Patent Publication Number: US-6988870-B2

Title: Casing for a centrifugal pump

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to centrifugal pumps of the type used in industrial processing of abrasive slurries, and is specifically related to pump casings which are structured to withstand high abrasive wear. 
     2. Description of Related Art 
     Centrifugal pumps are commonly used in a variety of industries to process liquid mixtures containing particulate solids, commonly known as slurries. The mineral processing and dredging industries are common examples of applications in which centrifugal pumps are used to process slurries. Centrifugal pumps used in such applications are subject to severe erosion and wear by the particles in the slurry flow, which leads to the need to repair or replace the pump. Substantial economic consequences result. Therefore, considerable effort is expended by pump manufacturers and users to try to ameliorate the problem of wear in centrifugal pumps. 
     Centrifugal pumps generally comprise an impeller housed within a casing. An inlet in the pump casing directs fluid into the rotating impeller. The rotation of the impeller ejects the fluid outwardly toward the volute of the pump casing and eventually through an outlet formed in the pump casing. The pump casing therefore provides a pressure vessel which serves the dual function of collecting the slurry expelled by the impeller and converting the high kinetic energy flow at the impeller exit into potential (i.e., pressure) energy at the discharge outlet of the pump casing. 
     The pump casing of a conventional centrifugal pump is further comprised, in general, of a volute, a drive side liner and a suction side liner. In some pump casing constructions, the volute and one of the sides (either the drive side or suction side) are integrally formed as one piece and are joined to a separate side liner in a two piece construction. In other pump casing constructions, the volute is a separate piece from the two side liners and are all joined together in a three piece construction. 
     While the particular shape of the casing may vary by manufacturer and specific application, pump casing side liners are universally configured with a circular peripheral edge which joins to the volute of the pump casing. The diameter of the side liner or liners is selected to permit movement of the impeller into and out of the pump casing to thereby facilitate assembly and maintenance of the pump. 
     With continuous use of centrifugal pumps in the processing of abrasive slurries, wear will occur within the pump casing at the periphery of the impeller near the cutwater of the pump. The cutwater is that internal portion of the pump casing that is adjacent the discharge of the pump in the direction of rotation of the impeller. The most significant wear occurs at the cutwater because of the interaction of the flow streams around the impeller shrouds, the discharge neck of the casing and the cutwater. Typically, the greatest wear occurs between the drive side liner and the volute of the casing at or near the cutwater. When sufficient damage has occurred that the integrity of the casing is compromised, the pump casing, or even the entire pump, must be replaced. 
     Changes in the shape of the pump casing have been employed in the past in an attempt to ameliorate the wear on the casing. For example, the shape of the volute, or the shape of the casing at the cutwater, has been modified to compensate for the wear. More specifically, the radius of the pump at the cutwater (as measured from the center line of the pump radially toward the cutwater) has been increased to direct the wear more toward the side wall of the pump casing. However, modifications in the pump casing often compromise pump performance and a trade-off occurs where pump efficiency may be sacrificed in the interest of reducing or re-directing the wear. 
     Thus, it would be advantageous in the art to provide a pump casing design which reduces loss in pump efficiency while directing wear to the side liners of the pump so that wear can be localized, thereby reducing repair costs. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, a pump casing for a centrifugal pump is configured with an open cutwater structure and at least one side liner that has a perimeter edge which is non-circular and having a portion with an increased radial distance at that point of the side liner positioned adjacent or near the cutwater of the pump to direct wear to the side liner. The particular configuration of the side liners provides for improved pump casing design and better pump efficiency, while reducing the attendant cost of repair and maintenance. 
     In accordance with the present invention, at least one side liner of the pump casing is formed with a perimeter edge for positioning against the volute section of the casing. The side liner has at least one portion, for orientation toward the cutwater of the pump casing, which is non-circular. The non-circular portion of the side liner oriented toward the cutwater of the pump casing may, in one embodiment, be configured with a radius of curvature distinct from the radius of curvature of the remaining portion of the side liner. The side liner of the present invention may also be described as having a radially extended portion oriented toward the cutwater of the pump casing which has a radially extending distance greater than a radius of the remaining portion of the side liner. 
     The radially extending or non-circular portion of the side liner provides an extended area of the side liner that is located in that area of the casing, near the cutwater of the pump casing, which is known to be prone to severe wear and gouging from the processing of abrasive slurries. Thus, the unique configuration of the side liner of the present invention assures that the wear will be localized on the side liner and not on the volute section of the pump casing so that only the side liner need be replaced when worn. The volute section of the pump casing is configured, consistent with the unique configuration of the side liner, to accommodate attachment of the side liner to the volute section. 
     The configuration of the pump casing of the present invention facilitates movement of the impeller into and out of the pump casing for ease of assembly and maintenance. Moreover, the configuration of the pump casing directs the abrasive wear to be localized on the side liners, thereby necessitating only the replacement of the side liners. The costs of operation are consequently reduced. 
    
    
     
       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 radial cross section of a prior art pump illustrating three piece construction of the pump casing; 
         FIG. 2  is a partial view in radial cross section of a prior art pump illustrating two piece construction of the pump casing; 
         FIG. 3  is a partial view in radial cross section of a prior art pump illustrating an alternative two piece construction of the pump casing; 
         FIG. 4  is a view in radial cross section of a prior art centrifugal pump casing, with the impeller removed, illustrating the typical location of abrasive wear; 
         FIG. 5  is a representational view in elevation of a prior art centrifugal pump casing illustrating the typical location of abrasive wear; 
         FIG. 6  is a representational view in elevation of a prior art centrifugal pump casing have a conventionally-shaped volute; 
         FIG. 7  is a representational view in elevation of a prior art centrifugal pump casing having a substantially dual radius configuration; 
         FIG. 8  is a representational view in elevation of a prior art centrifugal pump casing having an open cutwater configuration; 
         FIG. 9  is a view in elevation of the pump casing of the present invention, some elements shown in phantom; and 
         FIG. 10  is a partial view in cross section of the pump casing shown in  FIG. 9  taken at line  10 — 10  illustrating an alternative embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     By way of background description of the present invention,  FIG. 1  illustrates the general elements of a centrifugal pump  10 , which comprises a pump casing  12  and an impeller  14 . The pump casing  12  is structured with an inlet  16  through which fluid is introduced into the interior  18  of the pump casing  12 . The pump casing  12  is also structured with an outlet or discharge  20  through which fluid exits the pump casing  12 . The interior  18  of the pump casing  12  is structured and sized to house the impeller  14 . 
     Pump casing  12  designs and configurations vary widely among types of pumps and manufacturers. However, pump casings  12  are typically comprised of a volute section  24 , a suction side  26  and a drive side  28 . The suction side  26  has the inlet  18  formed therethrough, while the drive side  28  has an opening  30  through which the drive shaft  32  of the impeller  14  extends. The impeller  14  rotates about an axial center line  34  of the pump casing  12 . As better shown in  FIG. 5 , the discharge  20  may typically extend tangentially from the circular volute section  24  of the pump casing  12 . 
       FIG. 1  illustrates that in one typical construction of a centrifugal pump  10 , the volute section  24  may be separate from, and connected to, a suction side liner  36  and a drive side liner  38 . As shown in  FIG. 2 , a centrifugal pump  10  may alternatively be configured with the volute section  24  being integrally formed with the suction side  26  while a separate drive side liner  38  is connected to the volute section  24 .  FIG. 3  illustrates another alternative construction of centrifugal pumps  10  where the drive side  28  is integrally formed with the volute section  24  of the pump casing  12  while a separate suction side liner  36  is connected to the volute section  24 . 
     As illustrated more fully in  FIG. 5 , the side liners, here showing the drive side liner  38 , have a perimeter edge  40  where the side liner connects to the volute section  24  of the pump casing  12 . In all known embodiments of centrifugal pumps, the radius R of the side liner  38 , as measured from the axial center line  34  of the pump to the perimeter edge  40 , is consistent through the circumference of the side liner (i.e., the perimeter edge  40  is circular). Notably, the suction side liner, which is not specifically shown in  FIG. 5 , also has a perimeter edge which is also circular in all known embodiments of centrifugal pumps. The circumferential dimension of the perimeter edge  40  of the drive side liner  38  may vary between pump configurations and sizes, but is conventionally large enough to accommodate movement of the impeller therethrough. 
     One of the major problems with conventional pump casing configurations as previously described is that wear often occurs in the interior  18  of the pump casing  12 , as shown in  FIG. 4 , at the periphery  44  ( FIG. 1 ) of the impeller  14  near the cutwater  50  ( FIG. 5 ) of the casing  12 . This typical wear, designated at  52  in  FIGS. 4 and 5 , occurs because of an interaction of the flow streams around the impeller shroud  54  ( FIG. 1 ), the discharge neck  56  ( FIG. 5 ) and the cutwater  50  ( FIG. 5 ). Because of the location of the localized wear  52  gouge, it is not uncommon to have to replace the whole pump casing  12  prematurely, even though the volute section  24  and drive side liner  38  may only be partially worn. 
     A number of different pump casing shapes have been commonly employed to minimize wear in slurry pumps. These include the shapes shown in  FIGS. 6–8 . Specifically,  FIG. 6  shows a conventional volute type configuration where the volute section  24  of the pump casing  12  in the area of the cutwater  50  extends more inwardly toward the axial center line  34  such that the cutwater radius R C , defined as extending from the axial center line  34  to the cutwater  50  of the casing  12 , is a comparatively shorter distance. 
       FIG. 7  illustrates a pump casing configuration that may be designated as a “double circle” where the curvature of the volute section  24  in the area of the cutwater  50  is greater than the conventional volute type pump casing design, resulting in a cutwater radius R C  that is greater than the cutwater radius R C  in a conventional volute type pump design as shown in  FIG. 6 .  FIG. 8  illustrates another pump casing configuration where the curvature of the volute section  24  in the area of the cutwater  50  is less than the “double circle” type design shown in  FIG. 7 , and the resulting cutwater radius R C  is even greater than the cutwater radius R C  of the “double circle” type design. The pump casing configuration shown in  FIG. 8  may be referred to as having an open cutwater design. 
     The optimum choice of pump casing configuration depends on the required efficiency and the most likely operating flow of the pump relative to its Best Efficiency Point (BEP) flow. It is reasonably well known that using a conventional volute type casing, as shown in  FIG. 6 , at low relative flows produces high wear behind the cutwater, despite the fact that the conventional volute type design is the most efficient configuration. As the cutwater radius Rc of the pump increases (transitioning from volute type ( FIG. 6 ) to open cutwater type ( FIG. 8 ), the wear point moves away from the cutwater and more to the side wall as shown previously in  FIG. 4 . 
     The open cutwater design of the pump casing is the most forgiving design and is able to operate over wide flow ranges (w.r.t. BEP) without significant wear at the cutwater itself. This design also has the broadest band of high efficiency, even though the peak efficiency is usually lower than that of the volute type casing. However, the problem with the open cutwater design has traditionally been that the side of the casing is frequently gouged by wear, as shown in  FIG. 4 . That fact has lead to premature replacement of the casing when the majority of the casing may still be near full thickness. The present invention aims to reduce the need for expensive casing replacement by providing a novel casing configuration which ensures that wear occurs on the side liner and not on the volute portion of the casing. Therefore, only the side liner needs to be replaced, making repairs much more economical. 
     The pump casing  80  of the present invention is shown in  FIG. 9  where like parts of conventional pump structure, as previously described, are referenced by the same numerals. The pump casing  80  is comprised of a volute section  24  that has an outer peripheral profile, defined as extending from the cutwater  50  to the discharge neck  56 . The pump casing  80  has the peripheral profile of an open cutwater design. The pump casing  80  also has at least one side liner  82  that has an outer perimeter  84 , at least a portion of which is non-circular. The side liner  82  is, therefore, configured with a radially extending portion  86 , oriented toward the cutwater  50  of the pump casing  80 , which is designed to localize wear on the side liner  82 . The volute section  24  of the pump casing  80  is similarly configured to accommodate attachment of the side liner  82  to the volute section  24  (i.e., the volute section has a non-circular opening sized or shaped to accommodate attachment of the perimeter edge of the side liner to the opening of the volute section). 
     The exact perimeter configuration or shape of the side liner  82  may vary considerably, but generally is comprised of a portion having a non-circular perimeter edge and a radially extending portion which is positioned to bear the wear caused by abrasive slurries. By way of example only,  FIG. 1  depicts one possible configuration of a pump casing  80  of the present invention. It should also be noted that pump casing  80  may be of a two-piece or a three-piece construction as previously described and illustrated in  FIGS. 1–3 . It should also be noted that where the pump casing is of three-piece construction, one or both of the separate side liners may be configured in the manner of the present invention. 
     The pump casing  80  has an axial center line  34  (extending into the paper) about which the impeller  14  rotates. The pump casing  80  also has a radial center line  88  normal to the axial center line  34  and parallel to a discharge center line  90  formed through the center of the discharge  20  of the pump casing  80 . The distance between the radial center line  88  and discharge center line  90  may be defined as L O . The pump casing  80  may be said to have a base radius R B  defined by the line extending from the axial center line  34  to the point A B  on the peripheral profile of the casing  80  through or near the radial center line  88 . 
     The perimeter  84  of the side liner  82  may be structured with a portion  92  which is circular in the conventional fashion. As illustrated by way of example only in  FIG. 9 , the portion  92  of the perimeter  84  which is circular may extend from point T 1  to point T 2  on the perimeter  84 , extending in an arc of approximately 240° (counterclockwise) about the axial center line  34 . The circular portion  92  of the perimeter  84  may be greater or lesser than illustrated. The side liner  82  may thus be said to have a radius R S  extending from the axial center line  34  to the circular perimeter  92  of the side liner  82 . 
     In the present invention, the base radius R B  of the pump casing  80  is greater than the radius R S  of the side liner  82 . The radius R S  of the side liner  82  is also greater than the radius R I  of the impeller, which extends from the axial center line  34  to the circumferential edge  94  of the impeller  14 . Therefore, the impeller  14  can be moved into and out of the pump casing  80  through the side liner  82  to facilitate assembly, repair and maintenance of the pump. 
     The radially extended portion  86  of the side liner  82  is oriented toward the cutwater  50  of the pump casing  80  and may have any shape or configuration which assures that wear is localized to the side liner  82 . As illustrated by way of example in  FIG. 9 , the radially extending portion  86  may be configured with an apex  100  positioned in close proximity to the cutwater  50 . The radially extending portion  86  may be defined by a tangential line  102  extending from the perimeter  84  of the side liner  82  at point T 1  to a point A P  near the apex  100  of the side liner  82 , and then by a curved line from point A P  to point T 2  on the perimeter  84  of the side liner  82 . The distance D P  from the axial center line  34  to the apex  100  or to the point A P  on the pump casing  80  is greater than the radius R S  of the side liner  82  and may preferably be greater than the base radius R B  of the pump casing  80 . 
     The pump casing  80 , as previously noted, is of an open cutwater design. Specifically, the peripheral profile of the pump casing  80  in the area of the cutwater  50  may be defined by a tangential line  104  extending from point A B  at the radial center line  88  of the pump casing  80  to a point A C  at the discharge neck  56  of the casing  80 . The volute section  24  of the pump casing  80  in the area of the cutwater  50  is similarly configured to accommodate attachment of the uniquely configured side liner  82  to the volute section  24  of the casing  80 . The perimeter  84  of the side liner  82  may preferably be positioned a selected distance Y from the periphery of the pump casing  80 , the distance Y being defined between tangential line  102  and tangential line  104 . Further, the distance D C  between the axial center line  34  and the point A C  at the cutwater  50  is equal to, but preferably greater than the base radius R B  of the casing  80 . 
     Again, the particular shape or configuration of the radially extending portion  86  of the side liner  82  may vary considerably, dependent on the size of the pump, the size or dimensions of other elements of the pump (e.g., the impeller), the particular types of slurries being processed, and other factors. However, using the particularly illustrated embodiment of the invention, the following table provides a few exemplary variations on the illustrated dimensions that may be employed in structuring a pump casing of the present invention. 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
               
                   
                 Variable 
                 Minimum 
                 Maximum 
                 Preferred 
               
               
                   
                   
               
             
            
               
                   
                 D C   
                 R B   
                 2.0 R B   
                 1.2 R B   
               
               
                   
                 Y 
                 0 
                 R B   
                 R B –R S   
               
               
                   
                 R B   
                 1.05 R I   
                 2.0 R I   
                 1.3 R I   
               
               
                   
                 R S   
                 R I   
                 0.95 R I   
                 1.05 R I   
               
               
                   
                 L 0   
                 0 
                 2.5 R B   
                 1.2 R B   
               
               
                   
                 D P   
                 R S   
                 3.0 R B   
                 1.2 R B   
               
               
                   
                   
               
            
           
         
       
     
     The pump casing  80  of the present invention may be manufactured from any of the known conventional wear resistant materials, such as hard metal alloys or even elastomers (e.g., rubber). In an alternative embodiment of the invention, the pump casing  80  may further be structured with a wear resistant insert  110 , as shown in phantom in  FIG. 9  and as further illustrated in  FIG. 10 . The wear resistant insert  110  is located in the radially extending portion  86  of the side liner  82  and is particularly positioned in that area which is known to be most vulnerable to wear, as previously illustrated in  FIG. 4 . The wear resistant insert  110  may be made of any suitable material, such as a ceramic, that is particularly resistant to abrasive wear. The side liner  82  may be structured so that the insert  110  alone may be replaceable when worn, or may be formed such that the insert  110  is more integral to the side liner  82  so that the side liner  82  is replaceable when the insert  110  becomes worn. 
     The pump casing of the present invention is particularly configured to direct wear to a replaceable side liner or portion of side liner when worn by the abrasive action of slurries being processed by the pump. The pump casing may be configured in a variety of ways consistent with the general objective of the structure as disclosed herein. Those of skill in the art will recognize the modifications that may be made to the pump casing of the present invention to adapt it to the specific needs of the application or the pump. Thus, specific reference to particular illustrations of embodiments of the invention are by way of example only and are not intended to limit the scope of the invention.