Abstract:
A multi-stage centrifugal pump includes a pump casing, in which a shaft ( 8 ) carrying an impeller is rotatably arranged. The pump casing has a pump casing foot part ( 2 ) that includes a reversibly closable maintenance opening ( 60 ), via which a bearing and/or seal ( 20, 25 ), which is arranged at a shaft end within the pump casing, is accessible and exchangeable.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119 of European Application 15 195 415.3 filed Nov. 19, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to a multistage centrifugal pump with a pump casing and with a shaft which carries the impellers of the pump stages and which is rotatably arranged within the pump casing. 
       BACKGROUND OF THE INVENTION 
       [0003]    Centrifugal pumps of this type and in numerous variants are counted as belonging to the state of the art. In this context, Grundfos pumps (of the Applicant) of the CR series, or Lowara X pumps (of the Xylem concern) of the SV-series are referred to. Such multi-stage centrifugal pumps comprise a common shaft, which carries impellers of pump stages and which is rotatably arranged within a pump casing. Thereby, the drive, in particular with pumps of a larger construction type, is mostly effected via an external motor which is drive-connected to the pump shaft via a coupling. Such pumps are often envisaged for operation with a vertical shaft, and the pump casing therefore comprises a foot part forming the placement surface of the centrifugal pump, as well as a head part designed as a motor stool or comprising such, on which the drive motor is fastened. The pump stages are integrated between the head part and the foot part which are often at least partly manufactured from cast metal, and these pump stages are closed off by a peripheral jacket and are connected to one another via tie rods amid the inclusion of the pump stages. If the centrifugal pump is designed as an inline pump, then on the foot part side it comprises a suction connection and a delivery connection which are offset by 180° to one another. The fluid entering into the pump via the suction connection and running through the individual pump stages is led upwards in each case amid the increase of pressure, where in the head part it is led again to the foot part via an annular channel formed between diffusers and the outer casing, and there to the delivery connection. The shaft carrying the impellers is led out at the motor-side end in a sealed manner. It is counted as belonging to the state of the art, to apply a sealing cartridge in this region, in order to be able to exchange the seal in a quick and simple manner in the case of wear. A bearing can be provided at the other end of the shaft, thus the end which is located within the pump casing. It is also counted as belonging to the state of the art to subject this shaft end to the pressure of the delivery side, in order to hydraulically compensate the axial forces acting upon the shaft. It is then regularly necessary to provide a seal in this region. 
         [0004]    It always requires a certain amount of effort to exchange a seal, a bearing or both in the case of a defect or wear, irrespective of whether these are present individually or both are present. The pump is to be dismantled in large parts for this. The tie rods and further components are to be removed, in order to be able to exchange the bearing and/or the seal at the casing-side end, thus in the region of the foot part. This work is time-consuming and is thus expensive. 
       SUMMARY OF THE INVENTION 
       [0005]    Against this background, it is an object of the invention, to design a generic multistage centrifugal pump such that the previously mentioned repair and maintenance work is simplified, without the manufacturing costs of the pump being significantly increased by way of this. 
         [0006]    The multi-stage centrifugal pump according to the invention comprises a pump casing, in which a shaft is rotatably mounted, said shaft carrying impellers of the pump stages. The pump casing comprises a reversibly closable maintenance opening, via which a shaft end cooperating part, a bearing which is arranged within the pump casing at the shaft end and/or a seal which is arranged within the pump casing at the shaft end, is accessible and exchangeable. 
         [0007]    A basic concept of the solution according to the invention, it to provide a maintenance opening within the pump casing, typically at the base side, said opening only being opened for maintenance purposes and being sealingly closed on remaining operation, but permitting the control, the maintenance or, as the case may be, the exchange of wear-sensitive components on the shaft end (wear-sensitive shaft end cooperating parts) located within the pump casing, be they a bearing and/or seal, in a targeted manner, without having to dismantle the complete pump, in particular without having to release the tie rods, for this. Such an additional maintenance opening as a rule can be provided with little expense with regard to manufacturing technology, and one merely needs only to provide a component closing this opening, as the case may be amid the integration of a seal, which with regard to the design is mostly possible without any problem. The maintenance opening, as the case may be, can be opened and closed again several times, due to the fact that the maintenance opening is reversibly closable. 
         [0008]    The maintenance opening, in particular if it is arranged on the foot part which is mostly designed as a cast component, can be formed by a simple recess in the base. Such an opening in the simplest form can be closed by a screw-fastened cover. Thereby, it can either be the case of a cover which encompasses (overlaps) the opening and which is fastened by way of fastening screws engaging into the respective casing component laterally of the opening, or however it can be the case of a cover which comprises a thread on its outer periphery, said thread engaging into an inner thread of the opening. The first variant is advantageous with regard to the cost and is simple to seal, by way of a flat seal being integrated between the components or by providing an O-ring with the provision of a cover seal-side or casing-side groove. 
         [0009]    Means for blocking the rotation movement of the shaft are advantageously to be provided, in order to be able to exchange the bearing parts or seal parts which are fastened on the shaft end, for example by way of a screw connection. These means do not necessarily have to be provided on this shaft end, but for example can also be provided on the head of the pump outside the casing, if for example the shaft there has a square or hexagonal profile, onto which a spanner can be placed. A suitable profile for the engagement of a tool can alternatively also be provided at the free shaft end within the casing or, or a transverse bore in the shaft end, through which a blocking pin can be placed. 
         [0010]    It is advantageous to arrange the maintenance opening in the base of the pump casing, if the centrifugal pump is designed for operation with a vertically arranged shaft. However, multi-stage centrifugal pumps which are designed for operation with a horizontally arranged shaft are also known. With these pumps too, it is advantageous to incorporate the maintenance opening in a casing wall in a manner aligned to the shaft, and specifically at the side of the casing which is away from the motor, thus on a wall of the casing which is remote from the motor. 
         [0011]    Basically, it is useful to place the maintenance opening such that the bearing and/or the seal at the shaft end is/are easily accessible. This can be effected by a lateral opening in the casing. However, it is particularly useful for the opening to be aligned to the shaft. Aligned to the shaft is not to be understood in the strict geometric sense, but the opening can also be aligned to the shaft, thus to the shaft axis, in a slightly offset manner, depending on which is more favorable with regard to the design. 
         [0012]    It is particularly advantageous if the cover not only has a purely closing function, but simultaneously fulfils further functions. Thus according to a further development of the invention, the cover can comprise a part which passes through the opening and which receives or forms a rotationally fixed part of the seal or of the bearing. Such an arrangement has the advantage that on removal of the cover, not only is an access to the seal or the bearing at the free shaft end created, but at the same time a part of the seal or of the bearing is formed or is held. Then specifically, a part of the bearing or of the seal is also disassembled already after the disassembly of the cover, which on the one hand simplifies the examining of the condition and on the other hand also simplifies the exchange in the case of a repair. It is then advantageous if the other part of the seal or of the bearing is releasably fastened on the shaft end which is arranged within the pump casing. Thereby, the co-rotating part for example can be fastened by way of a screw engaging into a threaded bore of the shaft end or be placed onto the shaft end and be fixed there by way of a nut. 
         [0013]    It is usually necessary to block the shaft, in order to prevent a co-rotation, for the release of such a screw connection. This in the simple case can be envisaged by a profile which is incorporated on the led-out shaft end, or a transverse bore through the shaft. Basically, it is also conceivable for blocking means to be provided on the motor shaft. 
         [0014]    If the cover according to a further development of the invention is designed such that it overlaps the maintenance opening and is screw-fastened on the pump casing in the overlapping part, then this can be sealed in a simple manner, e.g. by way of a flat seal. The assembly and disassembly is configured in a simple manner, since the screws as a rule are easily accessible given a suitable alignment of the pump. Such an arrangement is then advantageous, in particular if the cover assumes further functions such as for example carrying the stationary part of the bearing or of the seal, since one can ensure adequately large contact surfaces, in order to ensure the required exact alignment of the components to one another. Moreover, the machining of the casing around the cover opening as well as the formation of threaded bores or stud bolts which are provided there can be manufactured in the same chucking on the machine tool. The cover itself can be formed of sheet metal or of cast metal. 
         [0015]    It is particularly advantageous to arrange the maintenance opening within the foot part, preferably on the base side, if the centrifugal pump is designed as an inline pump, whose suction and delivery connections are arranged on the foot part side. Thereby, the centrifugal pump advantageously comprises an axial seal at the shaft end, the stationary part of said axial seal comprising a ring which is arranged in an axially movable manner within the pump casing or within a component integrated therein. Such a design, with which on the one hand a hydraulic pressure impingement of the free shaft end is formed for the compensation of the axial forces acting on the pump shaft and on the other hand a low-friction, but effective axial seal which is less prone to wear is formed, is particularly advantageous. This axial seal can be controlled, overhauled and exchanged in a rapid and simple manner by way of the maintenance opening. Thereby, the stationary part of the axial seal which is axially movably mounted within the pump casing is mounted in the cover, with which the maintenance opening is closed. 
         [0016]    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 
         [0017]    In the drawings: 
           [0018]      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; 
           [0019]      FIG. 2  is an enlarged, longitudinal, sectional view of the pump which is rotated by 90° with respect to  FIG. 1 ; 
           [0020]      FIG. 3  is an enlarged representation showing the detail III in  FIG. 1 ; 
           [0021]      FIG. 4  is an enlarged representation showing the detail IV in  FIG. 2 ; 
           [0022]      FIG. 5  is a longitudinal, sectional view showing the rotating part of the axial seal; 
           [0023]      FIG. 6  is an exploded representation showing the components of the rotating part of the axial seal; 
           [0024]      FIG. 7  is a longitudinal, sectional view showing the non-rotating part of the axial seal with a holding ring for integration into the pump casing; 
           [0025]      FIG. 8  is an exploded representation showing the components of the non-rotating part of the axial seal; 
           [0026]      FIG. 9  is an exploded representation showing the axial seal and the foot part of the centrifugal pump; and 
           [0027]      FIG. 10  is an enlarged view of the centrifugal pump from below. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    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. 
         [0029]    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 designed in a pot-like manner and is fixedly connected to the shaft end  15  in a sealed manner. 
         [0030]    The holding ring  18  is designed 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 designed 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. 
         [0031]    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 . 
         [0032]    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  29  which almost completely covers this rear side of the sealing ring  25 . The sheet-metal section  29  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. 
         [0033]    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. 
         [0034]    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. 
         [0035]    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 . 
         [0036]    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 . 
         [0037]    The exchange of the axial seal at the lower shaft end is described above, however it is to be understood that according to the invention, a bearing which is provided between the shaft and the casing can also be exchanged in an analogous manner, without the shaft having to change its position within the pump casing and thus extensive disassembly and assembly activities becoming necessary. 
         [0038]    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 
           38 —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 
           63 —recess 
           64 —shoulder in foot