Wet rotor pump without axial bearing

Abstract

The invention relates to a wet rotor pump (1) with a permanent magnet rotor (2) and a pump chamber (4) bounded from the rotor (2) by a partition (5), in which an impeller (7) is arranged. The impeller is mounted non-rotatably on an axially displaceable shaft (3) and has a support disk (8), a cover disk (10), and blades (9) arranged between them. The cover disk (10) is radially sealed by means of a suction neck seal (11), and a first annular wall (12) projects from the support disk (8). This annular wall, together with an axial projection (6) of the partition (5), forms an axially flowable, radial throttle gap (13) of constant width. A relief bore (18) forms a fluid connection between the suction side (20) of the impeller (2) and an impeller side chamber located between the support disk (8) and the partition (5).The impeller (7) has a second annular wall (14) extending towards the partition (5), which divides the impeller side space between the first wall (12) and the shaft (3) into a radially outer annular space (16) and a radially inner annular space (17). Together with the partition (5), this annular wall forms a radially flowable axial throttling gap (15) that depends on the axial position of the impeller (7). The suction neck seal (11) is located on a diameter between the radial throttling gap (13) and the axial throttling gap (15). The relief bore (18) opens into the radially inner annular space (17). As a result of this design, the gap width of the axial throttling gap (15), and thus the axial position of the impeller, adjusts itself automatically. Therefore, a thrust bearing is not required in the wet rotor pump (1).

Description

[0001] The invention relates to a wet rotor pump with a permanent magnet rotor and a pump chamber bounded towards the rotor by a partition wall, in which an impeller is arranged which is mounted rotationally fixed on a shaft axially displaceable relative to the stator and has a support disc, a cover disc and blades arranged between them, wherein the cover disc is radially sealed by means of a suction neck seal and an annular wall projects from the support disc, which together with an axial projection of the partition wall forms an axially flowable radial throttling gap of constant gap width, and wherein a relief bore forms a fluid connection between the suction side of the impeller and a side space of the impeller located between the support disc and the partition wall.

[0002] Wet rotor pumps are centrifugal pumps in which the rotor rotates within the pumped medium. Axial forces act on the impellers of centrifugal pumps, resulting from pressure and momentum forces on the impeller surfaces. Typically, the resulting axial force opposes the inflow to the impeller and must be absorbed by a thrust bearing. In wet rotor pumps, these thrust bearings are generally designed as medium-lubricated plain bearings consisting of a stationary and a rotating component. However, a bearing system used to absorb the axial force can have disadvantages. For example, the thrust bearing requires installation space, leads to higher costs, increased system complexity, friction losses, and noise. Furthermore, it must be monitored with regard to component quality and tolerances, is subject to wear, and carries the risk of sticking. Therefore, there is a desire to eliminate the thrust bearing.

[0003] To reduce losses in the bearing system by decreasing bearing load, relief systems have been developed, which are particularly necessary in multi-stage pumps. In these systems, the axial forces can become so large that a conventional bearing can no longer accommodate them in a reasonably sized and cost-effective manner with acceptable losses. The reduced bearing load is offset by increased volumetric and / or frictional losses in the relief system. Therefore, it is essential to carefully examine in practice whether the advantages of the relief system outweigh its disadvantages. A relief system can be formed, for example, by so-called back vanes on the rear of the impeller's support disc. Furthermore, in the wet-rotor pump of this type, the projecting annular wall of the support disc and the relief bore, for example in the impeller, form a relief system to reduce the axial forces acting on the impeller.DE 27 33 631 A1 presents the prior art for the present invention and discloses a centrifugal pump with a pump rotor that compensates for axial thrusts by means of a special design. Side chambers of the impeller act as axial thrust compensation chambers, which are controlled by fluid connections.

[0004] The object of the invention is to provide a wet rotor pump with an improved relief system that eliminates the axial forces in the normal operation of the wet rotor pump, so that it can be designed without axial bearings, with the relief being housed in a space-saving manner in the wheel side space of the support disc.

[0005] This problem is solved by the subject matter of claim 1. Advantageous further developments are specified in the dependent claims and are explained below.

[0006] According to the invention, in the generic wet-rotor pump, instead of an axial bearing, the impeller has a second annular wall extending towards the partition wall. This annular wall separates the impeller side space between the first wall and the shaft into a radially outer annular space and a radially inner annular space. Together with the partition wall, it forms a radially flowable axial throttling gap, the diameter of which depends on the axial position of the impeller. The suction neck seal is located on a diameter between the radial and axial throttling gaps, and the relief bore opens into the radially inner annular space. As a result of this design, the width of the axial throttling gap, and thus the axial position of the impeller, adjusts itself automatically. Therefore, an axial bearing can be omitted in the wet-rotor pump.

[0007] According to the invention, the compensation of axial forces on the impeller is achieved by a system of interacting components, namely A radial sealing gap (radial gap) with a constant gap width on an outer diameter of the impeller. This sealing gap forms a radial pre-throttle and is traversed by axial flow. An axial sealing gap (axial gap) with a variable gap width on an inner diameter of the impeller. This sealing gap is traversed by radial inwards and forms an axial throttle, the effect of which depends on the gap width of the axial gap, which in turn depends on the axial position of the impeller or rotor. The inner diameter is understood to be a diameter that is closer to the shaft than the outer diameter. A radial sealing gap with a constant gap width, formed by the suction neck seal, on a mean diameter of the impeller, i.e., a diameter between the outer and inner diameters, in other words, between the radial gap and the axial gap.and a relief bore that opens between the inner diameter and the shaft into the wheel side chamber, thereby allowing flow through the wheel side chamber, thus enabling the radial and axial sealing gaps to become effective.

[0008] The radial choke ensures that the preferred direction of the hydraulic pressure forces acting on the impeller always points in the direction of flow at the impeller inlet. This causes the rotor to be displaced by pressure and momentum forces on the impeller in such a way that the axial sealing gap closes, i.e., its gap width decreases. This results in an increase in the pressure level in the impeller side chamber on the back side, which is dissipated via the relief bore until a force equilibrium is reached. In this equilibrium position, the rotor remains stationary with respect to its axial position, without any component making axial contact.

[0009] If the pump's operating point changes, the forces acting on the rotor also change, and the rotor seeks a new equilibrium position by altering the axial position of the impeller and rotor. The gap width at the axial sealing gap changes accordingly. The axial sealing gap thus has a self-regulating function and can therefore be described as a control gap. The gap width at the axial throttling gap automatically adjusts itself so that the rotor is in an axially stable equilibrium position.

[0010] The arrangement of the gap according to the invention not only has the advantage of reducing axial forces. It also ensures that there is no unstable state over the entire operating range in which the rotor moves into a position where the control gap loses its control function.

[0011] In one embodiment, the partition wall projection can completely encircle the first annular wall. By completely encircling the wall, the radial sealing gap can be positioned as far radially outward as possible on the outer diameter of the impeller without having to increase the impeller diameter.

[0012] The partition's projection can be suitably formed by an annular outer section projecting from an annular inner space, creating a step. This step increases the partition's rigidity. In the case of a metallic partition, this step can be produced, for example, by deep drawing or embossing.

[0013] To minimize the flow through the wheel side chamber, the radial throttle gap can be sealed by a sealing ring. For example, such a sealing ring can be held against the partition wall, particularly at its projection, and bear radially against the first annular wall, especially its radial outer surface. The sealing ring can, for example, be a flat gasket.

[0014] Preferably, the first and / or second annular wall is / are formed integrally with the support disc, for example, injection-molded together with it. This simplifies the manufacture of the relief system according to the invention.

[0015] In one embodiment, the relief bore can be formed in the impeller. This makes the relief bore easy to manufacture. Alternatively or additionally, it is possible to form one or more relief bores in the shaft, in which case the shaft is a hollow shaft open towards the suction side of the impeller. The relief bore then extends radially through the wall of the hollow shaft. It should be noted that two or more relief bores are also possible, particularly distributed equidistantly around the circumference of the impeller and / or the hollow shaft.

[0016] It is advantageous if the end face of the second wall facing the partition is conical, so that the width of the axial sealing gap changes in the radial direction, i.e., becomes narrower or wider. Such a conical geometry of the sealing gap reduces the risk of run-on when the sealing gap width becomes very small. In particular, the axial sealing gap can be conical in such a way that it increases with increasing distance from the shaft.

[0017] The second wall can project axially beyond the first wall, in other words, be axially longer. This ensures that, in the case of a partition that is flat in the radial area between the first and second walls, the end face of the first wall facing the partition is significantly further away from the partition than the end face of the second wall facing the partition, and thus the end face of the first wall facing the partition does not form an axial sealing gap.

[0018] Typically, the gap dimensions of the first and second sealing gaps, as well as the neck seal, are less than 1 mm. The axial throttling gap can have a variable width between 0.1 mm and 1.0 mm. Furthermore, the radial throttling gap can have a constant width between 0.05 mm and 1.0 mm, preferably between 0.2 mm and 0.5 mm.

[0019] To prevent contact between rotating and stationary parts due to changes in the operating point of the wet-rotor pump, a magnetic auxiliary bearing can be provided. This bearing can take over axial positioning under low hydraulic forces. In modern, energy-efficient wet-rotor drives, permanent magnets are integrated into the rotor, giving the rotor a magnetic rest position within the stator. This magnetic rest position is characterized by the rotor being symmetrical or centered with respect to its axial position relative to the stator. A magnetic auxiliary bearing can be achieved by ensuring that this rest position is present when the gap width of the variable axial sealing gap is comparatively large, especially at its maximum. This guarantees a defined, contact-free axial rotor position until the pump comes to a standstill. No additional magnetic components are required.

[0020] Further features, advantages and properties of the invention are explained in more detail below with reference to exemplary embodiments. These show: Fig. 1 : a sectional view through the impeller and rotor of a wet rotor pump according to a first design variant Fig. 2 : a sectional view through the impeller and rotor of a wet rotor pump according to a first design variant Fig. 3 : a sectional view through the impeller and rotor of a wet rotor pump according to a first design variant Fig. 4 : a diagram with three sectional views of a wet rotor pump with different axial positions of the impeller

[0021] Figure 1Figure 1 shows a section of a centrifugal pump according to a first embodiment of the invention, in the form of a wet rotor pump 1, in a sectional view along an axial plane through the pump motor axis 26. The wet rotor pump 1 has a permanent magnet rotor 2, which is mounted non-rotatably on a shaft 3. The shaft 3 is supported in a front and a rear radial plain bearing 27, 28. An impeller 7 is arranged in a pump chamber 4, which is enclosed by a pump housing 31 and is delimited from the rotor 2 and the rotor space by a partition 5. The impeller 7 is connected to one end of the shaft 3 by its hub 24 in a non-rotatable manner. Due to the absence of a thrust bearing, the assembly formed by the rotor 2, shaft 3, and impeller 7 is axially displaceable, as indicated by the double arrow shown inside the shaft 3.

[0022] The impeller 7 is a so-called covered impeller. Accordingly, it comprises a support disc 8, a cover disc 10, and blades 9 arranged between them. The cover disc 10 has a central opening 29, the so-called suction inlet 29, which is bounded radially outwards by a tubular section 30 of the cover disc 10, which is generally referred to as the suction neck 30. The space within, in front of, and immediately behind the suction inlet 29 forms the suction side 20 of the impeller 7. In contrast, the periphery and the space radially in front of the impeller 7 form its discharge side 21. The pump housing 31 has a suction opening 22 leading into the pump chamber 4 and a discharge opening 23 leading out of the pump chamber. The impeller 7 extends with its suction neck 30 into the suction opening 22 such that a radial sealing gap exists between the outside of the suction neck 30 and the inside of the suction opening 22.This sealing gap forms a suction neck seal 11 to prevent a hydraulic short circuit between the suction side 20 and the pressure side 21 of the impeller 7. In other words, the suction neck 30 is radially sealed by means of the suction neck seal 11.

[0023] A first annular wall 12 projects from the support disc 8, forming a radial throttling gap 13 together with an annular projection 6 of the partition wall 5 extending in the axial direction. The projection 6 has a larger diameter than the first wall 12 and surrounds it on its outer circumference. This radial gap 13 is thus axially permeable and is, in fact, axially permeable during operation of the wet rotor pump 1. Furthermore, it has a constant gap width, more precisely, a gap width that is independent of the axial position of the impeller 7.

[0024] In addition to the first wall 12, the impeller 7 has a second, annular wall 14 projecting from the support disc 8 to the partition 5. This annular wall divides the impeller side space between the first wall 12 and the shaft 3 into a radially outer annular space 16 and a radially inner annular space 17. In other words, the second wall 14, relative to the pump-motor axis 26, lies on a smaller diameter of the impeller 7 than the first wall 12. The second wall 14 projects axially beyond the first wall 12, so that an axial throttling gap 15 is formed between the end face 25 of the second wall 14 and the partition 5. This axial gap 15 is thus radially permeable and is, in fact, radially permeable during operation of the wet rotor pump 1. Furthermore, its gap width depends on the axial position of the impeller 2. The first and second walls 12, 14 are integrally formed with the support disc 8.

[0025] The suction neck seal 11, more precisely the sealing gap between the suction neck 30 and the pump housing 31, lies on a diameter between the radial throttling gap 13 and the axial throttling gap 15 with respect to the pump motor shaft 26. This ensures that the axial throttling gap functions as a control gap. If the sealing gap between the suction neck 30 and the pump housing 31 were located radially further outward than the radial throttling gap 13, thrust reversal could not be achieved and the control gap would not close. The control principle would then not function. Conversely, if the sealing gap between the suction neck 30 and the pump housing 31 were located radially further inward than the axial throttling gap 13, the axial thrust could not be fully compensated. Due to the upstream axial thrust reversal, the impeller 7 would then collide with the partition 5 on its rear side, so that the first wall 12 and this partition 5 would form a classic axial bearing and there would no longer be a control gap.

[0026] Furthermore, the impeller 7 has a relief bore 18, which forms a fluid connection between the suction side 20 of the impeller 7 and the impeller side chamber located between the support disc 8 and the partition 5. This connection is located at a point in the impeller 7 closer to the shaft 3 than the axial sealing gap 15, so that the relief bore 18 opens into the radially inner annular space 17. As a result of this relief bore 18, a negative pressure is generated in the radially inner annular space 17 during operation of the wet rotor pump 1. This negative pressure leads to a flow through the impeller side chamber, more precisely, a flow from the pressure side 21 of the impeller 7 through the radial throttling gap 13 into the radially outer annular space 16, from there through the axial throttling gap 15 into the radially inner annular space 17, and from there through the relief bore 18 to the impeller suction side.

[0027] The gap width at the axial throttling gap 15 adjusts automatically so that the rotor 2 and the impeller 7 are in an axially stable equilibrium position. If the operating point of the pump 1 changes, the forces acting on the rotor 2 also change, and the rotor 2 seeks a new equilibrium position by changing the axial position of the shaft 3 or the impeller 7 and the rotor 2. The gap width at the axial sealing gap 15 changes accordingly. The axial sealing gap 15 thus adjusts itself. Therefore, it is possible to dispense with an axial bearing in the wet rotor pump 1. The wet rotor pump 1 according to Figure 1 It is therefore without axial bearings.

[0028] The version variant in Figure 2This version differs from the first version only in that the radial throttling gap 13 is sealed by a sealing ring 19. This reduces the gap width of the radial throttling gap 13. This narrower gap 13 has two main effects. On the one hand, leakage is reduced, thereby increasing efficiency. On the other hand, the throttling effect at the gap 13 increases, and the pressure conditions change. This gives the pump designer an additional degree of freedom in positioning the gap, which may be limited, for example, by installation space constraints. The sealing ring 19 is radially movable within a cage with a U-shaped profile in axial section, which allows for narrower gap dimensions. The cage is attached to the partition 5, more precisely at the transition of the projection 6 into an annular section of the partition 5.

[0029] A similar sealing ring is part of the suction neck seal 11. This sealing ring is also held radially movable in a cage with a U-shaped profile in axial section, which is attached to the pump housing 31, more precisely at the transition from the suction opening 22 to the pump chamber 4. This also serves to limit the axial flow through the radial sealing gap at the suction neck 30 to a minimum in order to minimize hydraulic losses.

[0030] Although the design variants in Figure 2 and Figure 3 Each comprising two sealing rings, the wet rotor pump 1 in one embodiment may have a sealing ring only in the suction neck seal 11 or, according to an embodiment not covered by the claimed invention, a sealing ring only at the axial sealing gap 13.

[0031] Furthermore, in an embodiment not shown, the relief bore or an additional relief bore can be present in the shaft 3, more precisely forming a transverse bore in the wall of the hollow shaft 3, so that the flow path extends from the radially inner annular space 17 through the relief bore and the hollow shaft 3 to the suction side 20 of the impeller. The embodiment in Figure 3 differs from the second embodiment only in that the end face 25 of the second wall 14 facing the partition 5 is conical, in particular such that the axial throttling gap 15 becomes larger with increasing distance to the shaft 3.

[0032] In the illustrated embodiments, the axial throttle gap 15 has a variable gap width between 0.1 mm and 1.5 mm, whereby a sealing gap width of less than 1 mm is always present in the operating state, and larger gap widths are only possible when the unit is stationary. In contrast, the radial throttle gap 13 and the sealing gap at the suction neck seal each have a constant gap width between 0.05 mm (sealing ring) and 0.5 mm (sealing gap).

[0033] Figure 4 The upper section shows a diagram illustrating the axial force F_ax,res resulting from all individual forces as a function of the axial rotor position or the gap width s_gap,hub,2 of the axial throttle gap 15 at a constant pump operating point (flow rate, delivery head, pump speed), where the rotor positions 1, 2 and 3 marked in the diagram are shown in the three sectional views in the lower section. Figure 4The diagrams are shown. The cross-sectional image at the bottom left shows rotor position 1 with a large axial gap 15, the cross-sectional image at the bottom center shows rotor position 2 with a medium axial gap 15, and the cross-sectional image at the bottom right shows rotor position 3 with a minimal axial gap 15. Reference symbols are omitted for clarity. Figure 4 largely omitted.

[0034] A magnetic auxiliary bearing, enabled by the permanent magnet rotor 2, is achieved when the wet rotor pump 1 is designed such that the rotor 2 is in its magnetic rest position when the rotor 1 is in position 1. This magnetic rest position exists when the gap width of the axial throttle gap 15 is comparatively large, here approximately 0.7 mm. The magnetic rest position is understood to be an axially approximately centered position of the rotor 2 relative to the stator when the pump is not in operation.

[0035] By definition, the positive force direction points towards the pump housing 31, see rotor position 3 in Figure 4 bottom right, i.e., against the direction of inflow into pump chamber 4.

[0036] If the impeller 7 is located far away from the partition 5 (rotor position 1, Figure 4 (bottom left), the low pressure level in the wheel side space between impeller 7 and partition 5 (grey dashed line) causes a resultant force F_ax,res, which displaces the rotor 2 towards the partition 5 and closes the axial throttle gap 15. At a gap width of approximately 0.3 mm at the axial throttle gap 15, the impeller 7 reaches an equilibrium position (rotor position 2, Figure 4 bottom center). If the impeller 7 is very close to the partition 5 (rotor position 3, Figure 4(bottom right), the high pressure level in the wheel side space (black dashed line) causes a resultant force F_ax,res, which displaces the rotor 2 towards the pump housing 31 and reopens the axial throttle gap 15. In the case shown, the rotor finds its equilibrium position (position 2) at a gap width of approximately 0.3 mm, where the resultant axial forces cancel each other out.

[0037] This automatic adjustment of the impeller or rotor position, and thus also of the gap width s_gap,hub,2, eliminates the need for an axial bearing. Consequently, the wet rotor pump 1 shown in the figures is designed without an axial bearing. This offers numerous advantages: Axial bearing losses are eliminated and efficiency is increased. There is no axial bearing wear, no need for maintenance / replacement of an axial bearing, and for EEI (Energy Efficiency Index) measurements of wet rotor pumps 1, no run-in effects at the axial bearing need to be considered. Furthermore, axial thrust reversal does not need to be taken into account. Depending on the pump type, even two axial bearing positions can be eliminated. By eliminating the axial bearing(s), a cost reduction and a reduction in installation space are achieved. Since the rotor 2, as a wet rotor with permanent magnets, has a neutral magnetic position axially, it can be positioned axially by the magnetic forces so that there is no contact with the housing when stationary. This prevents the impeller 7 from colliding either with the pump housing 31 on the left or with the partition 5 on the right. Ideally, the rotor is always within these limits and never on either boundary.This results in optimized start-up behavior without sticking. An axial emergency running bearing is not necessary. Thus, the only desired contact between rotating and stationary parts is found in the radial plain bearings. Compared to impellers that only have a relief bore, the volumetric losses in the solution according to the invention are reduced due to the additional axial throttling gap 15 with a very small gap width. Compared to non-relieved impellers, the relief bore(s) 18 achieves the removal of particles from the impeller side space and thus rotor chamber protection. The radial throttling gap 13 in . Fig. 1 It has a supporting effect, as it acts radially as an additional hydrodynamic bearing, supporting and damping the rotor and thus relieving the radial bearings. In the variant with a narrow gap ( Figs. 2 and 3However, this does not apply, as the sealing ring 19 is radially movable there. The integration of the pressure relief system into the impeller contour (first and second walls 12, 14 are integral, in particular one piece with the impeller 7) results in a compact design.

[0038] It should be noted that the foregoing description is given merely as an example for illustrative purposes and in no way limits the scope of protection of the invention. Features of the invention that are indicated as "may", "exemplary", "preferred", "optional", "ideal", "advantageous", "if applicable", "suitable" or the like are to be considered purely optional and likewise do not limit the scope of protection, which is exclusively defined by the claims.

[0039] Although the foregoing description of the invention mentions a multitude of physical, intangible, or process-related features relating to one or more specific embodiments, these features can also be used in isolation from the specific embodiment, at least insofar as they do not necessarily require the presence of further features. Conversely, these features mentioned in relation to one or more specific embodiments can be combined arbitrarily with one another and with further disclosed or undisclosed features of illustrated or unillustrated embodiments, at least insofar as the features do not mutually exclude each other or lead to technical incompatibilities. Reference symbol list

[0040] 1 Wet rotor pump 2 Rotor 3 Shaft 4 Pump chamber 5 Partition 6 Projection 7 Impeller 8 Support disc 9 Blades 10 Cover plate 11 Suction neck seal 12 First wall 13 Radial throttle gap 14 Second wall 15 Axial throttle gap 16 Outer annular space 17 Inner annular space 18 Relief bore 19 Sealing ring 20 Suction side of impeller 21 Pressure side of impeller 22 Suction opening 23 Pressure opening 24 Hub 25 End face 26 Pump motor shaft 27 Front plain bearing 28 Rear plain bearing 29 Suction inlet 30 Suction neck 31 Pump housing

Claims

1. Wet rotor pump (1) with a permanent magnet rotor (2) and a pump chamber (4) which is delimited towards the rotor (2) by a separating wall (5) and in which an impeller (7) is arranged that is mounted on an axially moveable shaft (3) with a torque-proof connection and has a support plate (8), a cover plate (10) and vanes (9) arranged between these, wherein the cover plate (10) is radially sealed by means of a suction neck seal (11) and a first annular wall (12) projects from the support plate (8) that, jointly with an axial projection (6) of the separating wall (5), forms a radial throttle gap (13) with a constant gap width that permits axial flow, and wherein a relief bore (18) forms a fluid connection between the suction side (20) of the impeller (2) and an impeller's side space lying between the support plate (8) and the separating wall (5), wherein the wet rotor pump, instead of an axial bearing, the impeller (7) has a second annular wall (14) that extends to the separating wall (5) and that divides the impeller's side space between the first wall (12) and the shaft (3) into a radial outer annular space (16) and a radial inner annular space (17) and that forms, together with the separating wall (5), an axial throttle gap (15) that depends on the axial position of the impeller (7) and that permits radial flow, wherein the suction neck seal (11) lies on a diameter between the radial throttle gap (13) and the axial throttle gap (15) and the relief bore (18) opens into the radial inner annular space (17).

2. Wet rotor pump (1) according to claim 1, characterised in that the projection (6) of the separating wall (5) encompasses the outer circumference of the first annular wall (12).

3. Wet rotor pump (1) according to claim 1 or 2, characterised in that the radial throttle gap (13) is sealed by a sealing ring (19).

4. Wet rotor pump (1) according to one of the preceding claims, characterised in that the first and / or second annular wall (12, 14) is formed in once piece with the support plate (8).

5. Wet rotor pump (1) according to one of the preceding claims, characterised in that the relief bore (18) is formed in the impeller (7).

6. Wet rotor pump (1) according to one of the preceding claims, characterised in that the shaft (3) is a hollow shaft open towards the suction side (20) and the relief bore (18) is formed in the shaft (3).

7. Wet rotor pump (1) according to one of the preceding claims, characterised in that the end face (25) of the second wall (14) facing towards the separating wall (5) is conical, in particular so that the axial throttle gap (15) becomes larger as the distance to the shaft (3) increases.

8. Wet rotor pump (1) according to one of the preceding claims, characterised in that the second wall (14) projects axially compared to the first wall (12).

9. Wet rotor pump (1) according to one of the preceding claims, characterised in that the axial throttle gap (15) has a variable gap width between 0.1 mm and 1.00 mm.

10. Wet rotor pump (1) according to one of the preceding claims, characterised in that the radial throttle gap (13) has a constant gap width between 0.05 mm and 1.0 mm, preferably between 0.2 mm and 0.5 mm.

11. Wet rotor pump (1) according to one of the preceding claims, characterised in that is comprises a magnetic auxiliary bearing.

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