlled by speed control and regulation carried out by the control electronics <NUM> arranged in the electronics housing <NUM>.

The valve element <NUM> comprises two sealing portions <NUM> and <NUM>, i.e. a first sealing portion <NUM> and a second sealing portion <NUM>. The two sealing portions <NUM> and <NUM> are arranged on the outer axial surface of the support member <NUM>, i.e. on the axial face side of the valve element <NUM> facing away from the impeller and being opposed to the first and second inlet ports <NUM> and <NUM>. The two sealing portions <NUM> and <NUM> are arranged in a common plane extending perpendicular to the rotational axis X. The two sealing portions <NUM> and <NUM> are positioned diametral in relation to the axis X, i.e. in positions offset by <NUM>° about the rotational axis X. The two sealing portions <NUM> and <NUM> each comprises an elastic sealing member <NUM>, <NUM>, which in this embodiment are formed integral with the sealing <NUM> on the outer circumference of the support member. The sealing <NUM> and the sealing members <NUM> and <NUM> may be formed as a separate part or sealing arrangement connected to the support member <NUM> or connected to the support member <NUM> by an injection molding process.

The first sealing portion <NUM> is provided to selectively close the first inlet port <NUM> and the second sealing portion <NUM> is provided to selectively close the second inlet port <NUM>. Between the two sealing portions <NUM> and <NUM> there is provided an opening <NUM> in the support member <NUM> being in fluid connection with the outlet opening <NUM> and forming an entrance opening of the valve element <NUM>.

The valve element <NUM> can take two different valve positions in rotational direction about the longitudinal axis X. <FIG> shows the first valve position in which the first sealing portion <NUM> closes the first inlet port <NUM>. In this first valve position the second inlet port <NUM> is open towards the opening <NUM> in the valve element <NUM> such that a fluid flow from the inlet port <NUM> towards the outlet opening <NUM> and into the suction mouth <NUM> of the impeller24 is enabled. In this first valve position, therefore, the impeller <NUM> and thus the entire pump sucks fluid through the first inlet connection <NUM> which is connected to the fist inlet port <NUM>. In this first valve position when the valve element <NUM> is in its engaged or sealing position as shown in <FIG> the first sealing portion <NUM> with its sealing member <NUM> is pressed against a valve seat <NUM> formed by the surrounding circumference or edge of the inlet port <NUM>. By this the first inlet port <NUM> is completely closed.

In the second valve position as shown in <FIG> the first sealing portion <NUM> is rotated aside from the first inlet port <NUM> such that the first inlet port <NUM> is opened towards the opening <NUM> providing a flow path from the first inlet port <NUM> towards the outlet opening <NUM> and the suction mouth <NUM> of the impeller <NUM>. In this second valve position the second sealing portion <NUM> is moved into a position in which it covers the second inlet port <NUM> so that the second inlet port <NUM> is closed. In the engaged or sealed position of the valve element <NUM> the sealing member <NUM> of the second sealing portion <NUM> is pressed against a valve seat <NUM> formed on the outer circumference or edge of the second inlet opening <NUM>.

Deferring from the first sealing portion <NUM> the second sealing portion <NUM> is not completely closed but contains a further valve in form of a check valve forming a bypass valve <NUM> as best shown in <FIG>. The bypass valve <NUM> has an opening <NUM> in the second sealing portion <NUM> which opening <NUM> is facing the second inlet port <NUM> in the second valve position as shown in <FIG>. The bypass valve <NUM> comprises a bypass valve element <NUM> arranged between the support member <NUM> and cover member <NUM> of the valve element <NUM>. The bypass valve element <NUM> is guided in a linear direction parallel to the rotational axis X on a guiding element <NUM> engaging into the bypass element <NUM>. The bypass valve element <NUM> in its closed position abuts against a valve seat formed by the sealing member <NUM> surrounding the opening <NUM> or defining the opening <NUM> inside the second sealing portion <NUM>. The bypass valve element <NUM> is hold in this closed or sealed position by a compression spring <NUM> forcing the bypass valve element <NUM> into the shown sealed or closed position. By a pressure acting on the bypass valve element <NUM> the bypass valve element <NUM> can be moved along the guiding element <NUM> against the force provided by the compression spring <NUM> to open the opening <NUM>. The backside of the bypass valve element <NUM> facing away from the opening <NUM> is in contact with the opening <NUM> and the outlet opening <NUM>, i.e. in contact with the suction side of the pump and with the flow path towards the suction mouth <NUM> of the impeller <NUM>. Thus, the pressure on the suction side of the pump is acting onto the backside of the bypass valve element <NUM>. If the pressure difference between both sides of the bypass valve <NUM> or bypass valve element <NUM>, respectively, exceeds a predefined threshold, which is defined by the size of the bypass valve element <NUM> and the spring <NUM>, the bypass valve <NUM> opens to allow a fluid flow from the second inlet port <NUM> towards the impeller <NUM> although the second inlet port <NUM> is closed by the second sealing portion <NUM>. This functionality may be used in a heating system when a heating circuit in a building is connected to the first inlet connection <NUM>. In case that all radiators in the heating circuit are closed there would be no fluid flow through this first inlet connection <NUM>. In this condition the pressure on the suction side of the impeller <NUM> and, therefore, on the backside of the bypass valve element <NUM> will reduce to such an extend that the pressure difference across the bypass valve <NUM> exceeds the predefined threshold and the bypass valve <NUM> opens ensuring a fluid flow through the second inlet port <NUM> to which for example a heating exchanger for heating domestic water may be connected. In a heating system, thus, a fluid flow through the boiler can be ensured avoiding an overheating of the boiler.

The threshold for opening the bypass by the bypass valve <NUM> preferably it adjusted by exchanging the bypass valve element <NUM>. There may be provided exchangeable bypass valve elements <NUM> of different size, in particular having different sized back surfaces onto which the pressure on the suction side of the pump acts. Since the opposite surface is always defined by the cross section of the opening <NUM> it is possible to adjust the forces acting in both directions onto the bypass valve element <NUM> by changing the size of the back surface. Alternatively or in addition also the size of the surface closing the opening <NUM> can be adjusted by changing the diameter of the circular protrusion <NUM> on the bypass valve element <NUM> being in contact witch the valve seat in the sealing member <NUM>.

The valve element <NUM> is moved between the two valve positions similar as known from <CIT> by the circulating flow produced by the impeller <NUM>. If the speed of the electric drive motor is reduced or the motor is switched off by the control electronics <NUM> the pressure in the pump space <NUM> is reduced such that the compression spring <NUM> moves the valve element <NUM> in its released position as shown in <FIG>. In this position the valve element <NUM> can be rotated about the rotational axis X by a circulating fluid flow inside the pump space <NUM>. The direction of the fluid flow depends on the rotational direction of the impeller <NUM>. The two valve positions are each defined by an end stop. For this there is provided a circular groove <NUM> in the bottom wall of the pump housing <NUM>. This circular groove <NUM> does not define an entire circle but has an interruption in form of a web <NUM>. The opposing surfaces of this web <NUM> define the two end stops for the rotational movement of the valve element <NUM>, i.e. the end stops defining the two possible valve positions. The spring support <NUM> of the valve element <NUM> has an axial extension forming a stop element <NUM>. The stop element <NUM> has a form of a finger offset to the rotational axis X and engaging into the groove <NUM>. The stop element <NUM> can abut against the two opposing faces of the web <NUM> to define the two rotational positions corresponding to the possible valve position as described before. In this case it is advantageous that the stop is arranged in the center allowing a damping effect due to the elasticity of the parts and particularly by torsion of the compression spring <NUM> as described above. <FIG> shows the stop element <NUM> in the second valve position corresponding to the position shown in <FIG>. <FIG> shows the stop element <NUM> in the first valve position corresponding to the valve position shown in <FIG>. It can be seen that to change the valve position the valve element <NUM> rotates by <NUM>°.

To enhance the rotation of the valve element <NUM> without increasing the flow resistance during normal operation of the pump device there are provided radial protrusions <NUM> distributed over the entire outer circumference of the valve element <NUM>. The protrusions <NUM> are arranged on the backside of the cover plate <NUM> on the cover member <NUM> so that the cover member <NUM> has a cover plate <NUM> facing towards the impeller <NUM> extending in radial direction beyond these protrusions <NUM> so that the protrusions <NUM> are completely covered by this cover plate <NUM> on the side facing the impeller <NUM>. Thus, the protrusions <NUM> are arranged on the backside of the cover plate <NUM>. The cover plate <NUM> has a diameter smaller than the inner diameter of the pump housing <NUM> such that a circular gap <NUM> surrounding the outer circumference of the cover plate <NUM> is provided. The gap <NUM> provides a flow connection between the pump space <NUM> and the region in which the protrusions <NUM> are arranged. If the valve element <NUM> is in its sealed or engaged position as shown in <FIG>, substantially no fluid flow through the gap <NUM> will occur since the flow path through the gap <NUM> is closed by the sealing <NUM> on the opposite end. However, if the valve element <NUM> is in its released position as shown in <FIG> there is a gap between the sealing <NUM> and the shoulder <NUM> opening the flow path through the gap <NUM> towards the opening <NUM> of the valve element <NUM>, i.e. on the suction side of the valve element <NUM>. Thus, if the impeller <NUM> rotates, a part of the fluid flow leaving the impeller <NUM> will enter the gap <NUM> and flow towards the opening <NUM> around the valve element <NUM> towards the outlet opening <NUM>. Due to the rotation of the impeller <NUM> this side flow through the gap <NUM> has a spin in the rotational direction of the impeller acting on the rib or tooth shaped protrusions <NUM> generating a torque on the valve element <NUM> to rotate the valve element <NUM> until the stop element <NUM> abuts against the end stop provided by the web <NUM>. If, now, the speed of the impeller is increased by the control electronics <NUM> the pressure on the outside of the impeller <NUM> increases so that the valve element <NUM> is moved into its sealed position in which the sealing <NUM> comes into contact with the shoulder <NUM> and one of the sealing portions <NUM>, <NUM> comes into contact with an opposing valve seat <NUM>, <NUM>. In this operational condition a sealed valve position is reached. After this it is possible to quickly change the rotational direction of the impeller without moving the valve element <NUM> out of its present valve position. To achieve this, due to respective control by the control electronics <NUM> the electric drive motor is accelerated thus quickly that the pressure outside the impeller <NUM> generates an axial force overcoming the spring force of the compression spring <NUM> prior to establishing a circular flow rotating the valve element <NUM> into the other valve position. This allows to selectively move the valve element <NUM> into a desired valve position and afterwards to again change the rotational direction of the impeller <NUM> so that during operation of the centrifugal pump device the impeller <NUM> can always rotate in a desired optimized rotational direction. The arrangement of the protrusions <NUM> on the backside of the cover plate <NUM> has the advantage that the protrusions have an effect only if the valve element <NUM> is in its released position. During normal operation with the valve element is in its sealed position the protrusions <NUM> have nearly no effect, in particular they do not increase the hydraulic resistance in the pump space <NUM>.

The electric motor inside the motor housing <NUM> is a wet-running electric motor having a rotor can <NUM> forming the rotor space inside which the rotor shaft <NUM> with the rotor <NUM> rotates. This rotor space is filled by the liquid to be pumped, i.e. preferably water. The stator <NUM> is arranged on the outside of the rotor can <NUM> in a dry stator space inside the motor housing <NUM>.

<FIG> shows an example for the use of the centrifugal pump device <NUM> described before. The centrifugal pump device including the features described before, i.e. the valve element <NUM> and the bypass valve <NUM> are the components surrounded by the dotted line in <FIG>. The centrifugal pump device <NUM> comprises the centrifugal pump <NUM> with the electric drive motor <NUM> and the impeller <NUM>. The valve element <NUM> forming a switch over valve is arranged on the suction side of the centrifugal pump <NUM> allowing to switch the flow path between two possible inlet connections, the first inlet connection <NUM> and the second inlet connection <NUM>. On the pressure side the centrifugal pump <NUM> is connected with the outlet connection <NUM>. In this example the outlet connection <NUM> is connected to a boiler <NUM> heating the liquid, in particular water, in the heating circuit. On the outlet side of the boiler <NUM> the heating circuit branches into a first branch forming the circuit of a central heating CH which may contain several radiators <NUM> or one or more floor heating circuits, for example, and the second branch for heating domestic hot water DHW. The second branch comprises a heat exchanger <NUM> for heating domestic hot water (DHW). As can been seen, the bypass valve is in connection with the second branch, i.e. the branch containing the heat exchanger <NUM>. In case that the valve element <NUM> is in the valve position in which a flow path through the central heating circuit CH is open, the bypass valve <NUM> can prevent an overheating of the boiler <NUM>. In this valve position, if the radiators <NUM> are closed, the fluid flow through the central heating circuit CH is interrupted. In this case the bypass valve <NUM> can open due to a pressure difference overcoming the biasing force of the compression spring <NUM> such that the flow path through the heat exchanger <NUM> opens and the water is circulated by the centrifugal pump <NUM> through the second branch of the heating system, i.e. through the heat exchanger <NUM>, thereby distributing the heat produced by the boiler <NUM> in the system to avoid an overheating of the boiler <NUM>.

Claim 1:
Centrifugal pump assembly comprising an electric drive motor (<NUM>), at least one impeller (<NUM>) driven by said electric drive motor (<NUM>) and a valve element (<NUM>; <NUM>') rotatable between two valve positions driven by a fluid flow produced by said impeller (<NUM>), wherein the valve element (<NUM>; <NUM>') comprises a cover plate (<NUM>; <NUM>') extending transverse to the rotational axis (X) of the impeller (<NUM>) and facing the impeller (<NUM>),
characterized in that
the valve element (<NUM>; <NUM>') comprises protrusions (<NUM>; <NUM>') which extend radially from an outer circumference of the valve element (<NUM>; <NUM>') and are arranged on an outer surface side facing away from the impeller (<NUM>) such that a flow can act on them for driving the valve element (<NUM>; <NUM>'), to rotate the valve element (<NUM>, <NUM>') around its rotational axis.