EP3339654B1 - Centrifugal pump - Google Patents

Description

The invention relates to a centrifugal pump with at least one pump stage, with a rotatable impeller with a suction mouth, which is sealed off from a stationary pump part by means of a sealing arrangement, the sealing arrangement having a sealing ring between the impeller and the stationary pump part.

Such sealing arrangements are part of the state of the art. Out CN 2486751 Y a centrifugal pump is known in which a sealing ring is arranged on the housing side in the region of the suction mouth of the pump, which sealing ring has a sealing lip which rests on the outside of the impeller in the region of the suction mouth. The sealing lip is arranged in such a way that the contact pressure increases with increasing impeller speed, i.e. with increasing differential pressure between the pressure side and suction side of the impeller. In this way, an almost complete seal between the pressure side and suction side of the pump can be achieved, whereby overflow losses and thus efficiency losses due to overflows can be reduced, but at the same time the friction between the sealing lip and the impeller increases with increasing pressure, which leads to efficiency-reducing friction losses and wear the sealing lip leads.

In this respect, the off is cheaper DE 10 2014 116 466 B3 known sealing arrangement in which a special sliding surface is provided on the suction mouth side on the outer circumference of the impeller and a sealing ring is incorporated on the housing side, which with one edge of its free End rests against this sliding surface. With this arrangement, the friction losses and thus also the wear can be reduced, but the sealing arrangement is structurally complex and, due to the fact that a section of the sealing ring is constantly in contact with the sliding surface of the impeller, is subject to wear. The design also requires high manufacturing and assembly accuracy in order to arrange the components concentrically to one another.

The sealing of the suction mouth against the stationary pump part by means of a sealing arrangement reduces the overflow losses, but increases the friction losses within the pump, so that the requirements for a high sealing effect on the one hand and low friction losses on the other hand are contrary. In this respect, only the sealant-free reduction of the gap between the suction mouth and the stationary pump part is more favorable, but this increases the manufacturing tolerances and thus the manufacturing costs.

Out RU 2 196 254 C2 It is part of the state of the art to provide a sealing arrangement with a stationary sealing ring on its side facing the impeller with pocket-like recesses distributed evenly around the inner circumference, in these areas the sealing ring is only pressed against the pump impeller when pressure is applied, namely through the hydraulic forces on the pressure side of the impeller.

Based on this prior art, the invention according to the application is based on the object of designing a generic centrifugal pump in such a way that, on the one hand, the best possible seal between the suction mouth and the stationary pump part during operation of the pump and, on the other hand, the lowest possible friction losses.

According to the invention, this object is achieved by a centrifugal pump having the features specified in claim 1. Advantageous embodiments of the invention emerge from the subclaims, the following description and the drawing.

The basic idea of this solution according to the invention is to let the sealing ring run like a plain bearing so that at least when the pump is in delivery mode, i.e. when the impeller rotates relative to the stationary pump part, a film of liquid between the sealing ring and the surface on which it rests is built up and thus fluid friction and no solid body friction occurs between the sealing ring and the mating sealing surface. Such fluid friction minimizes the friction losses within the seal, but on the other hand allows the overflow losses within the seal arrangement to be kept extremely low. Fluid friction not only significantly reduces the friction within the seal arrangement, but also reduces wear on the seal itself to a minimum.

According to the invention, complete fluid friction does not necessarily have to be guaranteed, as is the case with a plain bearing. In the solution according to the invention, intermediate stages between fluid friction and solid-state friction can also be provided, that is to say that the spaced-apart surfaces of the sealing arrangement are intended to introduce friction-reducing fluid into the sealing gap between the sealing surface and the counter-sealing surface, but that there is not necessarily complete fluid friction, but possibly also mixed friction and, depending on the operating state, solid body friction can also occur. For example, punctiform contact can be provided in the area between the sealing surfaces that are spaced apart from one another.

The solution according to the invention can be used with single-stage as well as multi-stage centrifugal pumps, with single-stage centrifugal pumps the sealing arrangement is typically between the suction mouth of the impeller and the housing, with multi-stage arrangements between the suction mouth and a stationary pump part typically a pump stage. One or more stages can be provided with the sealing arrangement according to the invention. The centrifugal wheel is preferably a radial or semi-axial wheel, that is to say a centrifugal wheel in which the suction mouth is directed in the axial direction of the wheel and the outflow side is directed radially or axially / radially. In principle, however, the invention is not limited to this type of construction.

The basic idea of the present invention, namely to have successively abutting and non-abutting sealing sections in order to ensure the build-up of a liquid film between the seal and the mating sealing surface, can be achieved according to the invention by an embodiment according to claim 1, in which the sealing ring is at least partially elastic and the System of the sealing ring or the sealing ring sections on the mating surface is controlled by the hydraulic forces on the pressure side of the impeller.

The basic idea of this solution is to design the sealing ring with different stiffnesses over its circumference and to arrange it in such a way that when the pump is operating, i.e. when the impeller is rotating in relation to the stationary pump part, the hydraulic forces affect the sealing ring through the pressure difference between the pressure side and suction side Press the circumference to different degrees on the counter-sealing surface. It is preferably provided according to the invention that the sealing ring is designed and arranged so that it is in the idle state of the pump, that is, when the impeller is at a standstill Counter sealing surface, in particular is arranged spaced from the suction mouth. Such an arrangement in which the sealing ring only comes into contact with the counter-sealing surface due to the differential pressure between the suction and pressure side of the impeller and, due to its structure, is designed so that there are sections that contact the counter-sealing surface and alternately those that do not or do not contact the counter-sealing surface. are applied with a significantly reduced force, the principle according to the invention, in which the seal is lubricated during operation like a slide bearing by a liquid film, can also be implemented. The latter arrangement also has the advantage that the seal, i.e. the sealing ring sections in contact with the counter-sealing surface, only takes place during operation and there is also a clear gap between the sealing ring and the counter-sealing surface, which on the one hand results in a certain self-cleaning effect and on the other hand, for example, calcification of the sealing surfaces is counteracted, as these are in motion. In addition, there is a significant advantage that the tolerances in the area of the sealing arrangement are such that manufacture and assembly are simplified and thus the manufacturing costs are reduced.

The hydraulic control to the effect that sealing ring sections rest against the mating sealing surface and others are spaced apart, and this alternately, is achieved in that the sealing ring has a different stiffness distributed over its circumference, preferably alternately stiff and less stiff sections, so that when in contact hydraulic forces, the sealing ring is deliberately deformed to form adjacent sections and non-adjacent sections.

This principle is achieved in that the sealing ring has recesses on its outer circumference which weaken the cross section and which preferably extend parallel to one another. These recesses, in which the material thickness is reduced, can be arranged parallel to the longitudinal center axis of the sealing ring or also preferably at an angle to it, so that the alternately successive sections, on which the sealing surface abuts the counter-sealing surface and which they do not abut, are arranged overlapping viewed in the axial direction .

The targeted material weakening can not only be brought about by recesses on the outer circumference of the sealing ring, but also by recesses on the inner circumference. For the arrangement of the recesses, the arrangement of the sealing ring in relation to the suction mouth must be taken into account. Typically, the sealing ring is designed so that it rests against the outer circumference of the suction mouth, then the sealing ring can be freely designed on its outer circumference, whereas recesses on the inner circumference must be dimensioned so that no inadmissibly high overflow losses occur. In particular, the recesses on the inner circumference can be designed in such a way that they run out towards the suction side, so that a narrow circumferential ring is formed there, which prevents overflow.

It can be advantageous to also provide recesses on the inner circumference of the sealing ring, these being expediently arranged parallel to one another, for example axially parallel or at an angle thereto.

According to an advantageous development of the invention, the recesses are wedge-shaped as seen in the circumferential direction. Such a design has the advantage, in particular on the side of the sealing ring, which is intended to rest on the counter-sealing surface, that a liquid film is reliably created due to the wedge-shaped recesses in the direction of rotation that fill with conveyed liquid during operation is built up, which ensures low-friction sliding of the sealing ring on the mating sealing surface.

On the side of the sealing ring facing away from the mating sealing surface, the wedge-shaped recesses cause targeted material weakening, whereby due to the wedge shape the material weakening does not occur abruptly in both circumferential directions but only abruptly in one direction and increasing in the other direction, which ensures that the Sealing ring deformed in the desired way only in the desired places.

It has proven to be particularly advantageous in practice to provide such wedge-shaped recesses on both sides of the sealing ring. If, which is advantageous, the recesses are wedge-shaped in the circumferential direction, then it is advantageous to arrange the wedge-shaped recesses on the outer circumference in the opposite direction to the wedge-shaped recesses on the inner circumference. It is particularly preferred to then arrange them offset to one another. Due to the variance of the offset angle, depth and rise of the recesses, the sealing ring can be designed exactly as it is particularly advantageous for a specific application. It goes without saying that the sealing arrangement according to the invention is effective and effective for a wide speed range, but that the effectiveness is typically highest in a certain speed range. This range is expediently designed so that it is the speed range in which the centrifugal pump is likely to be operated most frequently. However, it can also be provided according to the invention to design the sealing arrangement in such a way that it is most effective in the maximum pressure range of the pump. This is useful insofar as the overflow losses in centrifugal pumps according to the state of the art are typically greatest in the maximum pressure range.

It is particularly advantageous if the sealing ring is attached to the stationary pump part and is provided for sealing against an outer surface of the impeller close to the suction mouth. As a result, the suction area of the pump is not affected, and at least when the sealing ring is arranged at a distance from the impeller, a kind of Venturi effect occurs when it starts up, which increases the pressure on the outside and causes the sealing ring to move in sections against the mating sealing surface on the outer circumference of the impeller, is accelerated. The arrangement is such that the outer circumference of the sealing ring is subjected to the pressure of the pressure side of the impeller during operation, which ultimately controls the application of the sealing ring to the impeller, in the same way as the deformation of the sealing ring. As shown in detail below, there is a large variance in the arrangement of the sealing ring, with all arrangements being the same that an outer surface of the sealing ring is subjected to the pressure on the pressure side of the impeller, while another side is intended to rest on a counter-sliding surface is, which is provided on the impeller side.

It should be pointed out that for the function of the sealing arrangement, as described at the beginning, it is basically irrelevant whether the sealing ring is arranged on the housing side or on the impeller side, but as a rule the housing arrangement, i.e. the arrangement on a stationary pump part the more favorable, since any imbalances in the sealing ring then play no role and the mass moment of inertia of the impeller is not increased by the sealing ring.

Thus, when the sealing ring is arranged on the impeller, it can preferably be arranged on the suction-side end of the impeller and a counter-sealing surface by an annular section of the stationary pump part that dips into the sealing ring - if the seal takes place radially In the case of radial sealing, the ring section is formed by a cylindrical surface arranged parallel to the axis of rotation.

In such an arrangement, it is advantageous if the sealing ring is arranged to continue the suction mouth of the impeller, i.e. if the sealing ring forms the suction mouth, which, however, is functionally displaced into the inside of the impeller due to the immersing fixed pump part. It is essential for the sealing ring that the pressure of the pressure side of the impeller is applied completely to the outside in particular, if possible.

The core idea of the solution according to the invention is to design the sealing ring in such a way that, during operation, a hydrodynamic or hydrostatic liquid film is formed between the surfaces of the sealing arrangement that are moved relative to one another. Hydrodynamically, this can be done by appropriate shaping of the sealing ring and / or its recesses, for example wedge-shaped, and hydrostatically, for example, through channels which are provided in the sealing ring and lead to the pressure side and open into the sealing surface. A combination of hydrodynamically and hydrostatically built up liquid film can also be provided.

Fig. 1

in stark vereinfachter und schematisierter Längsschnittdarstellung eine Kreiselpumpe mit einer Dichtungsanordnung gemäß der Erfindung,

Fig. 2

eine erste Ausführungsvariante der Dichtungsanordnung mit feststehendem Dichtring,

Fig. 3

eine Dichtungsanordnung in Schnittdarstellung bei Stillstand des Laufrades,

Fig. 4

die Dichtungsanordnung gemäß Fig. 3 im Betrieb der Pumpe,

Fig. 5

eine weitere Dichtungsanordnung in Darstellung nach Fig. 3,

Fig. 6

eine erste, aber nicht zur Erfindung gehörende Ausführung einer Dichtungsanordnung mit rotierendem Dichtring in Darstellung nach Fig. 3,

Fig. 7

eine alternative Anordnung mit rotierendem Dichtring in Darstellung nach Fig. 3,

Fig. 8

eine perspektivische Darstellung eines Dichtrings gemäß der Erfindung und

Fig. 9

eine alternative Ausführung des Dichtrings.

The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing. Show it:

Fig. 1

in a greatly simplified and schematic longitudinal sectional view of a centrifugal pump with a sealing arrangement according to the invention,

Fig. 2

a first variant of the sealing arrangement with a fixed sealing ring,

Fig. 3

a sectional view of a sealing arrangement when the impeller is at a standstill,

Fig. 4

the sealing arrangement according to Fig. 3 during operation of the pump,

Fig. 5

another sealing arrangement in the illustration according to Fig. 3 ,

Fig. 6

a first, but not part of the invention, embodiment of a sealing arrangement with a rotating sealing ring shown in FIG Fig. 3 ,

Fig. 7

an alternative arrangement with a rotating sealing ring shown in FIG Fig. 3 ,

Fig. 8

a perspective view of a sealing ring according to the invention and

Fig. 9

an alternative design of the sealing ring.

In the Fig. 1 The centrifugal pump shown in a highly simplified manner has a stationary pump housing 1, which has a suction connection 2 and a pressure connection 3, in which a shaft 4 is rotatably mounted, which drives a centrifugal wheel 5 seated on it, the axial suction mouth 6 of which is line-connected to the suction connection 2 and whose The outflow side 7 is arranged radially and line-connected to the pressure connection 3.

The pump housing 1 stands for any fixed pump component, for example in the case of a multi-stage pump for the fixed part of a pump stage, that is, that based on Fig. 1 The schematic representation shown can also be transferred to one or more impellers with the corresponding stationary pump parts.

Between the outflow side 7, ie the pressure side of the pump, and the suction port 6, ie the suction side of the pump, an overflow channel 8 is formed which can be shut off by a sealing ring 9 in the pump. Examples of the configuration of the sealing arrangement between the suction mouth 6 of the centrifugal pump, that is to say the suction side and the overflow channel 8 connected to the pressure side, are shown in detail on the basis of FIG Figures 2 to 7 which only schematically show a part of this overflow channel 8, the impeller 5, the pump housing 1 and the sealing ring 9.

The based on Fig. 2 illustrated sealing ring 9a, which is arranged in the same way as that based on Fig. 1 The sealing ring 9 shown has a narrow end face, in Fig. 2 its lower side attached to the fixed part 1 of the pump. It has a slim ring-cylindrical shape, the inside of the sealing ring 9a being intended to rest on the outer circumference, which is essentially cylindrical there, in the area of the suction mouth 6 of the impeller 5. In the unloaded state, the sealing ring 9a is arranged at a small distance from the outside of the suction mouth 6 of the impeller 5. It has recesses 10 distributed over its outer circumference, which are provided here parallel to one another and parallel to the longitudinal axis of the sealing ring 9a at a regular angular spacing on the outer circumference. The material of the sealing ring 9a is weakened by these recesses 10, which have a partially circular cross-section, so that the sealing ring 9a has the smallest material thickness at the base of a recess 10 and the greatest material thickness at the edge of the recess 10. The sealing ring 9a is made of elastic material and so material and Matched in size so that the gap formed between the inside of the sealing ring 9a and the outside of the suction mouth 6 of the impeller 5 is closed when the pump is in operation. This means that when the impeller 5 is driven by the shaft 4 and a pressure difference is generated between the suction mouth 6 and the outflow side 7, the hydraulic and flow forces that then set control the sealing ring 9a to rest against the impeller 5 in the outer area of the suction mouth 6. The swirl of the liquid emerging from the impeller 5 on the outflow side 7 in the area of the sealing ring 9a on the outside results in a Venturi effect which, in conjunction with the differential pressure that builds up between the outflow side 7 and the suction mouth 6, leads to the sealing ring 9a is pressed from the outside inwards. Due to the different material thickness, however, the sealing ring 9a does not rest on the outside of the suction mouth 6 over the entire circumference, but only in sections due to the different rigidity of the sealing ring 9a in the circumferential direction. Thus, the inside of the sealing ring 9a does not fully lie against the mating sealing surface 11, but instead a sealing ring section which is spaced therefrom follows in the circumferential direction and then another adjacent sealing ring section alternately over the entire circumference of the ring 9a. In the non-contacting sections of the sealing ring 9a, conveying liquid passes through the overflow channel 8 into the area between the sealing ring 9a and the counter-sealing surface 11, which is distributed over the sealing surface by the alternating contacting and non-contacting sections and the rotation of the impeller, so that in the area between the sealing ring 9a and counter sealing surface 11 there is always fluid friction.

Based on Fig. 3 and 4th is shown schematically how the sealing ring 9 attached to the housing can move out of its static position ( Fig. 3 ), in which the impeller 5 stands still, initially due to the Venturi effect building up on the outside when the impeller 5 rotates then applied to the counter-sealing surface 11 of the impeller 5 by the differential pressure between the pressure side and the suction side.

In order to build up a stable liquid film between the sealing surface 12 of the sealing ring 9 and the counter-sealing surface 11 on the impeller 5, the can be based on the impeller 9a in Fig. 2 The structure described with recesses 10 on the outer circumference of the sealing ring 9a can be used in order to generate alternately abutting and non-abutting sections between the sealing surface 12 and the counter-sealing surface 11. In addition or as a support, recesses can be provided in the surface in the sealing surface 12 or in the counter-sealing surface 11, which recesses support this effect. The details below and based on the Fig. 8 and 9 Sealing rings described illustrate how such a configuration can look.

The application of the sealing ring 9 to the suction mouth 6, as shown in Fig. 4 is shown, takes place exclusively by hydraulic forces, so that when the impeller 5 is at a standstill, the sealing ring 9 is in its in Fig. 3 resets the starting position shown, in which a gap is formed between the sealing surface 12 and the counter-sealing surface 11 in the overflow channel 8. This elastic movement of the sealing ring 9 when it is applied or reset cleans the sealing gap and ensures that no deposits form on the sealing surface 12 in particular.

Based on Fig. 5 a sealing ring 9b is shown, which has an L-shaped profile in cross-section, with an upright leg 13 based on the Fig. 3 and 4th Sealing ring 9 described corresponds to, whereas a lying leg 14 is provided for fastening the sealing ring 9b to the stationary part 1 of the pump, that is to say, for example, the pump housing 1. The fastening of the sealing ring 9b can take place in a cohesive and / or non-positive manner in that the ring 9b is pressed into the corresponding recess in the pump housing 1.

When using Fig. 6 The embodiment variant shown (not belonging to the invention) is provided with a sealing ring 9c which has the shape of an annular disk and which is firmly connected on its inner circumference to the outer circumference of the impeller 5 in the area of the suction mouth 6. The sealing ring 9c thus rotates with the impeller 5, its sealing surface 12 comes into contact with the counter-sealing surface 11 on the pump housing, whereby the differential pressure between the pressure side of the impeller and the suction side ensures that the sealing surface 12 contacts the counter-sealing surface 11 in sections. In this embodiment too, the sealing ring 9c has different stiffnesses over its circumference due to recesses not shown here, so that sections of the sealing surface 12 are formed that bear against the counter-sealing surface 11 and sections that are spaced therefrom. So that the above-described "sliding bearing effect" also occurs with this arrangement, that is to say a stable liquid film is formed between the sealing surface 12 and the counter-sealing surface 11.

When using Fig. 7 The embodiment variant shown, the sealing ring 9d is arranged on the suction-side end face of the impeller 5 as an extension of the suction mouth 6. On the housing side, a ring section 15 is provided, which is arranged inside the sealing ring 9d and extends into the suction mouth 6 of the impeller 5. The counter-sealing surface 11 for the sealing ring 9d is formed by the inside of this ring section 15. The sealing ring 9d can be designed in the same way as that based on FIG Fig. 2 described sealing ring 9a or like the one below with reference to the Fig. 8 and 9 described sealing rings.

In the variant according to Fig. 8 a sealing ring 9e is provided, Fig. 8 shows an example of how such a sealing ring 9 of FIG Fig. 3 and 4th , which consists of elastic material, for example rubber, silicone or the like, can be configured to the previously described To achieve effects. The sealing ring 9e has a total of ten wedge-shaped recesses 16 distributed over its outer circumference, the depth of which is shown in FIG Fig. 8 increase clockwise, i.e. penetrate deeper into the base material of the ring. These wedge-shaped recesses 16 alternate with sections 17 which form part of a cylinder surface. Also on the inside, that is to say on its inner circumference, the sealing ring 9e has wedge-shaped recesses 18 which are interrupted by cylindrical sections 19 which also lie on a common cylinder surface. The recesses 18 on the inside extend approximately only over a third of the circumference of the recesses 16 on the outside and over a smaller depth. The direction of the wedge shape of the recesses 18 is opposite to the direction of the recesses 16.

While the recesses 16 are used exclusively for the targeted weakening of the ring material, so that when a pressure builds up from the outside it is deliberately deformed in a bumpy manner on its inside, that is, forms sections that lie against the mating sealing surface 11 and those that are spaced from it, the recesses serve 18 on the inner circumference primarily the formation of a stable lubricating film between the sealing surface 12, that is to say the inside of the sealing ring 9e and the counter-sealing surface 11. However, these can also have an influence on the deformation of the sealing ring.

An alternative embodiment of such a sealing ring 9f is based on Fig. 9 shown. The construction of the sealing ring 9f made of an elastic material, in which wedge-shaped recesses 16a on the outside alternate with cylindrical sections 17a and in which wedge-shaped recesses 18a alternate with cylindrical sections 19a on the inside, differs from the one described above with reference to FIG Fig. 8 embodiment shown essentially in that the recesses 16a and 18a and the Sections 17a and 19a are not arranged parallel to the axis of the ring 9f but at an angle to it, namely on the outside and on the inside with the same incline, so that abutting and non-abutting portions of the sealing ring 9f result when pressure is applied from the outside, which are shown in Overlap viewed in the axial direction. This inclined position of the wedge-shaped recesses 18a on the inside achieves a certain pumping effect, which ensures that a stable liquid film is created in the sealing gap between sealing surface 12 and counter-sealing surface 11 even with high contact forces. Furthermore, the overflow losses are further reduced by these inclinations.

The above exemplary embodiments cannot even begin to reproduce the various possibilities of sealing ring designs which result from the present invention. In individual cases, it must be determined experimentally and / or mathematically how a stable liquid film is established between the sealing ring and the counter-sealing surface over the largest possible speed range of the pump in order to keep wear and friction losses on the seal as small as possible.

Claims (12)

1. A centrifugal pump with at least one pump stage, with a rotatable impeller (5) with a suction port (6) which is sealed with respect to a stationary pump part (1) by way of a sealing arrangement, wherein the sealing arrangement comprises a sealing ring (9) between the impeller (5) and the stationary pump part (1) and the sealing ring (9) at least in sections is designed in an elastic manner and the contact surface (12) of the sealing ring (9) or of the sealing ring sections on the counter surface (11) is controlled by the hydraulic forces at the delivery side of the impeller (5), wherein the sealing ring (9a, 9e, 9f) has sections of different stiffness which are distributed over its periphery, characterised in that the sealing ring (9a, 9e, 9f) on its outer periphery comprises recesses (10, 16, 16a) which reduce the cross section.
2. A centrifugal pump according to claim 1, characterised in that the recesses (10, 16, 16a) on the outer periphery of the sealing ring (9a, 9e, 9f) extend parallel to one another.
3. A centrifugal pump according to one of the preceding claims, characterised in that the sealing ring (9e, 9f) on its inner periphery comprises recesses (18, 18a) which reduce the cross section and which preferably extend parallel to one another.
4. A centrifugal pump according to claim 2 or 3, characterised in that the recesses (10, 16, 16a, 18, 18a) extend parallel to the axis direction of the sealing ring or obliquely thereto.
5. A centrifugal pump according to one of the preceding claims, characterised in that the recesses (10, 16, 16a, 18, 18a) are designed in a wedge-like manner in the peripheral direction.
6. A centrifugal pump according to one of the preceding claims 2 to 5, characterised in that the recesses are open towards the delivery side as well as towards the suction side.
7. A centrifugal pump according to claim 5 or 6, characterised in that the wedge-like recesses (16, 16a) on the outer periphery and the wedge-like recesses (18, 18a) on the inner periphery are directed oppositely to one another and preferably are arranged offset to one another.
8. A centrifugal pump according to one of the preceding claims, characterised in that the sealing ring (9, 9a, 9b) is arranged on the stationary pump part (1), and is arranged close to the suction port (6), for sealing with respect to the outer surface of the impeller (5).
9. A centrifugal pump according to one of the preceding claims, characterised in that the sealing ring (9d) is arranged on the impeller (5), preferably at the suction-side end of the impeller (5), and a counter sealing surface (11) is formed by a ring section (15) of the stationary pump part (1) which immerses into the sealing ring (9d).
10. A centrifugal pump according to one of the preceding claims, characterised in that the sealing ring (9c) is arranged on the impeller (5), preferably at the suction-side end of the impeller (5), and a counter sealing surface (11) is formed by an annular surface of the stationary pump part (1).
11. A centrifugal pump according to one of the preceding claims, characterised in that the sealing ring (9d) is arranged in a manner continuing the suction port (6) of the impeller (5).
12. A centrifugal pump according to one of the preceding claims, characterised in that the sealing ring (9) is designed such that on operation, a hydrodynamic or hydrostatic fluid film forms between the surfaces (11, 12) of the sealing arrangement which are moved to one another.

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