Abstract:
A pump impeller and associated cutting elements are disclosed which are especially designed and positioned near the periphery of the impeller to reduce the size of entrained solids in a pumped fluid, or slurry, and to expel such solids from the impeller, drive shaft and associated sealing mechanisms.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a non-provisional application claiming priority to provisional patent application Ser. No. 60/488,504 filed Jul. 18, 2003. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to centrifugal pumps of the type known as chopper pumps, which are structured to process fluids containing large-sized solids that must be cut or chopped by the pump. Specifically, this invention relates to an impeller and associated cutting elements which are configured to process entrained solids and exclude them from the area of the seal of the pump. 
   2. Description of Related Art 
   Centrifugal pumps of the chopper type are used in many and varied industries to process fluids that contain larger-sized solids, such as plastics or animal byproducts. Chopper pumps are typically characterized by having an impeller that is structured to contact a cutting element positioned adjacent the vanes of the impeller to exert a cutting or chopping action on the solid material entering the pump. The impeller and cutting structures positioned on the suction side of chopper pumps processes the majority of the solids content to a size that can be moved through the pump. However, some solids tend to also move toward the drive side of the impeller and may move inwardly toward the drive shaft of the pump. 
   When solids move toward the drive side, or back, of the impeller and inwardly toward the drive shaft, debris can become wrapped around the drive shaft and impede the operation of the pump. This is especially the case with fluids containing stringy solids. Debris behind the impeller can cause a build up in heat and wear on the impeller and can impede the cooling and lubrication of the seal elements. Solid material may infiltrate the seal and cause further problems with pump operation. Thus, some known chopper pumps have employed flushing mechanisms to clean behind the impeller. 
   Other known chopper pumps have used impellers designed with cutting elements located on or near the back side of the impeller and about the drive shaft to chop solid material in the location of the drive shaft. An example of an impeller and cutting element of the type described is disclosed in U.S. Pat. No. 5,460,482 to Dorsch. Some chopper pumps also use restrictor bushings around the shaft to keep larger solids away from the seal, as described in the &#39;482 patent to Dorsch. Yet other chopper pumps use an open impeller design to reduce pressure behind the impeller so that solids are not drawn toward the back side of the impeller. 
   Prior art chopper pumps which employ a cutting element on the back side of the impeller require that the cutting element be positioned adjacent the impeller hub and/or in very close proximity to the drive shaft. As such, debris in the fluid, especially stringy material, can infiltrate all the way to the drive shaft and seal assembly before any chopping or cutting of the material takes place. 
   Thus, it would be advantageous in the art to provide an impeller and cutting element configuration in a centrifugal chopper pump that processes and excludes debris from behind the impeller before the debris can reach the drive shaft and seal assembly, thereby improving pump operation and the life of the pump. 
   BRIEF SUMMARY OF THE INVENTION 
   In accordance with the present invention, an impeller and cutting elements are positioned relative to the drive shaft of the pump and are configured to interact in a manner that chops or cuts debris near the peripheral edge of the drive side of the impeller to effectively reduce and exclude debris from contact with the drive shaft and any associated sealing assemblies. While the impeller and cutting elements of the present invention are described herein with respect to use in centrifugal pumps of the chopper type, the impeller and cutting elements may be adapted for use in types of centrifugal pumps other than chopper pumps. 
   The present invention comprises an impeller, having a drive side oriented away from the inlet of the pump, which is particularly configured with cutting structures that interact with cutting elements positioned adjacent to the drive side of the impeller. The cutting structures particularly comprise cutting elements that are positioned toward the outer periphery of the impeller to provide chopping and cutting of solids near the periphery of the impeller. The peripherally-located cutting elements are also structured and placed to exclude the chopped debris from the drive side of the impeller, and especially away from the drive shaft and any associated sealing assemblies. 
   The impeller may also include debris excluding structure that is located nearer to the central axis of the impeller, toward a central opening of the impeller, to exclude any residual or errant solid debris from infiltrating beyond the peripherally-located cutting elements. The debris excluding structure positioned nearer to the central axis of the impeller may be configured as a labyrinth element positioned proximate the drive shaft to prevent debris from reaching the drive shaft and seals of the pump. 
   The present invention further comprises cutting structures that are positioned adjacent to the drive side of the impeller to interact with the cutting structures that are formed on the drive side of the impeller. The adjacently positioned, interacting cutting structures may form a part of the pump casing of the pump, such as a drive side casing or an end plate structure attached to the pump casing. 
   Alternatively, and as particularly described herein, the adjacently positioned cutting structures may be formed as part of a separate back plate that is positioned between the pump casing and the drive side of the impeller. Providing the adjacently positioned cutting structures on a separate plate-like structure, attachable to and separate from the pump casing, has the particular advantage of enabling removal of the back plate from the pump casing for ease of replacement when the cutting structures become worn. A particularly suitable back plate is described herein which is further structured to provide additional sealing of the drive shaft and sealing assemblies from any debris that may infiltrate the drive side of the impeller. 
   The impeller, with its cutting elements, and the interacting cutting elements provided on the pump casing or back plate comprise an impeller assembly of the present invention that may be adapted to various types of pumps. The impeller assembly of the present invention provides certain advantages to operation of the pump as will become more evident with a more complete description of the invention which follows. 

   
     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 illustrating the impeller assembly of the present invention; 
       FIG. 2  is a perspective and exploded view of the suction side of an impeller and back plate of a chopper pump in accordance with the present invention; 
       FIG. 3  is a perspective and exploded view of the drive side of an impeller and back plate of a chopper pump in accordance with the present invention; 
       FIG. 4  is a side view in elevation of a cutting element of the present invention; 
       FIG. 5  is a perspective view in partial cutaway of the impeller and back plate shown in  FIG. 2  when assembled within the pump; 
       FIG. 6  is a perspective and exploded view of the drive side of an alternative impeller embodiment of the present invention; and 
       FIG. 7  is an enlarged view of an alternative embodiment of a back plate cutting element for use with the impeller embodiment illustrated in  FIG. 6 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates in longitudinal cross section one exemplar configuration of a centrifugal chopper pump constructed with the impeller  10  and cutting elements  12  of the present invention. The centrifugal chopper pump  14  generally comprises a pump casing that is shown in  FIG. 1  as comprising a drive casing  16 , a volute casing  18  that is secured to the drive casing  16 , and a suction casing  20  that is secured to the volute casing  18 . 
   The drive casing  16  is generally structured to receive a drive shaft  22  which extends through the drive casing  16  and into the volute casing  18 . Bearing assemblies  24  and  25  are generally positioned within the drive casing  16  to support the drive shaft  22 . The drive shaft  22  extends through the drive casing  16  and is attached to the impeller  10 , which is positioned within the volute casing  18 . 
   The drive shaft  22  may also extend through a back plate  26  that is positioned between the drive casing  16  and impeller  10 . The back plate  26  is shown secured to an end wall  27  of the drive casing  16 , but may be secured to any suitable structure of the pump  14  or portion of the pump casing. The back plate  26  may be of any suitable configuration that provides adjacent positioning of cutting elements to interact with the impeller  10 , as described more fully hereinafter. The back plate  26  illustrated in  FIG. 1  is configured with an annular collar  28  that extends through the end wall  27  of the drive casing  16  and is structured to house a sealing mechanism  30  positioned about the drive shaft  22 . 
   In operation, fluid containing larger-sized solids enters into the pump  14  through an inlet  32  in the suction casing  20 . The fluid and solids enter through an intake or chopper plate  34  that is positioned between the suction casing  20  and the impeller  10 . As described more fully hereinafter, the impeller  10  interacts with the chopper plate  34  to cut and chop the solids in the fluid. The fluid and solids slurry then flows into the volute  36  of the pump  14  from where it is expelled through the outlet  38  of the pump  14 . 
   It can be appreciated from the view of  FIG. 1  that as the fluid and solids slurry moves into the volute  36 , the fluid has a tendency to impact the rear portion  40  of the impeller  10  where it rotates along the back plate  26 . It should be noted that the size, dimension and position of the impeller  10  and back plate  26  as shown in  FIG. 1  is merely by way of example to illustrate the structures of the invention, and the axial extension of the rear portion  40  of the impeller  10  into the volute  36  may not be as pronounced as illustrated in  FIG. 1 . Nonetheless, fluid and debris can move behind the impeller, and potentially infiltrate to the drive shaft  22  and sealing mechanism  30  of the pump  14 . Thus, the present invention provides a structured impeller assembly having associated cutting elements which are especially designed to providing cutting action of any debris that may initiate entry behind the impeller  10 . 
   A first embodiment of the impeller  10  of the present invention is illustrated in further detail in  FIGS. 2 and 3 .  FIG. 2  is a perspective view of the impeller  10  viewed from the suction side  48  and eye  50  of the impeller  10 . The impeller  10  is shown at a spaced distance from the back plate  26  of the pump to illustrate the detail of the back plate  26 .  FIG. 3  is a perspective view of the drive side surface  54  of the impeller  10  as shown spaced from the back plate  26 , the drive side view of which is also shown. 
   As seen in  FIG. 2 , the impeller  10  comprises a plurality of vanes  56  which radiate outwardly from the eye  50  of the impeller  10 . Each vane  56  has a cutting edge  57  that is positioned in close tolerance with the chopper plate  34  ( FIG. 1 ) to effect cutting of solids. In this particular embodiment of the invention, the impeller  10  is formed with a shroud  58  which is oriented to be positioned adjacent the back plate  26  when assembled in the pump. The vanes  56  extend axially outwardly from the shroud  58  in a direction away from the back plate  26 . The shroud  58  has a circumferential edge  60  which defines the periphery of the impeller  10  and which is oriented toward the volute  36  of the pump  14 . 
   As also seen in  FIG. 2 , the back plate  26  is structured with a disc-like front face  62  having a central opening  64  through which the drive shaft  22  extends to engage the impeller  10  ( FIG. 1 ). The back plate  26  has a circumferential edge  66  which is generally sized to be received within the volute casing  18 , as shown in  FIG. 1 . As best seen in  FIG. 3 , the back plate  26  is further structured with an annular collar  28  that extends into the drive casing  16 , as shown also in  FIG. 1 . The back plate  26  is also structured with holes  68  positioned to receive bolts or other securement means for securing the back plate  26  to the drive casing  16 . 
   Referring again to  FIG. 2 , the back plate  26  is provided with at least one cutting element  12  located near the circumferential edge  66  of the back plate  26 . Two cutting elements  12  are shown in the view of  FIG. 2 . The cutting elements  12  may be structured in the form of studs  72  having back plate cutter teeth  70 . In this embodiment, the studs  72  are received in recessed slots  74  formed in the front face  62  of the back plate  26 . The studs  72  are attached to the back plate  26  by appropriate securement means, such as a bolt  76 . The studs  72  are, therefore, replaceable when worn. Alternatively, however, the cutting elements  12  may be integrally formed with the back plate  26  and when worn, the back plate  26  may be replaced. 
   The studs  72  are most suitably hardened by known methods in the art to render them resistant to wear, thereby extending the service life of the back plate cutter teeth  70 .  FIG. 4  is a side view of a stud  72  showing more particularly that the stud  72  is formed with a body  78  portion and the back plate cutter teeth  70  extend outwardly from the body portion  78 . The body portion  78  is sized to be received in a recessed slot  74  of the back plate  26 . 
   Referring to  FIG. 3 , the impeller  10  is formed with a central opening  80  which is configured to receive the terminal end of the drive shaft  22 , as shown in  FIG. 1 . Radiating outwardly from near the central opening  80  may be a plurality of expeller vanes  82 . The expeller vanes  82  extend axially outward from the drive side surface  54  of the impeller  10  in the direction of the back plate  26 . The expeller vanes  82  are positioned and configured to facilitate the movement of fluid and solids away from the center of the impeller  10  near the drive shaft. 
   In the particular embodiment of the invention shown in  FIG. 3 , each expeller vane  82  is structured with indentations  84  near the periphery or circumferential edge  60  of the shroud  58 . The indentations  84  further define outwardly extending portions that form cutter teeth  86  on the drive side surface  54  of the impeller  10 . As best seen in  FIG. 5 , when the impeller  10  is positioned adjacent the back plate  26  in assembly of the pump, the cutter teeth  86  of the impeller  10  are positioned to move between the back plate cutter teeth  70  as the impeller  10  rotates relative to the back plate  26 . The impeller cutter teeth  86  are most suitably hardened to render them resistant to wear. 
   The interaction or meshing of the impeller cutter teeth  86  and the back plate cutter teeth  70  provides a cutting action on any debris that begins to infiltrate between the drive side surface  54  of the impeller  10  and the back plate  26 . The cutting action, most importantly, takes place at the periphery of the impeller  10  and back plate  26 , thereby reducing the likelihood that debris will infiltrate all the way to the center of the impeller  10  near the drive shaft. As noted before, the expeller vanes  82  further operate to exclude debris from behind the impeller  10 . 
   It should further be noted that the impeller cutter teeth  86  are illustrated here as being part of the expeller vanes  82  (i.e., in radial alignment or extension with the expeller vanes  82 ). However, cutter teeth  86  that extend axially from the shroud  58  may be formed near the periphery of the impeller in positions other than as a radial extension of the expeller vanes  82 , as long as they are positioned to mesh or interact with the back plate cutter teeth  70 . The impeller cutter teeth  86  may also be detachably attached members in a manner similar to the studs  72  on the back plate  26 . 
   The present invention further deters debris from infiltrating near the drive shaft  22  or the sealing mechanism  30  of the pump  14  by providing a debris excluding structure, shown as a labyrinth  90 , near the center axis of the impeller  10  and back plate  26 , as best seen in  FIG. 5 . The labyrinth  90  comprises a ring  92  which extends axially outwardly from the front face  62  of the back plate  26 . As best seen in  FIG. 3 , the impeller  10  is further configured with an annular channel  94  in which the ring  92  is received when the impeller  10  and back plate  26  are assembled in the pump ( FIGS. 1  and  5 ). The impeller  10  is further configured with an annular ring  96  surrounding the central opening  80  of the impeller  10  ( FIG. 3 ) which extends axially outward from the drive side surface  54  of the impeller  10 . 
   An annular shoulder  98  extends radially from the central opening  80  to the annular ring  96  of the impeller  10 . Thus, as best seen in  FIGS. 1 and 5 , any debris that may have infiltrated from the circumferential edge  60  of the impeller  10  or periphery toward the center of the impeller  10  is presented with a labyrinth  90  having four ninety degree turns through which the debris and fluid must move in order to reach the drive shaft  22  and the sealing mechanism  30 . Accordingly, the likelihood that any debris will reach the drive shaft  22  or sealing mechanism  30  is rendered very remote. 
   The invention has heretofore been described and illustrated in terms of an impeller  10  having a shroud  58 .  FIG. 6  illustrates an alternative embodiment of the present invention where the impeller  100  is open, or has no shroud. The impeller  100  in this embodiment has a plurality of vanes  56  which radiate outwardly from a central axis  102  of the impeller  100  and curve as they radiate from the central axis  102 . On the drive side surface  54  of the impeller  100 , each vane  56  may further be structured with an expeller vane  82  that extends axially in the direction of the back plate  26 . 
   Indentations  84  are formed near the periphery of the impeller  100  along the expeller vanes  82 , thereby providing impeller cutter teeth  86  positioned near the periphery of the impeller  100 . In this embodiment, the indentations  84  are curved, rather than linear as shown in the embodiment of  FIG. 3 . Correspondingly, the impeller cutter teeth  86  are curved as well. However, the indentations  84  and impeller cutter teeth  86  may be linear as previously described. 
   The back plate  26  in the embodiment shown in  FIG. 6  is essentially identical to the back plate  26  as previously described with respect to  FIGS. 2 and 3 . However, as shown in  FIG. 7 , the studs  104  are correspondingly configured to interact with the curved impeller cutter teeth  86  of the impeller  100 . Thus, the studs  104  are formed with curved cutter teeth  106  which are spaced from each other by a curved channel  108  which is appropriately configured and curved to receive the impeller cutter teeth  86  therein as the impeller  100  rotates against the back plate  26 . Again, studs  104  of the embodiment shown in  FIGS. 6 and 7  are hardened to resist wear, but are replaceable when worn. Alternatively, the back plate cutter teeth  106  of this embodiment may be integrally formed with the back plate  26  in the manner previously described. 
   The shroudless impeller  100  may also be configured with debris excluding structure near the central axis  102  of the impeller as previously described with respect to the embodiment of  FIGS. 2 and 3 . The debris excluding structure, again, may be a labyrinth  90  structure which comprises a series of annular rings  96  and indentations  94  which produce a plurality of angled turns that the debris and fluid must negotiate in order to reach the drive shaft of the pump. The debris excluding structure positioned more in proximity to the central axis  102  of the impeller  100  may, however, be any suitable structure or configuration that facilitates elimination of debris from near the drive shaft. 
   In normal operation, the interaction between the impeller cutter teeth  86  and the back plate cutter teeth  70 ,  106  cause an eventual wearing of both, and a gap forms between the interacting cutting elements. The impeller may then be axially adjusted relative to the back plate to lessen the gap between the impeller cutter teeth and back plate cutter teeth. Eventually with continued operation, however, the cutter teeth of both the impeller and the back plate become sufficiently worn so that the impeller must be replaced or the cutting elements on the back plate or on the impeller, or both, must be replaced. 
   The impeller assembly of the present invention, comprising the impeller with peripheral cutting structures and interacting cutting elements on the pump casing or on a back plate, is particularly suited for use in centrifugal pumps of the chopper type, but may be adapted for use in any type of centrifugal or slurry pump. Because the configuration of chopper pumps, and centrifugal pumps in general, vary widely, it will be apparent to those of skill in the art what modifications may be required to adapt the invention to various pumps. Thus, reference herein to particularly described or illustrated details of the invention are merely by way of example and not by way of limitation.