Patent Abstract:
Axial adjustment apparatus is provided in a centrifugal pump to effect adjustment of the impeller relative to adjacent pump elements. Specifically preferred is adjustment apparatus in a chopper pump that provides adjustment of the impeller relative to a chopper plate to facilitate continuous efficient cutting of solids by the pump. The adjustment apparatus may also include adjustment structure for providing axial adjustment between the impeller and a plate-like member positioned adjacent the drive side of the impeller to effect adjustment of cutting tolerances in cutting elements positioned between the impeller and plate-like member. The invention further includes a seal mechanism configured and positioned to retain the seal height of the seals throughout continuous adjustment of the impeller.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a non-provisional application claiming priority to provisional patent application Ser. No. 60/489,053 filed Jul. 22, 2003. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to centrifugal pumps of the type known as chopper pumps, and specifically relates to an improved means of axially adjusting the clearances between the pump elements as the elements wear. 
   2. Description of Related Art 
   Centrifugal pumps of the type known as chopper pumps are typically employed in processing fluids that contain solid waste materials, such as metal, plastics, municipal waste, animal byproducts, etc. Chopper pumps are structured with cutting elements that operate to chop or cut entrained solids in the fluid into a size that can be disposed of or processed further as needed. 
   Chopper pumps are typically characterized as having an impeller that is structured with vanes having cutting edges. The cutting edges of the vanes contact a cutting element positioned adjacent the vanes of the impeller to exert a cutting or chopping action on the solid material as it enters the pump. A very close cutting clearance is maintained between the vanes of the impeller and the cutting element to assure proper cutting action on the solids. However, with extended use of the pump, the solids begin to wear down the cutting element and/or the vanes of the impeller such that a gap begins to form between the cutting element and vanes of the impeller. It is critical to the efficiency of the pump to assure that the clearance between the structures is maintained at an appropriate distance or tolerance to optimize cutting action on the solids. 
   Some chopper pumps are also structured with impellers that have expeller or pump out vanes positioned on the back or drive side of the impeller to assure that solid or stringy material does not get caught between the back side of the impeller and the pump casing, or back plate that may be positioned between the pump casing and the impeller. Additional cutting elements may also be provided on the back side of the impeller to help cut the solids into smaller sizes so that they can be expelled from behind the impeller and not interfere with rotation of the drive shaft. Again, with extended operation of the pump, solids that may infiltrate behind the impeller eventually wear down the cutting elements and/or the expeller vanes, and the clearance between the cutting elements increases with wear. The clearance must then be adjusted to close the gap in order to maintain optimum cutting efficiency behind the impeller. 
   Conventionally known chopper pumps provide various means for adjusting the pump elements to provide closer cutting clearances. For example, some chopper pumps are adjusted by the insertion of selected sizes of shims between parts of the pump, thereby moving one element closer to another. In other known pumps, adjustment screws are employed. The known adjustment means employed in conventional chopper pumps, however, require the volute casing of the pump to be moved in relationship to the drive casing or bearing frame, or that the volute casing be moved relative to the suction casing, or both the suction casing and drive casing. 
   Conventionally known adjustment means result in a required change in the mounting dimensions of the pump feet or modification of the piping connection dimensions of the pump, or both. Consequently, the pump must be loosened from its base and some re-alignment performed, either in the drive or piping connections. In lieu of making such re-alignments, the connections must absorb the resulting movement within tolerated levels. Most importantly, such adjustments require that the pump be shut down to effect the required modifications, which translates into increased operation costs. 
   In addition to the above-noted difficulties that are inherent with conventional adjustment means or devices, movement of the impeller and drive shaft in conventional pumps is ultimately limited because of the sealing mechanisms of the drive shaft. That is, known pump designs have fixed seals about, or associated in some manner with, the drive shaft. Consequently, as the drive shaft is axially adjusted by known methods, the seal working height is also adjusted to the ultimate detriment of the seal and the life of the sealing mechanism is compromised. 
   Thus, it would be advantageous in the art to provide a centrifugal chopper pump having adjustment means for modifying the cutting clearances between the pump elements such that the adjustment can be effected without having to modify the pump connections or dimensions, without compromising the sealing mechanism and without having to shut down the operation of the pump. 
   BRIEF SUMMARY OF THE INVENTION 
   In accordance with the present invention, adjusting apparatus is provided for adjusting the cutting clearances between cutting elements of a centrifugal pump, particularly of the chopper type, in a manner which allows the clearance adjustments to be made without having to modify any of the connections or dimensions of the pump, which preserves the mechanical seals of the drive mechanism and which allows the adjustments to be made while the pump is in operation. 
   The adjusting apparatus of the present invention generally provides first adjusting structure for axially adjusting the impeller relative to a chopping element positioned at the suction end of the pump, and second adjusting structure for axially adjusting cutting elements located at the drive side of the pump to bring the cutting elements into closer clearance with the drive side of the impeller. 
   The first adjusting structure is configured and positioned to effect an axial movement of the drive shaft to consequently effect an axial movement of the impeller. The first adjusting structure is constructed in a manner that allows the drive shaft to be axially adjusted relative to the drive casing or bearing frame through which the drive shaft extends without having to disassemble the pump or readjust the bearings or seals associated with the drive shaft. In one exemplary embodiment described herein, the drive shaft is axially adjustable relative to the bearing frame through which it extends by providing a bearing cap that is secured to the drive shaft and is axially adjustable relative to the bearing frame. 
   The second adjusting structure is configured and positioned to effect axial movement of cutting elements located at the drive side of the pump to bring the cutting elements into closer tolerances with the drive side of the impeller. The cutting elements at the drive side of the pump may be provided on an axially movable plate element that is associated with the pump casing of the pump and which is positioned adjacent to the drive side of the impeller. 
   A particularly suitable embodiment of the invention includes a back plate that is positioned between the bearing frame and drive side of the impeller and is provided with cutting elements that interact with the impeller to provide a cutting of solids on the drive side of the impeller. The back plate is also preferably structured to house a sealing mechanism that is movable with the drive shaft so that the sealing height is maintained. A housing for the movable sealing mechanism may, however, be separately provided from the back plate itself, but may preferably be adjustable with the back plate in accordance with the present invention. 
   It is particularly suitable that, in the present invention, bearings and seals that are associated with the drive shaft are movable concurrently with the axial movement of the drive shaft and back plate to permit adjustment of the drive shaft and cutting elements during operation of the pump. The ability of the seals and bearings to move axially with the drive shaft presents a particular advantage over known chopper pump designs by eliminating the need to effect further adjustments of the bearings, seals or casing segments of the pump casing. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     In the drawings, which illustrate what is currently considered to be the best mode for carrying out the invention: 
       FIG. 1  is a view in longitudinal cross section of a centrifugal pump of the chopper type employing the adjustment structures of the present invention; 
       FIG. 2  is an enlarged view of the first adjusting apparatus of the present invention; 
       FIG. 3  is an elevational view in partial cutaway of a chopper pump illustrating the positioning of the adjusting apparatus of the present invention; 
       FIG. 4  is an elevational view in partial cutaway of the pump housing, drive shaft and impeller of a pump illustrating the positioning of the first adjusting apparatus; 
       FIG. 5  is an elevational view in partial cutaway of the back plate and pump housing illustrating the positioning of the second adjusting apparatus; and 
       FIG. 6  is an enlarged view in cross section of the drive shaft sealing mechanism of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The adjusting apparatus of the present invention is structured to provide axial adjustment of the impeller cutting clearances, on both the suctions side and drive side of the impeller, and may be structured and configured in a number of different ways.  FIGS. 1–6  present merely one example of a centrifugal pump arrangement and merely one exemplar means of providing adjusting apparatus in the centrifugal pump shown. 
     FIG. 1  illustrates in longitudinal cross section a centrifugal chopper pump  10  employing the apparatus of the present invention. The centrifugal chopper pump  10  generally comprises a pump casing, shown here as further comprising a drive casing, or bearing frame  12 , a volute casing  14  and a suction casing  16 . The volute casing  14  is secured to the bearing frame  12  and the suction casing  16  is secured to the volute casing  14 . 
   A drive shaft  18  extends through the bearing frame  12  and is supported by a first bearing assembly  20  and at least one other drive shaft support  21 , which is illustrated here by way of example as a second bearing assembly  22 . The second bearing assembly  22  may be housed within a bearing cap  24  that, as shown, is adjustably secured to the end face  25  of the bearing frame  12 . Alternatively, the second bearing assembly  22  may be positioned within the bearing frame  12 . Further alternatively, the drive shaft support  21  may be a structural element separate from the second bearing assembly and may serve only as a support by which the drive shaft  18  is axially adjustable, as described further hereafter. 
   The drive shaft  18  further extends through the volute casing  14  to engage the impeller  26 , which is positioned within the volute casing  14 . The drive shaft  18  may also extend through a separate plate-like member  27  which may have cutting elements, as described further hereinafter. The separate plate-like member  27  shown in  FIG. 1  is a back plate  28  which is received within the volute casing  14  and is positioned between the drive side  30  of the impeller  26  and the bearing frame  12 . The back plate  28 , in this particular embodiment, is formed with an annular collar  32  which extends into the bearing frame  12  and serves to house a sealing mechanism  34 . An annular stuffing box  36  surrounds the drive shaft  18  and seats against the annular collar  32  of the back plate  28  to complete the sealing assembly. The back plate  28  may be of any other suitable design, configuration or arrangement. 
   The chopper pump  10  is further structured with an intake or chopper plate  40  which is positioned between the suction casing  16  and the volute casing  14 . The chopper plate  40  is structured with cutting members  42  which are oriented in the direction of the impeller  26 . The impeller  26  has at least one vane  44  which has a cutting edge  45 . Typically, a plurality of vanes  44  are provided as shown. The impeller  26  is positioned in very close tolerance to the chopper plate  40  to rotate in very close proximity to the cutting members  42  of the chopper plate  40 . As the solid material enters the pump  10  through the inlet  46 , the material entering through the chopper plate  40  is cut by the interaction of the cutting members  42  of the chopper plate  40  and the cutting edges  45  of the vanes  44 . The fluid and chopped solids are then directed by the impeller  26  to the volute  48  of the pump  10  and then out of the pump through the outlet  50 . 
   The pump  10  may also be structured with cutting elements  52  located in the region of the drive side  30  of the impeller  26  to further process solids that may infiltrate between the back side  30  of the impeller  26  and the back plate  28 . The cutting elements  52  may be located on the drive side  30  of the impeller  26 , on the back plate  28 , or both. The cutting elements  52  are structured and positioned to provide cutting action on the solids before the solids can reach the drive shaft  18  and interfere with the rotation of the drive shaft  18  or operation of the associated sealing mechanism  34 . 
   The interaction between the cutting members  42  and the vanes  44  of the impeller  26  to chop or cut solid materials in the influent eventually causes a wearing down of those elements such that a widening gap begins to form between the cutting edge  45  of the vanes  44  and the cutting members  42  of the chopper plate. When the clearance between those parts increases, the vanes  44  and cutting members  42  become inefficient or ineffective at cutting the solids. 
   Likewise, with extended pump operation, the cutting elements  52  on or near the drive side  30  of the impeller  26  become worn and a widening gap begins to form between the cutting elements of the impeller  26  and/or the back plate  28 . Again, cutting efficiency is reduced and pump operation is compromised. It then becomes necessary to reduce the widened clearances between cutting parts to bring them into close proximity again to assure efficient cutting. 
   The present invention provides an improved means of adjusting the cutting parts of the pump to reduce the widened clearances caused by wear. A first adjusting apparatus  60  is provided to adjust the impeller  26  relative to the chopper plate  40 , thereby adjusting the clearance between the cutting edge  45  of the vanes  44  of the impeller  26  and the cutting members  42  of the chopper plate  40 . In the exemplar embodiment shown in  FIGS. 1 and 3 , the first adjusting apparatus  60  may comprise at least one adjusting screw  62  which extends through a flange  63  of the bearing cap  24  and contacts the end face  25  of the bearing frame  12 . 
   As shown in larger scale in  FIG. 2 , the adjusting screw  62  is threaded through the flange  63  of the bearing cap  24  and the inward end  64  of the adjusting screw  62  contacts the end face  25  of the bearing frame  12 . The adjusting screw  62  is formed with a hollow center  65  to receive an attachment screw  66  therethrough. The attachment screw  66  extends through the center  65  of the adjusting screw  62  and is threadingly secured into the end face  25  of the bearing frame  12 . When the bearing cap  24  is secured to the bearing frame  12  at initial operation of the pump  10 , the bearing cap  24  is positioned relative to the bearing frame  12  so that a gap  68  exists between the bearing cap  24  and the bearing frame  12 . 
   As the cutting edge  45  of the vanes  44  of the impeller  26  and the cutting members  42  of the chopper plate  40  become worn, and the clearance between those cutting elements widens, the impeller  26  may then be axially adjusted in a direction indicated by arrow  70  ( FIG. 1 ) toward the chopper plate  40  to reduce the widened clearance. This is accomplished by slightly loosening the attachment screws  66 , as shown in  FIG. 2 , and then rotating the adjusting screws  62  to bring the bearing cap  24  into closer proximity to the bearing frame  12 , thereby reducing the dimension of the gap  68  therebetween. The attachment screws  66  are then rotated again to secure the head  72  of each attachment screw  66  against the head  74  of the respective adjusting screw  62  through which it extends, thereby securing the adjusting screw  62  in place, as shown in  FIGS. 3 and 4 . 
   As may be best appreciated by reference to  FIG. 4 , movement of the bearing cap  24  by virtue of the adjusting screws  62  causes the drive shaft  18  to move in the direction of arrow  70 . The drive shaft  18  remains in place relative to the second bearing assembly  22  since the bearing cap  24  moves with the drive shaft  18 . Referring again to  FIG. 1 , bearings  73  of the first bearing assembly  20  are connection to the drive shaft  18  and move axially with the drive shaft  18  when adjusted. A space  75  is provided in the bearing frame  12  to permit axial movement of the bearings  73  in the direction of arrow  70 . A ring seal  76  is positioned in the bearing frame  12  to retain a comprehensive seal of the first bearing assembly, and is of a type that allows movement of the drive shaft  18  relative thereto while preserving the seal. 
   It should be noted that while the invention has been described thus far with the bearing cap  24  acting as a drive shaft support  21 , it is equally possible to provide a drive shaft support  21  that is not also a housing for a bearing assembly, but which is nonetheless positioned relative to the bearing frame  12  so that the first adjustment apparatus is positioned between the drive shaft support  21  and the bearing frame  12  to effect movement of the drive shaft  18  via the drive shaft support  21  in a manner as previously described. 
   Movement of the drive shaft  18  in the direction of arrow  70  causes the impeller  26  to move into closer proximity to the chopper plate  40 . Adjustment of the impeller  26  relative to the chopper plate  40  consequently results in an adjustment of the impeller  26  away from the back plate  28  in the direction of arrow  70 , thereby causing an increased gap or clearance between the cutting elements  52  of the impeller  26  and/or the back plate  28 . Hence, axial adjustment between the back plate  28  and the impeller  26  must be effected at the same time as the axial adjustment between the impeller  26  and the chopper plate  60  to bring the back plate  28  into proximity again with the impeller  26  so that the cutting elements  52  associated therewith will operate efficiently to cut the solid material. The present invention, therefore, provides second adjustment apparatus  78  for axially adjusting the back plate  28 , as illustrated in  FIGS. 1 ,  3  and  5 . 
   The second adjustment apparatus  78  further may be structured in a manner similar to the first adjustment apparatus  60  as previously described. Accordingly, at least one adjustment screw  80 , and preferably a plurality of adjustment screws  80 , is threadingly received through the front face  82  of the bearing frame  12 . Each adjustment screw  80  has an inward end  84  which registers against the drive side  86  of the back plate  28 . The adjustment screw  80  is formed with a hollow center shaft through which an attachment screw  88  is slidingly positioned. The attachment screw  88  is threadingly secured into the drive side  86  of the back plate  28 . 
   To adjust the back plate  28  after the impeller  26  has been axially adjusted, the attachment screw  88  is loosened by unscrewing it from the back plate  28 . The adjustment screw  80  is then rotated to move the back plate  28  in the direction of arrow  70  toward the impeller  26 , thereby reducing the clearance between the back plate  28  and the impeller  26 . When the back plate  28  has been axially moved by the required amount to provide a close tolerance between the cutting elements  52 , the attachment screw  88  is then secured against the adjustment screw  80  to secure the back plate  28  in place. 
     FIG. 6  illustrates in further detail an exemplary sealing mechanism  34  of the present invention which facilitates axial adjustment of the impeller  26 . The sealing mechanism  34  may comprise a rotating seal housing  90  which houses a rotating seal member  92 . The sealing mechanism  34  further comprises a stationary seal member  94  and a spring element  96  which is biased against the stationary seal member  94 . As the drive shaft  18  and impeller are axially adjusted in the direction of arrow  70 , the rotating seal housing and rotating seal member  92  move with the drive shaft  18  and the spring element  96  expands to retain a sealing engagement between the rotating seal member  92  and the stationary seal member  94 . 
   As the back plate  28  is axially moved in the direction of arrow  70  following adjustment of the drive shaft  18 , the stuffing box  36  moves with the back plate  28 , to which it is secured. The stationary seal member  94  is also caused to move with the annular stuffing box  36 . The spring element  96  is compressed again with movement of the annular stuffing box  36  to retain the seal face between the rotating seal member  92  and the stationary seal member  94 . Thus, it can be appreciated that the exemplary sealing mechanism  34  construction enables the appropriate amount of axial adjustment to be achieved between the impeller  26  and the chopper plate  40 , and between the back plate  28  and the impeller  26 , while retaining the seal height of the sealing mechanism  34 . Additionally, the exemplary structure enables the axial adjustment of the impeller  26  and back plate  28  to be effected without having to disassemble the pump or readjust or recalibrate any of the connections of the pump. 
   Adjustment of the cutting clearances as provided by the present invention can be effected with precision. For example, it may be desirable that the cutting clearances on both the suction side and drive side of the impeller  26 , as previously described, are set at 0.010 inch. Therefore, the adjustment screws  62 ,  80  may be structured with a visible indicia that represents a defined measurement of axial movement so that movement of the adjustment screws  62 ,  80  achieve the desired amount of axial adjustment. For example, the adjustment screws  62 ,  80  are illustrated as having hex heads, and the hex heads of the screws may be manufactured so that each flat surface of the head represents a revolution of the screw sufficient to achieve a 0.010 inch adjustment. 
   Thus, when axial adjustment of the cutting clearances is required, the attachment screws  66  and  88 , respectively, are loosened. The adjustment screw  62  is turned in the manner previously described until the impeller  26  contacts the chopper plate  40 . The position of the hex head of the adjustment screw  62  is noted and then rotated back by one flat of the head, which adjusts the impeller  26  away from the chopper plate  40  by 0.010 inch. The attachment screw  66  is then secured as previously described. Similarly, the adjustment screw  80  of the second adjustment apparatus  78  is turned until the back plate  28  contacts the impeller  26 . The position of the hex head of the adjustment screw  80  is noted and then turned by one flat of the head to adjust the back plate  28  away from the impeller  26  by 0.010 inch. The attachment screw  88  is then tightened to secure the back plate  28  in position. Again, the described adjustment amount of 0.010 inch is by way of example only and other adjustment measurements, as well as adjustment calibration means, may be employed with the invention. 
   While it may be preferred to effect adjustment of the impeller and the back plate in the manner described while the pump is not in active operation or use (i.e., not pumping fluid), the present invention allows the necessary adjustments to be made while the pump is in operation. Consequently, the present invention provides an improved means of adjusting the cutting parts of the pump as compared with known adjustment means. 
   The adjustment apparatus of the present invention is described herein with respect to a centrifugal pump of the chopper type and is particularly suited for such pumps. However, the adjustment apparatus of the present invention may be adapted for use in other types or configurations of centrifugal pumps where axial adjustment of the impeller relative to suction side and drive side elements of the pump casing are required. Thus, reference herein to particular details of the pump and the structure of the adjustment, apparatus of the invention are by way of example, and not by way of limitation.

Technology Classification (CPC): 5