Patent Publication Number: US-11396890-B2

Title: Magnetically coupled sealless centrifugal pump

Description:
RELATED APPLICATIONS 
     This is a Continuation Application of U.S. application Ser. No. 15/799,572, filed Oct. 31, 2017, which claims priority to U.S. Provisional Application 62/416,059, filed Nov. 1, 2016, the disclosures of which is incorporated herein by reference in their entirely. 
    
    
     BACKGROUND OF THE INVENTION 
     The field of the present invention is pumps which are magnetically engaged. 
     Pumps that utilize an open/semi-open impeller need a means to adjust the impeller axially relative to the pump case. As the impeller and case wear over time, the clearance between the impeller and the case opens up. This degrades performance; the pump efficiency decreases; and the produced pump pressure can decrease. The impeller is then set to the appropriate clearance from the case during each maintenance cycle, using the external provisions of the pump, thereby not requiring the pump to be taken out of service. The concept of having a rotor that is externally adjustable is industry standard for normal sealed pumps. The mechanisms accompanying axial adjustment in a sealed pump are generally located in the power frame. This is possible with a sealed pump because the impeller is mechanically connected to the ball bearings (in the power frame) through the shaft, etc. 
     Other features are commonly employed. Shunted process fluid is frequently used for lubrication of bearing surfaces. In magnetically coupled sealless pumps, the bearing surfaces and the interior magnets of the magnetic coupling conventionally are wetted, while the exterior magnets are in atmosphere. Such arrangements require bearing and magnetic mountings on multiple elements. 
     Rub rings are commonly employed with a component to restrict eccentric rotation upon catastrophic bearing failure. Such rotation can damage sealing canisters. Plates are also used to protect workers from catastrophic component failure. Often, component complexity in arranging these and other details is dictated in magnetically coupled pumps by the pump drive being concentrically outwardly of the driven rotor assembly, usually including an impeller shaft. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a magnetically driven centrifugal pump including a pump case, an impeller, a stuffing box and magnetic coupling between an impeller rotor and a drive. A canister extends through the magnetic coupling to form a barrier between the impeller rotor side and the drive side of a pump. 
     The stuffing box includes a stuffing box outer fixed to the pump case and a stuffing box inner threadedly engaged with the stuffing box outer about the axis of impeller rotation. The impeller rotor is axially fixed relative to the stuffing box inner. Rotation of the stuffing box inner relative to the stuffing box outer can then adjust the impeller clearance in the pump case. 
     An annular rotor bushing may be between the rotor and the stuffing box inner; an annular impeller bushing may be between the impeller hub and the stuffing box inner and two opposed thrust bushings are between the stuffing box inner and the rotor. All may be mounted exterior to the drive. This common access simplifies the stuffing box and facilitates ease of service. 
     Accordingly, it is an object of the present invention to provide an improved magnetically coupled centrifugal pump. Other and further objects and advantages will appear hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional elevation of a magnetically driven centrifugal pump taken through the axis of impeller rotation; 
         FIG. 2  is a cross-sectional detail of the stuffing box illustrated in  FIG. 1 ; 
         FIG. 4  is a cross-sectional elevation of a second embodiment of a magnetically driven centrifugal pump taken through the axis of impeller rotation; 
         FIG. 5  is a cross-sectional detail of the stuffing box illustrated in  FIG. 4 ; and 
         FIG. 6  is a detail of the magnets and bushings in the stuffing box of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning in detail to the drawings, the Figures each show the surface of sections through the access of impeller rotation  10 . The major components except for the pump case and the pump housing, which are asymmetrical because of volutes and mountings, respectively, are substantially symmetrical about the axis of impeller rotation. The first embodiment,  FIGS. 1 through 3 , differ from the second embodiment,  FIGS. 4 through 6 , by the support arrangements for the impeller. In both embodiments, a bushing is about the hub of the impeller to securely support the rotatable impeller. 
     A pump case  12  defining an impeller cavity and a volute is further defined by a housing structure  13 . The pump case  12  surrounds an open vane impeller  14  while the housing structure  13  extends over a stuffing box  16 . The impeller  14  includes an impeller hub  15  extending away from the vanes of the impeller  14 . The pump case  12  and housing structure  13  are conventionally assembled with bolts. The housing structure  13  is shown in this instance to have an open arrangement with holes about the circumference. 
     The stuffing box  16  includes a stuffing box outer  18  which is a collar with an outer flange  19  engaging the pump case  12  and held in place by the housing structure  13 . The stuffing box  16  further includes a stuffing box inner  20  engaged with the stuffing box outer  18  at a threaded engagement  22 . The threaded engagement  22  provides for the stuffing box inner  20  to be rotated relative to the stuffing box outer  18  to allow axial translation of the stuffing box inner  20  relative to the stuffing box outer  18  and in turn the pump case  12 . After the desired axial position of the stuffing box inner  20  is achieved, the rotational position of the stuffing box inner can either be held by thread friction or by an external set screw. The stuffing box inner  20  extends from the threaded engagement  22  as a cylinder to a stuffing box inner detachable cap  24 . The stuffing box inner detachable cap  24  is held in place by fasteners. 
     A rotor  26  is located within the annular cavity defined within the stuffing box inner  20 . The rotor  26  is also cylindrical with a front wall. A mounting hub  27  fixed on the cylindrical front wall threadedly engages the impeller hub  15  so that the impeller  14  is detachably fixed to the rotor  26 . With the rotor  26  located in the annular cavity with thrust bushings described below, the rotor  26  moves axially with the stuffing box inner  20  relative to the stuffing box outer  18 . With the stuffing box outer  18  engaging the pump case  12  and the rotor  26  being engaged through the mounting hub  27  with the impeller hub  15 , the axial adjustment of the stuffing box inner  20  relative to the stuffing box outer  18  is used to create an appropriate clearance between the impeller  14  and the pump case  12 . 
     A drive  28  is arranged inwardly of the rotor  26 . The drive  28  includes a drive output  29  that is cylindrical with an engagement to receive a drive shaft coupled with a motor (not shown) for torque transfer. The drive further includes a drive shaft power frame  30  with a shaft conventionally arranged in with bearings as shown to transfer rotary power from the motor. The housing is conventionally coupled with the housing structure  13  by bolts. 
     Power to the rotor  26  from the drive  28  is transmitted through a magnetic coupling  31 . The magnetic coupling  31  is traditional including driving magnets  32  associated with the drive  28  and driven magnets  34  associated with the rotor  26 . A canister  36  extends through the magnetic coupling. The canister  36  is integrally formed with the stuffing box inner detachable cap  24 . The stuffing box inner detachable cap  24  and the associated canister  36  are retained by fasteners at the end of the stuffing box inner  20 . Thus, the canister  36  does not rotate with either the rotor  26  or the drive  28  but remains stationary in the pump unless the impeller  14  is being axially adjusted. The canister  36  includes a concave end which results in less distortion of the canister  36  under pressure loads from the pump process fluids. 
     In the preferred embodiment, the rotating components within the stuffing box  16  are mounted through bushings. The bushings used in these embodiments are bushing pairs each with a static bushing associated with the stuffing box inner  20  and a dynamic bushing each associated with the rotor/impeller assembly  26 / 14 . These components are held in place by conventional means. An annular rotor bushing  38  is located between the stuffing box inner  20  and the rotor  26 . The annular impeller bushing  40  is between the stuffing box inner  20  and the impeller hub  15 . In the first embodiment as illustrated in  FIGS. 1 through 3 , the mounting hub  27  includes an outer ring  41 . The annular impeller bushing  40  is engaged with the mounting hub  27 . This arrangement thus allows engagement of all of the bushings with the rotor  26 . At the same time, the annular impeller bushing  40  remains between the stuffing box inner  20  and the impeller hub  15  to positively mount the impeller  14 . In the second embodiment, as seen in  FIGS. 4 through 6 , the bushing  48  directly engages the impeller hub  15  to the same end. With either arrangement, the rotor  26  is rotationally mounted by the annular rotor bushing  38  and the annular impeller bushing  40  within the stuffing box inner  20 . 
     A forward thrust bushing  42  is arranged between the stuffing box inner detachable cap  24  and the rotor  26 . A rearward thrust bushing  44  is located between the stuffing box wall  25  and the rotor  26 . The thrust bushings  42 ,  44  thus retain the rotor  26  fixed axially within the stuffing box inner  20 . Again, all of the annular and thrust bushings are traditionally placed within the pump. 
     A process fluid shunt  46  lubricates the bushings located about the rotor. A shunt inlet  48  is located outwardly of the impeller hub  15  to extend through the annular impeller bushing  40 . A gap between the rotor  26  and the stuffing box wall  25  directs process fluid through the rearward thrust bushing  44 . An annular gap between the stuffing box inner  20  and the rotor  26  then permits the shunted process fluid to move to and through the annular rotor bushing  38 . An annular cavity adjacent the annular rotor bushing  38  defined in the stuffing box inner detachable cap  24  then directs the shunted process fluid through the forward thrust bushing  42 . The shunted process fluid is then released to around the canister  36  where it passes by the wetted magnets  34  and then to the shunt return  50  along the access of impeller rotation  10 . The shunt inlet  48  is located outwardly on the open vane impeller  14  of the shunt return  50  located along the access of impeller rotation  10 . Thus, rotation of the impeller  14  is able to drive circulation of the shunted process fluid. 
     A rub ring  52  closes the drive end of the stuffing box inner  20  by extending inwardly to the drive  28 . In addition to closing the stuffing box inner  20 , the rub ring  52  is associated with a circumferential ring  54  located on the drive  28 . The maximum compressive deformation in the ring  54  is less than the gap between the canister  36  and either of the magnet assemblies  32 ,  34 . This prevents damage to the canister  36  by catastrophic failure of any of the bearings. 
     Thus, an improved magnetically coupled centrifugal pump is shown and described. While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art that many more modifications are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims.