Centrifugal pump having a device

Abstract

The invention relates to a centrifugal pump having at least one impeller (4, 7, 8) which sits on a drive shaft (14). The drive shaft (14) is supported by a device (18) which comprises at least one media-lubricated plain bearing, wherein the plain bearing comprises an inner arrangement (20) which is connected to the drive shaft (14) for conjoint rotation and comprises an outer arrangement (21) which is positioned in a stationary manner in the suction housing (4). A gap is formed between the inner arrangement (20) and the outer arrangement (21). The outer arrangement (21) has an element with a cylindrical inner face (22), said element being formed on the basis of at least one polymeric material. The outer arrangement (21) comprises sealing elements (26) for fixing a further element (23).

Description

[0001] 10523A

[0002] KSB SE & Co. KGaA 67227 Frankenthal

[0003] Description

[0004] centrifugal pump with a device

[0005] The invention relates to a centrifugal pump with at least one impeller mounted on a drive shaft, wherein the drive shaft is supported by a device comprising at least one media-lubricated sliding bearing, wherein the sliding bearing comprises an inner arrangement that is rotationally fixed to the drive shaft and an outer arrangement that is stationary in the housing, wherein a gap is formed between the inner arrangement and the outer arrangement, wherein the outer arrangement has an element with a cylindrical inner surface formed on the basis of at least one polymeric material.

[0006] A centrifugal pump with at least one impeller refers in particular to multi-stage centrifugal pumps, for example, in a vertical installation. Centrifugal pumps are described as multi-stage when several impellers are arranged one after the other and the pumped flow passes through them sequentially.

[0007] The delivery head of a single-stage centrifugal pump is primarily determined by the impeller design and the peripheral speed. If the rotational speed cannot be increased further due to external constraints, and increasing the impeller diameter leads to very low specific speeds and thus inefficient efficiencies, the delivery head can be economically increased by arranging several stages in series. With unchanged dimensions and rotational speeds, the flow rate of such a multi-stage pump remains the same, while the power requirement and the delivery head increase proportionally to the number of stages. Each stage consists of an impeller and a guide vane, which usually incorporates recirculation blading.

[0008] Multistage, vertical centrifugal pumps in a modular design are usually mounted on a base plate or designed as a block unit. They typically feature a motor-mounted speed control system and cast radial impellers. Multistage centrifugal pumps are particularly common in supra-regional heating water systems, such as district heating networks, where the pump rotor is supported and mounted by a fluid-lubricated radial bearing.

[0009] Plain bearings are frequently used in centrifugal pumps. In this design, a moving component slides within a stationary component. In radial plain bearings for centrifugal pumps, the rotating component is usually part of the shaft, while the stationary component is a bearing element in the form of a bushing.

[0010] Multi-section centrifugal pumps are frequently equipped with medium-lubricated shaft guide bearings in the form of plain bearings. The choice of material must be particularly careful, as specific properties of the lubricating medium often need to be considered. For water as a lubricating medium, for example, there are several bearing materials with good tribological properties. These include metallic alloys, ceramics, elastomers, hard rubber, electrographitized carbon with and without resin impregnation, and hard carbon with resin or antimontane impregnation.

[0011] EP 0 752 538 A2 discloses a fluid-lubricated plain bearing, particularly in centrifugal pumps, wherein a hard and a soft material serve as sliding partners. The hard partner consists of metal and the soft partner of carbon fiber reinforced carbon.

[0012] If a conveyed medium is contaminated as a bearing lubricant or contains solid components such as sand, the use of hard metals or ceramic materials (e.g. silicon carbide) is recommended according to the state of the art.

[0013] Bearing material. As a rule, the bearing bushings and shaft protection sleeves made of the same material form a maintenance-free plain bearing.

[0014] EP 0204 235 B1 discloses a sliding bearing made of ceramic material for supporting pump shafts, wherein a bearing sleeve rotating with the shaft rotates within a bearing made of the same material and the bearing is elastically mounted within a housing and in particular silicon carbide is used as the bearing material.

[0015] Silicon carbide (SiC) is a widely used material for plain bearing sleeves. However, in certain applications, SiC sleeves can be prone to vibration-induced fractures.

[0016] An alternative to ceramic materials for plain bearing sleeves and bushings are, for example, plastic-based parts for plain bearings. These are also known from the prior art.

[0017] EP 1 335 811 B1 discloses a sliding bearing for a centrifugal pump lubricated by the pumped medium, comprising a stationary part arranged in the housing of the centrifugal pump and a rotating part arranged on the shaft of the centrifugal pump, which interacts with the stationary part in a sliding pair, wherein one part of the sliding pair consists of a composite material, in particular carbon or SiC fibers with a matrix of PEEK, carbon or carbon with SiC, while the other part has a sliding surface made of a hard metallic material, which is supported by a carrier material.

[0018] Especially when using centrifugal pumps in district heating networks, there can be enormous differences or fluctuations in operating parameters between summer and winter operation. These fluctuations can lead to vibrations in the pump's operating mode, meaning that high hardness of the bearing materials alone is insufficient. In particular, the brittleness of hard bearing materials can prove problematic and lead to crumbling plain bearings. At the same time, plastic-based bearing materials alone may not be sufficiently hard or may not exhibit adequate emergency running properties.

[0019] The object of the invention is to provide a centrifugal pump with at least one impeller, the drive shaft of which is supported by a device suitable for use with a wide range of operating parameters. The centrifugal pump should also be able to withstand vibrations caused by fluctuations in the operating parameters without damage. The design of the centrifugal pump should facilitate the replacement of spare parts. The centrifugal pump should be simple and cost-effective to manufacture.

[0020] This problem is solved according to the invention by a centrifugal pump with at least one impeller according to the features of claim 1. Preferred embodiments can be found in the dependent claims, the subclaims, the description and the drawings.

[0021] According to the invention, the outer arrangement comprises sealing elements for fixing a further element.

[0022] The additional element is preferably designed as a bushing holder. Two sealing elements, for example in the form of O-rings, position the additional element.

[0023] In one embodiment of the invention, the bushing holder of the outer arrangement has a bulge that holds two O-rings in position. Advantageously, the O-rings also act as vibration dampers, which can be beneficial during the vibration-prone operation of the centrifugal pump.

[0024] The outer assembly is stationary within the housing of the centrifugal pump, preferably comprises the bushing and a bushing holder, and can be designed, for example, as a one-piece or two-piece assembly. 5 10523A

[0025] The inner arrangement is preferably designed as a sleeve that is rotatably connected to the drive shaft.

[0026] The device is designed, for example, as a media-lubricated sliding bearing, wherein the sliding bearing comprises an inner arrangement and an outer arrangement.

[0027] A sliding bearing gap is preferably formed between the inner and outer arrangements. Under normal operating conditions, this gap is lubricated by the conveyed medium. Particularly during start-up phases and / or operation with highly fluctuating operating parameters and / or under extreme operating conditions, high hardness and wear resistance of the element with a cylindrical inner surface in the outer arrangement, especially the sliding bearing bushing, is advantageous.

[0028] The element with a cylindrical inner surface of the outer arrangement is made of a polymeric material, for example a high-performance plastic.

[0029] A high-performance plastic is a plastic that exhibits exceptional mechanical, thermal, and chemical properties. High-performance plastics can withstand extreme conditions, such as high temperatures, strong chemical influences, and high mechanical stress.

[0030] Surprisingly, the polymeric material of the element with a cylindrical inner surface of the outer arrangement withstands temperatures of more than 300 °C, preferably more than 400 °C, in particular more than 500 °C, and is therefore unexpectedly advantageous for the application of centrifugal pumps in district heating networks.

[0031] Surprisingly, the polymeric material of the element with a cylindrical inner surface of the outer arrangement exhibits a loss factor (tan θ) of more than 0.01 and less than 0.07, preferably more than 0.02 and less than 0.06, particularly more than 0.03 and less than 0.05, at room temperature and advantageously dampens 6 10523A

[0032] Vibrations, especially with a suspended pump rotor in a vertical installation of the centrifugal pump.

[0033] Advantageously, the polymeric material of the element with a cylindrical inner surface of the outer arrangement has a hardness of more than 85 Shore D, preferably more than 95 Shore D, in particular more than 105 Shore D, and is therefore advantageously hard for use in sliding bearings in multi-stage centrifugal pumps.

[0034] In one embodiment of the invention, the element with a cylindrical inner surface of the outer arrangement is made of PEEK. Polyetheretherketone (PEEK) belongs to the group of polyaryletherketones (PAEK), which are a subgroup of thermoplastic high-performance polymers.

[0035] In another variant of the invention, the element with a cylindrical inner surface of the outer arrangement is made of polyetherketone (PEK) or of polyetherketoneketone (PEKK) or of polyetherketoneetherketoneketone (PEKEKK) or of mixtures thereof.

[0036] PEEK can withstand temperatures up to 250 °C without losing its mechanical properties and possesses high tensile and flexural strength as well as stiffness. PEEK is also resistant to a wide range of chemicals, including organic and inorganic acids, alkalis, and organic solvents. Due to its excellent tribological properties, PEEK is ideally suited for plain bearing and sealing applications. Furthermore, PEEK exhibits low thermal expansion and high dimensional stability, making it extremely advantageous for use in centrifugal pumps with fluid-lubricated shaft guide bearings in multi-regional heating water systems.

[0037] Polyetherketoneketone (PEKK) offers similar properties to PEEK, but with a higher glass transition temperature and greater thermal stability. PEKK is highly wear-resistant and chemically resistant, making it ideal for plain bearing applications. 7 10523A

[0038] For use in the sliding bearing according to the invention, for example polyphenylene sulfide (PPS) or polyetherimides (PEI) or polytetrafluoroethylene (PTFE) or mixtures thereof can also exhibit the tribological properties such as low friction and high wear resistance as well as sufficient mechanical strength and temperature resistance for centrifugal pumps with pumped medium-lubricated shaft guide bearings in supra-regional heating water systems.

[0039] In addition to these materials, composite materials that combine these polymers with fillers such as glass fibers, carbon fibers or PTFE can also be used to further improve the sliding and wear properties for plain bearings in centrifugal pumps.

[0040] In one variant of the invention, the element with a cylindrical inner surface of the outer arrangement exhibits a damping in the form of the loss factor (tan θ) of more than 0.025 and simultaneously a hardness of more than 85 Shore D.

[0041] The loss factor (tan θ) is a measure of a material's damping properties. It defines the ratio between the loss modulus and the storage modulus. A high loss factor means the material is good at converting mechanical energy into heat and damping vibrations, while a low loss factor means the material stores and releases the most energy.

[0042] For example, the element with a cylindrical inner surface of the outer arrangement in the PEEK version has a loss factor in the range of 0.01 to 0.03 at room temperature.

[0043] In one embodiment of the invention, the element with a cylindrical inner surface of the outer arrangement, when made of PEKK, exhibits a loss factor in the range of 0.02 to 0.05 at room temperature. 8 10523A

[0044] For example, the element with a cylindrical inner surface of the outer arrangement in the PPS version has a loss factor in the range of 0.01 to 0.03 at room temperature.

[0045] In another variant of the invention, the element with a cylindrical inner surface of the outer arrangement in the PEI embodiment has a loss factor in the range of 0.02 to 0.05 at room temperature.

[0046] In the Rockwell hardness test, a ball or diamond indenter is pressed onto the surface of the material and the depth of penetration is measured. The measured depth is then used to determine the Rockwell hardness.

[0047] In Shore hardness measurement, a sample with a smooth surface and a minimum thickness of 6 mm is subjected to a perpendicular load with the pressure foot at a standard room temperature of 23 ± 2 °C, and the hardness value is read after typically 15 seconds.

[0048] For example, the element with a cylindrical inner surface of the outer arrangement in the PEEK version has a Rockwell hardness according to ASTM D785 or ISO 2039-2 of more than 99 and / or less than 107 HR or a Shore hardness according to ASTM D2240 or ISO 868 of more than 85 and / or less than 95 Shore D.

[0049] In one variant of the invention, the element with a cylindrical inner surface of the outer arrangement in the PEKK version has a Shore hardness according to ASTM D2240 or ISO 868 of more than 87 and / or less than 97 Shore D.

[0050] For example, the element with a cylindrical inner surface in the outer arrangement, when made of PPS, has a Shore hardness according to ASTM D2240 or ISO 868 of more than 80 and / or less than 90 Shore D. 9 10523A

[0051] In a further variant of the invention, the element with a cylindrical inner surface of the outer arrangement in the PEI version has a Shore hardness according to ASTM D2240 or ISO 868 of more than 85 and / or less than 90 Shore D.

[0052] For example, the outer arrangement features at least one integrated lubricating element made of graphite. In one design variant, the graphite-based lubricant can be incorporated as a powder into the matrix of the high-performance plastic. High wear resistance alone is often insufficient for plain bearings. A bushing with a large number of evenly distributed lubricating elements, in particular, achieves emergency running properties through integrated emergency lubrication.

[0053] In one embodiment, the outer arrangement has at least a proportion of lubricating element in the form of powdered graphite of more than 3 wt.%, preferably more than 10 wt.%, in particular more than 15 wt.%, which is integrated into the polymer matrix of the high-performance plastic.

[0054] The advantage of graphite in plain bearings lies in its ability to act as a dry lubricant. Using graphite in plain bearings offers the benefits of uniform lubrication, low friction, and reduced wear, without the need for external lubrication.

[0055] The integrated lubricating elements ensure the emergency running capability of the device before the media lubrication can take effect and / or if the media lubrication cannot be permanently and completely ensured, for example due to cavitation in the centrifugal pump.

[0056] For example, the other element, in its version as a bushing holder, is made of chrome steel and is therefore particularly robust and wear-resistant. 10 10523A

[0057] In one embodiment of the invention, the inner arrangement is made of a steel material.

[0058] For example, the internal structure is made of chromium steel and is therefore particularly robust and wear-resistant.

[0059] In an advantageous embodiment of the invention, the inner arrangement is made of a martensitic steel, for example 1.4021 or 1.4057.

[0060] In another variant of the invention, the inner arrangement is made of a precipitation-hardened steel, for example 1.4022.

[0061] In an alternative version of the invention, the inner arrangement is made of a heat-treated steel, for example a 1.7225.

[0062] In a preferred embodiment of the invention, the inner arrangement comprises a carbon layer. A thin carbon layer is characterized in particular by its extreme hardness.

[0063] For example, the carbon layer is formed from a ta-C and / or an aC:H and / or an sp3-hybridized CVD layer.

[0064] Carbon layers are defined as layers in which carbon is the predominant component. The carbon layer can be applied using, for example, PVD (Physical Vapor Deposition), physical vapor deposition (such as by evaporation or sputtering), or CVD (Chemical Vapor Deposition) processes.

[0065] For example, it is an amorphous carbon layer, in particular a tetrahedral hydrogen-free amorphous carbon layer, also known as a ta-C layer. The atomic bonds belonging to the crystal lattice of graphite (three in total) are sp² hybridizations. 11 10523A

[0066] In a diamond layer, each carbon atom forms a tetrahedral arrangement with four neighboring atoms. This arrangement results in very small atomic distances and high bonding forces in all spatial directions, which explains the high strength and extreme hardness of diamond. The atomic bonds in the diamond crystal lattice (four in total) are called sp3 hybridizations.

[0067] A particularly advantageous embodiment of the invention consists of a carbon layer containing a mixture of sp3- and sp2-hybridized carbon. This layer is characterized by an amorphous structure into which foreign atoms such as hydrogen, silicon, tungsten, or fluorine may also be incorporated.

[0068] The carbon layer is preferably formed as a hydrogen-containing amorphous carbon layer, which is generally referred to as aC:H.

[0069] The carbon layer can additionally contain metallic and / or non-metallic doping. Generally, metal-containing carbon layers are designated aC:H:Me. The metal Me can be, for example, tungsten, titanium, silicon, or tantalum. With tungsten as the dopant, the designation is aC:H:W. A coating containing a non-metal, designated aC:H:X, where X represents a non-metal, can also be used.

[0070] Preferably, the carbon layer is formed as an aC:H coating. Compared to the ta-C coating, the aC:H coating can be formed even smoother, although somewhat softer, while still possessing enormous hardness.

[0071] The carbon coating exhibits a very low coefficient of friction combined with excellent chemical resistance. The coating's hardness is very close to that of diamonds, with the hardness in the aC:H version being greater than 15 GPa and / or less than 25 GPa. 12 10523A

[0072] For example, the hardness of the carbon layer in the ta-C version is more than 40 GPa, and / or less than 75 GPa.

[0073] In one embodiment of the invention, the carbon layer is applied as a coating to the outer surface of the inner arrangement in the form of a sleeve. The thickness of the layer is advantageously more than 0.5 pm, preferably more than 1.0 pm, and particularly more than 1.5 pm. Furthermore, it is advantageous if the carbon layer is less than 18 pm, preferably less than 16 pm, and particularly less than 14 pm.

[0074] Ideally, the carbon coating has an extremely smooth surface with non-stick properties, where the average roughness value R a the thickness of the carbon layer is less than 0.3 pm, preferably less than 0.2 pm, and in particular less than 0.1 pm.

[0075] Especially when the centrifugal pump is operated under fluctuating and / or extreme operating conditions, the carbon layer of the inner assembly is subjected to enormous stress. Surprisingly, it has proven advantageous to place a CrN layer between the carbon layer and the chromium steel of the inner assembly.

[0076] Chromium nitride coatings are frequently applied to metallic surfaces to improve their service life and performance. These coatings can be thin, allowing for precise control of the material properties. They are typically produced by thermal processes such as plasma nitriding or gas nitriding. Chromium nitride coatings have been proven to increase the hardness, corrosion resistance, and wear resistance of the material.

[0077] In one embodiment of the invention, the thickness of the CrN layer is 1 pm and can, for example, prevent spalling of the aC:H layer under extreme operating conditions of the centrifugal pump. 13 10523A

[0078] For example, the plain bearing is located in the suction area of ​​the centrifugal pump. It supports and mounts the pump rotor with its multiple impellers on the side of the centrifugal pump facing away from the motor.

[0079] Ideally, the device is positioned at the lowest bearing point when the centrifugal pump is mounted vertically. The device effectively dampens vibrations of the suspended impeller, particularly during undesirable operating behavior of the centrifugal pump, and simultaneously offers not only advantageous hardness but also remarkable emergency running properties and good resistance to high temperatures. Unlike previously known devices based on ceramic materials such as SiC, this device does not exhibit the risk of breakage.

[0080] For example, the invention comprises a medium-lubricated plain bearing with a tribological pairing of a carbon layer on a chromium steel sleeve against a bushing made of a polymeric material, in particular a high-performance plastic such as PEEK or PEKK. The carbon coating reduces the coefficient of friction of the bearing pairing and leads to higher durability of the coated sleeve.

[0081] The substrate of the coated sliding component is, for example, a stainless steel, such as a 13% chromium steel, an austenitic-feminine duplex steel or a nickel-based alloy.

[0082] For example, the hardness of the aC:H coating is 25 GPa, which corresponds to approximately 2500 HV.

[0083] By replacing the otherwise standard SiC or graphite bushings with a bushing made of a high-performance plastic, the bushing and bushing holder can, for example, be manufactured as a single piece. This reduces the number of parts and the assembly effort. Furthermore, the bushing made of a high-performance plastic is vibration-damping, significantly less brittle, and therefore less susceptible to breakage. 14 10523A

[0084] Further features and advantages of the invention will become apparent from the description of exemplary embodiments with reference to the drawings and from the drawings themselves.

[0085] This shows:

[0086] Fig. 1 shows a sectional view of an exemplary centrifugal pump,

[0087] Fig. 2 shows a detailed sectional view of the device.

[0088] Fig. 1 shows a sectional view of an exemplary centrifugal pump. The multi-stage centrifugal pump is designed with a radial flow inlet 1 and a radial flow outlet 2. The hydraulics of the centrifugal pump have a bearing and are connected to the motor (not shown) via a shaft coupling.

[0089] The pumped medium enters the centrifugal pump via the suction casing 3 and is accelerated outwards by the suction impeller 4. In the flow contour of the stage casing 5, the kinetic energy of the pumped medium is converted into pressure energy, and the pumped medium is guided via the guide vane 6 to the next impeller 7. This process is repeated through all stages until the last impeller 8, and is then directed via the discharge casing 9 to the discharge flange 10, through which it exits the centrifugal pump.

[0090] The backflow of the pumped medium from the stage housing 5 into the suction area of ​​the preceding impeller 4, 7 is prevented by a throttle gap 11. A relief piston 12 may be located on the rear side of the last impeller 8, via which axial thrust compensation is achieved by hydraulic forces. The hydraulic system is limited on the rear side of the last impeller 8 and the relief piston 12 by a sealing housing 13, through which the drive shaft 14 passes. The shaft passage 15 through the sealing housing 13 is sealed against the environment by a dynamic shaft seal 16. 15 10523A

[0091] The drive shaft 14 is supported by rolling bearings 17 and a device 18 in the form of a plain bearing, which are received by a bearing housing 19 and the suction housing, respectively. The bearing housing 19 is connected to the suction housing 3.

[0092] Figure 2 shows a detailed sectional view of the device 18. The device 18 is designed as a media-lubricated sliding bearing, the sliding bearing comprising an inner arrangement 20 and an outer arrangement 21.

[0093] The inner assembly 20 is designed as a sleeve made of 13% chromium steel, in the illustrated embodiment 1.4021, and is rotationally fixed to the drive shaft 14. The outer assembly 21 is stationary in the suction housing 3 of the centrifugal pump and comprises an element with a cylindrical inner surface 22 in the form of a bushing, and a further element 23 in the form of a bushing holder, in the two-part embodiment. The gap 24 of the sliding bearing is formed between the inner assembly 20 and the outer assembly 21.

[0094] The bushing holder of the outer arrangement 21 has a curvature 25 and holds two sealing elements 26 in the form of O-rings in position. The O-rings also act as vibration dampers.

[0095] The bushing of the outer arrangement 21 has a damping in the form of the loss factor (tan θ) of 0.05 and simultaneously a hardness of 95 Shore D and is made of PEKK in the illustrated embodiment.

[0096] The chromium steel sleeve of the inner arrangement 20 has a CrN layer 27 with a thickness of 1 pm. A carbon layer 28 in the form of an aC:H coating is applied to the CrN layer 27. The thickness of the aC:H coating is 5 pm and the hardness of the aC:H coating is 25 GPa. The average roughness value R a The thickness of the aC:H coating is 0.15 pm. 16 10523A

[0097] Under normal operating conditions, the gap 24 of the sliding bearing is lubricated by the pumped medium. Particularly during start-up phases and / or operation with highly fluctuating operating parameters and / or operation under extreme operating parameters, the high hardness and thus the wear resistance of the sliding bearing bushing, in combination with the smooth hardness of the sliding bearing sleeve and the emergency lubricating graphite powder elements embedded in the polymer matrix within the bushing, ensures trouble-free and long-lasting operation of the centrifugal pump.

[0098] 17 10523A

[0099] Reference symbol list

[0100] 1 Radial flow inlet 16 Shaft seal

[0101] 2 Radial flow outlet 17 Rolling bearings

[0102] 3 Suction housings 18 Device

[0103] 4 suction impeller 19 bearing housing

[0104] 5-stage housing 20 Internal arrangement

[0105] 6 Guide wheel 21 Outer arrangement

[0106] 7 Impeller 22 Element with cylindrical inner surface

[0107] 8 Last wheel 23 Further element

[0108] 9 pressure housings 24 gaps

[0109] 10 Pressure flange 25 Curvature

[0110] 11 Throttle gap 26 Sealing elements

[0111] 12 relief pistons, 27 CrN layer

[0112] 13 Sealing housing 28 Carbon layer

[0113] 14 Drive shaft

[0114] 15 Shaft feedthrough

Claims

18 10523A Patent claims centrifugal pump with a device 1. Centrifugal pump with at least one impeller (4, 7, 8) mounted on a drive shaft (14), wherein the drive shaft (14) is supported by a device (18) comprising at least one media-lubricated sliding bearing, wherein the sliding bearing comprises an inner arrangement (20) which is rotationally fixed to the drive shaft (14) and an outer arrangement (21) which is stationary in the suction housing (3), wherein a gap (24) is formed between the inner arrangement (20) and the outer arrangement (21), wherein the outer arrangement (21) has an element with a cylindrical inner surface (22) which is formed on the basis of at least one polymeric material, characterized in that the outer arrangement (21) comprises sealing elements (26) for fixing a further element (23).

2. Centrifugal pump according to claim 1, characterized in that the element (22) has a damping in the form of the loss factor (tan θ) of more than 0.025 and simultaneously a hardness of more than 85 Shore D.

3. Centrifugal pump according to claim 1 or 2, characterized in that the outer arrangement (21) has at least a proportion of lubricating element of more than 3 wt.%, preferably of more than 10 wt.%, in particular of more than 15 wt.%, wherein the lubricating element is preferably made of graphite. 19 10523A 4. Centrifugal pump according to one of claims 1 to 3, characterized in that the further element (23) is made of chromium steel.

5. Centrifugal pump according to one of claims 1 to 4, characterized in that the outer arrangement (21) is formed in one piece.

6. Centrifugal pump according to one of claims 1 to 5, characterized in that the inner arrangement (20) is made of chromium steel.

7. Centrifugal pump according to one of claims 1 to 6, characterized in that the inner arrangement (20) has a carbon layer (28).

8. Centrifugal pump according to claim 7, characterized in that the carbon layer (28) consists of a ta-C and / or an aC:H and / or an sp 3 -hybridized CVD layer is formed.

9. Centrifugal pump according to claim 7 or 8, characterized in that a CrN layer (27) is arranged between the carbon layer (28) and the chromium steel of the inner arrangement (20).

10. Centrifugal pump according to one of claims 1 to 9, characterized in that the device (18) is arranged in the suction area, in particular in the lowest bearing point, when the centrifugal pump is installed vertically.

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