Abstract:
A multistage centrifugal pump ( 1 ) has impellers ( 9 ) arranged on a common shaft ( 8 ), which is rotatably arranged within a pump casing ( 2 - 4 ). One end of the shaft ( 8 ) is led out of the casing ( 2 - 4 ) for connection to a drive motor and another shaft end ( 15 ) is rotatably mounted in the pump casing ( 2 - 4 ). The shaft end ( 15 ) which is mounted within the pump casing ( 2 - 4 ) is subjected to a counter-force which is produced by way of pressure subjection via a conduit connection to a delivery side of the pump. An axial seal ( 11 ) is provided on the shaft end ( 15 ) arranged within the pump casing ( 2 - 4 ). The rotating part of the axial seal is led on the shaft end and the non-rotating part is led, axially movably, within the pump casing ( 2 - 4 ). A sealing arrangement is provided between the pump casing and the axially movably mounted part.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119 of European Application 15 195 416.1 filed Nov. 19, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to a multi-stage centrifugal pump with which the impellers of the pump stages are arranged on a shaft which is rotatably arranged within a pump casing and which at one end is led out of the casing for connection to a drive motor and at the other end is arranged within the pump casing. 
       BACKGROUND OF THE INVENTION 
       [0003]    With multi-stage centrifugal pumps, with which the impellers of the pump stages are arranged on a common shaft and are rotatably arranged within a pump casing, the drive is often effected via an external motor which is drivingly connected to the pump shaft by a coupling and is received and fastened on a motor stool, which is to say a casing part which is designed for receiving the motor. For this, the one shaft end is sealingly led through the pump casing and out of this, and the other shaft end is mounted within the pump casing. Thereby, it is counted as belonging to the state of the art to accommodate the forces acting upon the pump shaft by way of the motor bearings and to merely provide a radial guiding, for example by way of shaft sleeves which are arranged in the region of the pump stages, within the pump casing. In contrast, the pump-side shaft end is mounted radially and/or axially within the pump casing, in order to relieve the motor bearings, in the case of larger multi-stage pumps. Common to all designs however is an increased loading and thus an increased wear of the motor bearings. 
         [0004]    Thereby, it is counted as belonging to the state of the art, to compensate these axial forces upon the shaft which result due to the hydraulic forces, be it by way of subjecting the shaft end mounted in the casing to the pressure of the delivery side or by way of the provision of recesses in the shrouds of the impellers. The latter results in a significant loss in the efficiency, on account of the backflows which are caused by way of this. With hydraulic force compensation, there exists the problem that a highly-loaded seal is to be provided between the rotating shaft end and the stationary casing, which, if it has a good sealing effect, creates a high friction and thus also a high wear and leads to overflow losses given the degradation of the sealing effect. 
       SUMMARY OF THE INVENTION 
       [0005]    Against this state of the art, it is an object of the present invention, to design a multi-stage centrifugal pump of the known type, such that on the one hand the hydraulically caused forces upon the shaft can be reduced, but on the other hand a good, low-friction and low-wear sealing, which is therefore stable over the long term, is effected. 
         [0006]    With the multi-stage centrifugal pump according to the invention, the impellers of the pump stages are arranged on a shaft in a direct manner or via a carrier body, said shaft being rotatably arranged within a pump casing. This shaft, at one end, is led out of the casing in a sealed manner for connection to a drive motor and at the other end this shaft is arranged within the pump casing. The shaft end arranged within the pump casing is subjected to a counter-force which is produced by way of pressure subjection via a conduit connection to a delivery side of the pump, typically, but not necessarily to the pressure of the last pump stage, thus the delivery side of the pump. According to the invention, an axial seal is provided on the shaft end which is mounted within the pump casing, a rotating part of said axial seal being led on the shaft end and a non-rotating part of the axial seal being led within the pump casing in an axially movable manner. Thereby, according to the invention, a sealing means (a sealing device) is provided between the non-rotating, axially movably mounted part and the pump casing, in order there to prevent a flow of fluid from the delivery side over to the suction side. A pump casing in the context of the present invention is also to be understood as an intermediate component which is integrated into the pump casing and on which the sealing means engage. 
         [0007]    A basic concept of the solution according to the invention, on the one hand is to provide a hydraulic force compensation which reduces the axial forces of the pump shaft acting upon the bearings, but on the other hand to provide an axial seal which only has a low friction and thus a low wearing, but which is simple in construction and reliable with regard to its effect, on the shaft end mounted within the casing. This is achieved by way of the rotating part of the axial seal being provided on the shaft end, and the non-rotating part within the pump casing. However, the non-rotating part of the axial seal is advantageously mounted and guided within the pump casing in an axially movable manner, in order be able to compensate possible wear or axial play of the shaft, wherein sealing means are provided between the axially movably mounted part of the axial seal and the pump casing. The complete sealing is thus divided into a purely axial seal as well as a further seal, preferably a radial seal, wherein the predominant movement is accommodated in the region of the axial seal, whereas the other, in particular radial seal only has to carry out small axial movements and thus, inherent of the design, is only subjected to low wear. This further, in particular radial seal can therefore be formed inexpensively, for example by way of an elastic sealing ring, whereas the axial seal can be designed exclusively for sealing with respect to the rotation movement, by way of suitably designed sealing surfaces. Thereby, given a suitable design of the axial seal, this can also accommodate axial forces and thus assume the function of a thrust bearing. 
         [0008]    According to the invention, one envisages subjecting the shaft end which is mounted within the pump casing to the pressure of the delivery side, in order in particular to largely compensate the axial forces resulting due to the hydraulic forces. However, the design according to the invention in a particularly advantageous manner envisages the sealing not being effected by a seal between a stationary and a rotating component, but between the pump casing and the axially movably mounted and non-rotating part of the axial seal. This solution has the advantage that the seal merely needs to accommodate the typically slight axial movement of the non-rotating part of the axial seal, but not the friction-intensive and wear-creating movement to the rotating part and which is accommodated by the axial seal. Inasmuch as this is concerned, the sealing is effected by the sealing gap itself, which, given suitably dimensioned axial seal, is sufficiently small so as to be able to neglect overflow losses. The sealing means can therefore be designed in an inexpensive manner and in a manner which is stable over the longer term, without this having a noticeable influence on the efficiency of the pump. 
         [0009]    The solution according to the invention also has the advantage that axial forces of the shaft can be accommodated by the axial seal in the pump casing, at least to a limited measure. The significant part of the axial forces however is produced by the hydraulic compensation, which means the leading of the pressure level produced by the pump, back onto the free shaft end within the pump casing, so that the drive of the pump can be ensured by a standardized motor, irrespectively of the stage number. The dynamic force compensation of the hydraulically caused axial forces acting upon the shaft limits the forces to be accommodated by the thrust bearing to a minimum. The hydraulic force compensation also has the advantage that a force compensation is also not effected in the case of a dry running, when these restoring forces do not occur, so that even then the wearing is kept to within acceptable limits. 
         [0010]    The design according to the invention moreover has the advantage that with a suitable design implementation, the axial seal as well as the remaining sealing means, in particularly the radial seal, can be exchanged without having to remove the shaft out of the pump casing. Pump stages, which is to say the impellers with the associated diffusers can therefore also remain in their designated position. 
         [0011]    It is particularly advantageous if the non-rotating part of the axial seal is subjected to the pressure of the delivery side of the pump, at the axial side of this non-rotating part which is away from the sealing surface, thus rear side. The necessary support force for the axial seal or for the thrust bearing function is mustered by way of this, and specifically in a dynamic manner, which is to say in dependence on the exit pressure of the pump. 
         [0012]    This can advantageously be developed further by way of the non-rotating part of the axial seal comprising a ring, whose one axial face side forms a sealing surface of the axial seal and whose other axial side which is away from this, thus the rear-side axial side is configured in a closed manner and comprises at least one recess, whose pressure-effective cross-sectional area is smaller than the pressure-effective cross-sectional area of the conduit connection to the delivery side. Thereby, a recess in the context of the present invention can be an edge gap, an opening, one or more through-holes or a combination thereof. What is essential is the fact that the pressure-effective cross-sectional area of the one or more recesses is always smaller than the pressure-effective cross-sectional area of the one or the several conduit connections to the delivery side, in order to ensure that a pressure firstly forms in front of this closed surface of the ring on starting operation of the pump, and this pressure leads to the ring moving axially in the direction of the counter-sealing surface at the shaft end, and this additional axial force creating the movement of the ring only decreasing when the interior delimited by the ring is completely filled with fluid after a certain time. 
         [0013]    An O-ring which is held in a radially peripheral groove is advantageously provided for sealing the axially movable part of the axial seal and the pump casing or the component which is provided within the pump casing for receiving the axially movable part. This radially peripheral groove can either be provided on the casing side or ring side, thus bearing side. Such an O-ring is inexpensive, simple to assemble and exchange as the case may be, and forms a reliable seal over the longer term. 
         [0014]    It is particularly advantageous if the O-ring lies in a peripheral groove which is provided on the inner side of a holding ring and which is fixed in the pump casing. Such a design, with which the O-ring is not led directly in the pump casing, but in an intermediate component, has the advantage that here only the holding ring needs to be machined in a material-removing manner, and the holding ring for example is integrated by way of pressing into the pump casing, and no chucking of the pump casing on manufacture of the groove is necessary inasmuch as this is concerned. 
         [0015]    The non-rotating part of the axial seal can be formed from a solid material, for example as a turned part, in order to form the closed axial side of this part. However, it is particularly advantageous if this part is formed as a ring from a tube section, and the closed axial side can be created by a sheet-metal section which can be inexpensively manufactured by way of punching. This sheet-metal section which covers the ring at the rear side and thus forms the initially pressure-effective closed axial side with the at least one recess, can moreover be advantageously utilized, in order to form the rotation lock of the non-rotating part of the axial seal, in particular of the ring and to fix this in a rotationally fixed manner either on the holding ring and/or on the pump casing. Since only small forces are to be accommodated inasmuch as this is concerned, this function can also be realized by way of an inexpensive punched part which as the case may be is likewise machined in a shaping manner. 
         [0016]    According to the invention, one envisages connecting a holding ring in a sealed and fixed manner to the shaft end, at the shaft side, wherein this holding ring is either itself configured as a sealing ring and forms an axial sealing surface or advantageously receives a rotating ring forming the axial sealing surface. Such a rotating ring for example can consist of a highly wear-resistant silicon carbide, wherein the holding ring can consist of a less expensive, preferably metallic material. Thereby, the rotating ring forming the axial sealing surface can advantageously be fixed on the holding ring or with this holding ring by way of a threaded sleeve which is screwed into the holding ring, or by a sleeve. This permits the exchange of the rotating ring forming the axial sealing surface, likewise without a disassembly of the shaft, since the free end of the shaft is accessible from outside the pump casing and can be blocked from rotating by way of a tool. 
         [0017]    The centrifugal pump according to the invention is advantageously configured as an inline pump, thus comprises a pump casing with which the suction connection and delivery connection are arranged on the same axis. A channel between the delivery connection and a space which receives the non-rotating part of the axial seal and is typically arranged in the foot of the pump casing can be realized in a simple manner with such an arrangement. Several channels can also be provided as the case may be, in order to realize the required conduit cross sections. 
         [0018]    One of the sealing surfaces of the axial seal is advantageously configured as a three-point contact, thus comprises three macroscopic prominences which are distributed over the periphery, and which one the one hand ensure a defined contact to the plane counter-sealing surface and on the other hand are particularly advantageous with regard to the build-up of a lubricant film, wherein this lubricant film should be built up as rapidly as possible on starting up the pump, so that the advantageous and low-wear sliding friction arises. The design of this three-point contact is effected advantageously on the rotating ring, since this as a separate component can be machined less expensively with a lower tolerance than the remaining components. 
         [0019]    The design according to the invention permits the axial mounting of the shaft to be provided exclusively at the motor side, wherein the axial forces which thereby occur are so small inherently of the design, that they can be accommodated by the motor bearings, without noticeably increasing their wear. The axial mounting of the shaft is therefore advantageously effected by way of one or more bearings which are arranged on the motor side, preferably a motor-side bearing close to the pump-side end of the motor shaft. 
         [0020]    According to an advantageous further development of the invention, the ring of the non-rotating part of the axial seal can alternatively or additionally be constructed in a multi-part manner and comprise a highly wear-resistant part having the sealing surface, as well as a carrier receiving the highly wear-resistant part, as has already been specified above for the rotating part of the axial seal. 
         [0021]    The rotating ring and/or the highly wear-resistant part of the ring can advantageously be formed of silicon carbide or a comparably highly wear-resistant material, which permits particularly long service lives. 
         [0022]    According to an advantageous further development of the invention, a closable opening can be provided in the pump casing, preferably aligned to the axial seal, through which opening the axial seal can be exchanged, in order to be able to exchange the axial seal and the sealing means between the non-rotating part of the axial seal and the pump casing, without having to disassemble the pump. 
         [0023]    The invention is hereinafter explained in more detail by way of embodiment examples represented in the drawing. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    In the drawings: 
           [0025]      FIG. 1  is a greatly simplified schematic, longitudinal, sectional view through a multi-stage centrifugal pump of the inline construction type with a drive motor; 
           [0026]      FIG. 2  is an enlarged longitudinal, sectional view of the pump which is rotated by 90° with respect to  FIG. 1 ; 
           [0027]      FIG. 3  is an enlarged view of the detail III in  FIG. 1 ; 
           [0028]      FIG. 4  is an enlarged view of the detail IV in  FIG. 2 ; 
           [0029]      FIG. 5  is a longitudinal, sectional view showing the rotating part of the axial seal; 
           [0030]      FIG. 6  is an exploded view of the components of the rotating part of the axial seal; 
           [0031]      FIG. 7  is an exploded view of the non-rotating part of the axial seal with a holding ring for integration into the pump casing; 
           [0032]      FIG. 8  is an exploded view of the components of the non-rotating part of the axial seal; 
           [0033]      FIG. 9  is an exploded view of the axial seal and the foot part of the centrifugal pump; and 
           [0034]      FIG. 10  is an enlarged view of the centrifugal pump from below. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]    With the centrifugal pump which is represented by way of  FIGS. 1-10  it is the case of a multi-stage centrifugal pump  1  of the inline construction type which is operated in a standing manner. The pump casing comprises a foot part  2 , a head part  3  and a cylindrical jacket  4  which is arranged therebetween and which surrounds the pump stages and is clamped between the head part  3  and the foot part  2 . The foot part  2  comprises a suction connection  5  as well as, aligned to this, a delivery connection  6 . The head part  3  is designed as a motor stool and surrounds a coupling  7  which connects a shaft  51  of an electric motor  50  schematically represented in  FIG. 1  and attached on the head part  3 , to a shaft  8  of the pump  1  in a rotationally fixed manner. The shaft  8  of the pump  1  carries the impellers  9  of the pump stages and is rotatably arranged within the pump casing. A radial seal  10  is provided in the head part  3 , and an axial seal  11  is provided in the foot part  2 . The construction of this axial seal  11  is evident in detail from the  FIGS. 3 to 8  and is described in a detailed manner further below. Fluid is brought into the pump casing on operation via the suction connection  5 , when the shaft  8  rotates, and this fluid enters into the suction port  12  of the first pump stage and is delivered through the pump stages which are formed in each case by an impeller  9  and a surrounding diffuser  13 , until it exits from the last pump stage in the head part  3  and is led back via an annular channel  14  to the delivery connection  6 , through which the fluid leaves the pump again. 
         [0036]    The casing-side shaft end  15  of the pump in the region of the suction port  12  lies below the first pump stage. It comprises a pocket-hole bore  16  which is provided with a thread and in which a cap screw  17  is seated, with which cap screw a holding ring  18  is sealingly and fixedly fastened on the shaft end  15 . The holding ring  18  comprises a wall  19  which is directed to the suction port  12  and is closed with the exception of a central recess for leading through the screw  17 , thus is configured in a pot-like manner and is fixedly connected to the shaft end  15  in a sealed manner. 
         [0037]    The holding ring  18  is configured as a turned part, is stepped to the side which is away from the shaft end  15  and is formed with a peripheral groove which is open to the bottom and which is provided for receiving a rotating ring  20 . The rotating ring  20  consist of silicon carbide and is rotationally secured in the holding ring  18  by way of pins  21  and is otherwise fastened together with the holding ring  18  on the shaft end  15 , by way of a sleeve  22  which radially encompasses the rotating ring  20  on the inner side and by way of the screw  7 . The rotating ring  20  comprises a downwardly directed axial surface  23  thus which is directed away from the shaft end  15  and this surface forms the rotating axial surface of the axial seal  11 . This axial surface  23  is not completely planar, but comprises three macroscopic prominences which are uniformly distributed over the periphery and which on the one hand form a defined contact on the counter-surface  24 , which is to say on the axial surface  24  of the non-rotating axial seal part  25 , and on the other hand serve for the rapid build-up of the lubricative film. The axial surface  24  is configured in a planar manner and is part of the non-rotating part, here of the ring  25  which is arranged in an axially movable manner within a holding ring  26  integrated in a corresponding receiver in the lower side of the foot part  2  of the pump casing. 
         [0038]    The holding ring  26  comprises a peripheral groove  27  on its inner side, in which groove an O-ring  28  is integrated, said O-ring radially sealing the ring  25  with respect to the holding ring  26  and thus with respect to the pump casing. The holding ring  26  is moreover yet sealed with respect to the receiver in the pump casing by way of an outer-peripheral seal  58 , as is evident from the sectioned representations  4  and  7 . 
         [0039]    The non-rotating ring  25  at the rear side which is away from the axial sealing surface  24  is covered by a sheet metal section  20  which almost completely covers this rear side of the sealing ring  25 . The sheet-metal section  20  comprises bent-over tongues  30 , with which the sheet metal section is integrated within corresponding recesses  52  on the rear side of the ring  25  with a positive fit. These tongues  30  project radially beyond the ring  25  and engage into these recesses  52  in the ring  25  and form part of a rotation lock of the non-rotating ring  25 . Moreover, the sheet-metal section  29  comprises two diametrically opposite tongues  31  which are offset by 90° to the tongues  30  and which are bent away upwards out of the plane of the main material by 90° and connect the sheet-metal section  29  in an axially distanced manner to the ring  25 , in which the ends  53  engage into a shoulder  54  on the inner side of the ring  25  in a locking manner. 
         [0040]    The sheet-metal section  29  forms a closed surface of the lower side of the ring  25  and comprises a central rectangular recess  32 , into which a pin  55  which is rectangular in cross section engages, said pin forming part of the holding ring  26 , on which the ring  25  comprising the axial sealing surface  24  is guided in a rotationally fixed, but axially movable manner. The pin  55  and the recess  32  with regard to cross section are dimensioned such that this recess  32  with the pin  55  located therein, together with any gap tolerances of the sheet-metal section  29  form a through-gap with a cross-sectional area which is significantly smaller than the cross-sectional area of channels  33  which are provided in the foot part  2  of the pump casing or in the holding ring  26  and which ensure that the interior  34  of the ring  25  with the sheet-metal section  29  and the holding ring  26  is subjected to the pressure of the delivery side of the pump, thus to the pressure at the delivery connection  6 . These channels  33 , on starting up the pump after an effected pressure build-up ensure that the sheet-metal section  29  with the ring  25  bearing thereon is firstly subjected to force and is pushed, in the direction of the free shaft end, thus towards the motor, since firstly fluid must flow via the smaller cross section of the gap between the recess  32  and the pin  55 , into the space enclosed by the ring, before a corresponding counter-pressure is built up. The ring  25  is moved axial upwards in  FIG. 1 , which is to say is moved axially within the holding ring  26  by way of this, until the axial surface  24  bears on the counter-surface  23 , by which means a separation between the suction-side space in the region of the shaft end  15  and the installation space  34  of the stationary part of the axial seal  11  is then also formed. The pressure of the delivery side also prevails within the ring  25  and this at the face side of the shaft  8 , as soon as the space which is enclosed by the ring  25  and the sheet-metal section  29  has filled via the gap of the recess  32 , by which means the certain force compensation with regard to the hydraulically caused axial force of the shaft  8  and which is desired on operation is effected. 
         [0041]    As can particularly be deduced from  FIG. 9 , the holding ring  26  is part of a circular disc  56  which is provided for integration in a base-side maintenance opening  60  of the pump casing, here of the foot part  2 . The disc  56 , in a manner closing this base-side opening  60 , lies in a shoulder  64  on the lower side of the foot part  2  and is releasably connected to the foot part  2  via four screws  57  which are led through recesses  61  in the edge  62  of the disc  56 . An O-ring  58  which is integrated in a peripheral radial groove of the ring  26  and serves for sealing this component with respect to a recess  63  in the foot part  2 , is arranged in the upper region of the ring  26 , thus at a small distance to the disc  25 , for sealing with respect to the foot part  2 . A second O-ring  59  is integrated at an axial distance to this, in a peripheral, radial groove in the lower part of the ring  26  and serves for sealing with respect to the maintenance opening  60  in the foot part  2 . A connection to the delivery side of the centrifugal pump  1  which is connected in a fluid-leading manner to the interior of the ring  26  via channels  33  in the ring  26 , connects within the foot part  2 , between the O-rings  58  and  59 , so that the pressure of the delivery side via this connection is present at the surface of the non-rotating part  25  of the axial seal, said surface being formed by the sheet-metal section  29  and at the beginning being pressure-effective. The ring  26  via the O-ring  28  lying in a groove on the inner side of the holding ring  26  is sealed with respect to the ring  25  which forms the non-rotating part of the axial seal with the axial surface  24  of the seal. This O-ring  28  thus forms a radial seal which however only has to accommodate the comparatively small movements in the axial direction and therefore is only subjected to a low wear. 
         [0042]    The axial seal can be overhauled and exchanged as the case may be, by way of removing the disc  56  with the holding ring  26  which is located thereon, after the screws  57  have been released, due to the fact that the pump casing at the lower side, thus in the base of the foot part  2 , comprises a maintenance opening  60  which is closed by the disc  56 . The shaft  38  of the pump does not have to be removed for this. All components of the axial seal which are represented in the exploded representation according to  FIG. 9  can be exchanged through the opening  61  in the base of the foot part  2 . An exchange of the components comprising the axial surfaces  23  and  24  as well as of the O-ring  28  is effected in the simplest case. The shaft  8  in the region of the motor stool has a cross-sectional profile which permits a locking of the shaft by way of laterally engaging a tool, in order to be able to release the threaded connections which are connected to the shaft  8 . Thus, the cap screw  17  can be released after the shaft  8  is held in a rotationally fixed manner by way of a spanner introduced in the region of the motor stool, and this screw can then be tightly screwed again after exchange of the rotating ring  20  and, as the case may be, further seals of the holding ring  18 . 
         [0043]    The axially stationary part of the seal, thus the non-rotating ring  25  with its seals and the holding ring  26  which with the disc  56  forms the cover for closure of the casing opening of the maintenance opening  60 , together with the cover  56  are pulled out downwards and thereby the upper part of the holding ring  26  with the peripheral O-ring  58  is pulled out of the recess  63 , and the lower part of the holding ring  26  with the O-ring  59  is pulled out of the maintenance opening  60 . These seals as well as the O-ring  28  and the non-rotating part of the axial seal  25  can then be exchanged and together are inserted from below into the maintenance opening  60  or the recess  63  of the foot part  2 , until the upper part of the holding ring  26  with the O-ring  58  sealingly bears in the recess  63  and the lower part with the O-ring  59  sealingly bears in the maintenance opening  60 . 
         [0044]    While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles. 
       APPENDIX 
     List of Reference Numerals 
       [0000]    
       
           1 —centrifugal pump 
           2 —foot part 
           3 —head part 
           4 —jacket 
           5 —suction connection 
           6 —delivery connection 
           7 —coupling 
           8 —shaft 
           9 —impellers 
           10 —radial seal 
           11 —axial seal 
           12 —suction port 
           13 —diffuser 
           14 —annular channel 
           15 —shaft end 
           16 —pocket-hole bore 
           17 —cap screw 
           18 —holding ring 
           19 —wall 
           20 —rotating ring 
           21 —pins 
           22 —sleeve 
           23 —axial surface 
           24 —axial surface 
           25 —non-rotating part of the axial seal, ring 
           26 —holding ring 
           27 —groove 
           28 —O-ring 
           29 —sheet-metal section 
           30 —tongues 
           31 —tongues 
           32 —recesses in  29   
           33 —channels in ring  26   
           34 —interior of  25   
           35 —outer thread 
           36 —nut 
           37 —sleeve 
           37 —shaft 
           50 —motor 
           51 —motor shaft 
           52 —recesses in ring  25   
           53 —ends of the tongues  31   
           54 —shoulder in ring  25   
           55 —pin 
           56 —disc/cover 
           57 —screws 
           58 —O-ring 
           59 —O-ring 
           60 —maintenance opening 
           61 —bores for the screws  57   
           62 —edge of cover 
           62 —recess 
           64 —shoulder in foot