Abstract:
An improved impeller and a casing for a centrifugal pump are disclosed. The impeller comprises vanes which sweep an arc around an impeller axis to provide a smooth path past the impeller and through the pump. The casing is constructed to allow maximum flow rate at the eye of the impeller then shrink the flow channel to reduce internal recirculation promote efficiency, further limiting the effect of damaging forces. The impeller is suited for use in pumps in which a high head is required and in which only low shear forces must be applied to the fluid moving through the pump.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application makes reference to, claims priority to, and claims benefit from the U.S. Provisional Patent Application Ser. No. 61/931,369, filed Jan. 24, 2014. The above-identified application is hereby incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to centrifugal pumps, such as, for example, centrifugal pumps having impellers of radial, Francis vane, mixed flow, and axial flow design. More specifically, the present invention relates to an impeller and casing for centrifugal pumps that may produce a high head output and high efficiency, while also being capable of pumping shear sensitive liquids or liquids having suspended solids without applying damaging forces to the liquid or the solids. 
       BACKGROUND OF THE INVENTION 
       [0003]    Conventional centrifugal pumps include an impeller that rotates within a cavity in the body of the pump. Fluid entering from an inlet in the cavity typically flows toward the impeller and near to the impeller&#39;s center of its rotation. Further, the rotation of the impeller typically forces fluid to flow radially outward toward an outlet of the cavity that is often at a location that is radially adjacent to the impeller. 
         [0004]    Producing high head output by centrifugal pumps often requires that the impeller be rotated at accelerated speeds. However, such accelerated speeds are typically associated with the generation of a relatively significant shearing force that is applied to the fluid that is flowing through the pump. Yet such shearing forces may be unacceptable for at least certain types of fluids and/or solids that are passing through the pump. For example, food processing systems, pharmaceutical processing systems, and clay slurries, are examples of applications in which a high shearing force may be unacceptable due to the potential damage that such shearing forces may cause to the structure of the fluid and/or the solids within the fluid. Thus, in applications in which the fluid or solids flowing through the pump should not be subjected to such shearing forces, typically the impeller may be operated at a low pump speed and have a low head output. Moreover, to avoid and/or minimize the generation of such shearing forces, the total head generation capability of the centrifugal pumps may be limited or centrifugal pumps may not be used in such applications. 
         [0005]    Additionally, low shear centrifugal pump designs, particularly food grade pumps, have relatively lower efficiencies than standard industrial centrifugal pumps. Thus, low shear centrifugal pump designs often result in pumps that have more internal recirculation of fluids and/or solids within the pump and have higher power requirements. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The disadvantages and limitations of known impeller centrifugal pumps can be overcome by providing an impeller that subjects the fluid moving through the pump to lower shear forces than known centrifugal pump impellers. 
         [0007]    In particular, the vanes of the impeller, limit the forces applied to fluid flowing past the impeller. The vanes are configured to have a circumferential width and axial length that guides the fluid along a smooth path thereby avoiding the shearing forces associated with abrupt changes in the flow path of a fluid. Also, the longer fluid path reduces both the rate of acceleration and the intensity of jerk acceleration. 
         [0008]    The top of each vane of the impeller can have a wide cross section which creates an extended slip path from the high pressure side of the vane to the low pressure side of the vane. This extended slip path improves the efficiency of the impeller by reducing the amount of fluid that can move from the high pressure side of the vane to the low pressure side of the vane within the pump. Reducing fluid recirculation within the pump from the high pressure side of the vane to the low pressure side of the vane reduces the amount of shearing forces felt by the fluid. There is also a circular shroud as part of the bottom of the impeller. This shroud prevents recirculation from the high pressure side of the vane to the low pressure side. The rotation of the shroud imparts energy to fluid rotating within the volute and improves efficiency. 
         [0009]    In another aspect, disadvantages and limitations of known impeller centrifugal pumps can be overcome by providing a circular or volute casing that has a recess for part of the impeller that further restricts internal recirculation, and improves efficiency, by narrowing the flow chamber within the pump from the impeller eye to the periphery. The narrow flow chamber also increases priming capability. 
         [0010]    In another aspect, the rate of fluid acceleration and the incidence of abrupt changes in direction that can manifest as high pressure losses can be reduced resulting in higher inlet pressure requirements. Reduction of acceleration forces and reduction of abrupt changes in direction inherently results in a reduction of inlet pressure requirements. Further to the reduction of inlet pressure, the hub of the impeller can be diametrically tapered from maximum hub diameter at the center of the impeller height to a diameter equivalent to the impeller blade width. 
         [0011]    In yet another aspect, the outlet port of the casing can be positioned such that the aft location of the internal diameter of the port is aligned with the back of the impeller shroud to ensure an efficient flow rate as the fluid translates from the axial center front to the impeller to the rearward periphery of the same. 
         [0012]    Test results show that, when pumps employing the claimed impeller and casing are used in certain dairy processing applications, the acid degree value of the milk does not increase as a result of pumping. An increase in acid degree value typically serves as an indicator that the fat globules in the milk have been damaged due to mechanical shearing. Accordingly, the claimed impeller and casing cause less damage to the milk. This advantageous result would also benefit other applications beside dairy processing systems, such as food processing systems, pharmaceutical processing systems, and clay slurries. 
         [0013]    These and other objects and advantages of the impeller and/or casing described in this disclosure will be understood from the following description and drawings of exemplary embodiments of an impeller and casing. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         [0014]      FIG. 1  illustrates an isometric view of an embodiment of the inlet side of an impeller. 
           [0015]      FIG. 2  illustrates an inlet side view of the impeller shown in  FIG. 1 . 
           [0016]      FIGS. 3A and 3B  illustrate side elevation views of the impeller shown in  FIG. 1 . 
           [0017]      FIG. 4  illustrates an isometric view of the impeller shown in  FIG. 1 . 
           [0018]      FIG. 5  illustrates a rear view of an impeller according to an illustrated embodiment. 
           [0019]      FIG. 6  illustrates a side cross sectional view of a casing according to an illustrated embodiment. 
           [0020]      FIG. 7  illustrates a partial cross sectional view of an impeller assembly having an impeller, casing, and a motor according to an illustrated embodiment. 
       
    
    
       [0021]    The following reference characters are used in the specification and figures: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 10 
                 Impeller 
               
               
                   
                 11 
                 Front side 
               
               
                   
                 12 
                 Shroud 
               
               
                   
                 13 
                 Backside 
               
               
                   
                 14a, b 
                 Vane(s) 
               
               
                   
                 16 
                 Hub 
               
               
                   
                 17 
                 Orifice 
               
               
                   
                 18 
                 Impeller axis 
               
               
                   
                 19 
                 Hub protrusion 
               
               
                   
                 20 
                 High pressure surface 
               
               
                   
                 22 
                 Low pressure surface 
               
               
                   
                 24 
                 Upper vane surface 
               
               
                   
                 26 
                 Leading edge 
               
               
                   
                 28 
                 Trailing edge 
               
               
                   
                 30 
                 Lower leading edge 
               
               
                   
                 31 
                 Lower trailing edge 
               
               
                   
                 32 
                 Lower vane body 
               
               
                   
                 33 
                 Central axis 
               
               
                   
                 34 
                 Lower leading surface 
               
               
                   
                 35 
                 Vane edge 
               
               
                   
                 36 
                 Lower trailing surface 
               
               
                   
                 37 
                 Casing 
               
               
                   
                 38 
                 Inlet orifice 
               
               
                   
                 40 
                 Sidewall 
               
               
                   
                 42 
                 Front wall 
               
               
                   
                 43 
                 Inlet port 
               
               
                   
                 44 
                 Cavity 
               
               
                   
                 45 
                 External thread 
               
               
                   
                 46 
                 Discharge port 
               
               
                   
                 48 
                 Outlet orifice 
               
               
                   
                   
               
             
          
         
       
     
       DETAILED DESCRIPTION OF THE INVENTION 
       [0022]      FIGS. 1-5  illustrate an embodiment of an impeller  10  according to the present disclosure. In the illustrated embodiment, the impeller  10  is a radial impeller that includes a shroud  12 , at least two vanes  14   a ,  14   b , and a generally central hub  16 . According to certain embodiments, vanes  14   a ,  14   b  and the shroud  12  may be part of a single, integral construction. The hub  16  may extend from a front side  11  of the shroud  12  and be positioned along an impeller axis  18 . Further, the hub  16  may have a variety of different configurations, including, for example, being generally cylindrical. Additionally, according to certain embodiments, the shroud  12  and/or hub  16  may be configured to be operably connected to a drive shaft, such as, for example, to an impeller shaft that is used to rotate the impeller  10  about the impeller axis  18 . For example, the impeller shaft may be used to rotate the impeller  10  in a circumferential rotation direction R o , as indicated in  FIG. 2 . 
         [0023]    Referencing at least  FIGS. 4 and 5 , the impeller  10  may include an orifice  17  that is configured for connecting the impeller  10  the impeller shaft. For example, according to certain embodiments, the orifice  17  may include an internal thread that is configured for a threaded connection with an external thread of the impeller shaft or a coupling used to connect the impeller  10  to the impeller shaft. Alternatively, the orifice  17  may be sized to receive a portion of the impeller shaft and may include one or more slots that are configured for a keyed connection between the impeller  10  and the impeller shaft. 
         [0024]    Further, according to certain embodiments, the orifice  17  may pass through a hub protrusion  19  that extends outwardly from a backside  13  of shroud  12 , the backside  13  being on a side of the shroud  12  that is opposite of the front side  11  (i.e., the side containing vanes  14   a ,  14   b ). According to certain embodiments, the hub protrusion  19  may be sized to space at least a portion of the shroud  12  from an adjacent wall of a casing. Further, according to certain embodiments, the hub protrusion  19  may be sized to receive a set screw that is used to at least assist in securing the impeller  10  to the impeller shaft. For example, the hub protrusion can be about 0.01″ to about 0.1″, such as about 0.03″. 
         [0025]    In the illustrated embodiment, the impeller  10  has two vanes  14   a ,  14   b  that extend radially outwardly from the hub  16 . Moreover, the two vanes  14   a ,  14   b  extend from two locations that are spaced equidistantly around the circumference of the hub  16 . While other embodiments of the impeller  10  may utilize more than two vanes  14   a ,  14   b , a two vane  14   a ,  14   b  configuration may enhance the overall hydraulic balance of the impeller  10 . 
         [0026]    Each vane  14   a ,  14   b  defines a high pressure surface  20  and a low pressure surface  22 . As best shown by  FIGS. 2 ,  3 B, and  7 , when positioned within a casing  37 , the low pressure surface  22  faces partially outwardly along the impeller axis  18  toward an inlet orifice  38  of the casing  37 . Conversely, the high pressure surface  20  faces partially along the impeller axis  18  away from the inlet orifice  38 . Further, each vane  14   a ,  14   b  has an upper vane surface  24  that lies in a plane that is generally perpendicular to the impeller axis  18 . The upper vane surface  24  meets the high pressure surface  20  along a leading edge  26 . Additionally, the upper vane surface  24  meets the low pressure surface  22  along a trailing edge  28 . 
         [0027]    According to certain embodiments, each vane  14   a ,  14   b  extends along the hub  16  to a lower vane body  32 . According to the illustrated embodiment, the lower vane body  32  may extend along the front side  11  of the shroud  12 . Further, the lower vane body  32  may extend along the front side  11  of the shroud  12  about a central axis  33  that generally lies in a plane that is perpendicular to the impeller axis  18 . The lower vane body  32  may also include a lower leading surface  34  and a lower trailing surface  36 . The lower leading surface  34  may generally meet the high pressure surface  20  at a lower leading edge  30 . The lower trailing surface  36  may generally meet the low pressure surface  22  at a lower trailing edge  31 . 
         [0028]    Each vane  14   a ,  14   b  extends along the hub  16  from the upper vane surface  24  to the lower vane body  32  and sweeps an arc around the hub  16  in a circumferential direction from the leading edge  26  toward the trailing edge  28  that is opposite the circumferential rotation direction R o . The vane  14   a ,  14   b  may sweep an arc around the impeller axis  18  so that the cord length for the leading edge  26  of the upper vane surface  24  to the lower trailing edge  31  achieves a solidity ratio to the vane spacing or pitch of at least 0.46:1. 
         [0029]      FIG. 6  illustrates a cross sectional side view of a casing  37  according to an illustrated embodiment of the present disclosure. The casing  37  includes a sidewall  40  and a front wall  42  that generally define a cavity  44  of the casing  37 . The sidewall  40  and front wall  42  may include a variety of recesses, protrusions, and/or shoulders. For example, as shown in  FIGS. 6 and 7 , the front wall  42  may include an inlet port  43  having an inlet orifice  38  that is in fluid communication with the cavity  44 . Similarly, the sidewall  40  may include a discharge port  46  having an outlet orifice  48  that is in fluid communication with the cavity  44 . The inlet port  43  may be configured for an operable connection to a supply line that is used in the delivery of fluid and/or solids to the inlet orifice  38 . Similarly, the discharge port  46  may be configured for an operable connection with a discharge line that receives fluids and/or solid that is exiting the casing  37 . For example, according to certain embodiments, the inlet and discharge ports  43 ,  46  may be configured for mechanical connection with the supply or discharge lines, respectively, such as a clamped, threaded, or compression engagement, among other connections. In the illustrated embodiment, the inlet and discharge ports  43 ,  46  each include an external thread  45  that is configured for an operable connection with the associated supply or discharge line or associated couplings or connector(s). However, the inlet and discharge ports  43 ,  46  may be configured for a variety of other connections with the associated supply or discharge lines, including, for example, welded or soldered connections, among others. 
         [0030]    Referencing  FIG. 3B , according to certain embodiments, the height (“H”) of the impeller  10  between the upper vane surface  24  and the front side  11  of the shroud  12  is generally equal to the diameter of the outlet orifice  48  of the discharge port  46 . The arc swept by the vane  14   a ,  14   b  (from upper vane surface  24  along the impeller axis to the lower vane body  32 ) extends the high pressure surface  20  extends the acceleration distance and thereby decreases the shear forces applied to fluid moved by the impeller  10  to diminish damage that such forces may cause. The sweep of the vane  14   a ,  14   b  and ratio of the swept arc to impeller height provides relatively gentle re-direction of the liquid and/or solids in the cavity  44  of the casing  37 , thereby reducing abrupt changes in direction for the liquid and/or solids being moved within the cavity  44  and increases overall pump efficiency. 
         [0031]    As shown by at least the leading edge  26  and trailing edge  28  as illustrated in  FIG. 2 , each vane  14   a ,  14   b  may be formed so that the distance between the high pressure surface  20  and the low pressure surface  22  increases as the distance away from the hub  16  increases to a distance R. By increasing the distance between the leading and trailing edges  26 ,  28  as the distance away from the hub  16  increases, the length of a slip path along the high pressure surface  20  in a direction from the hub  16  toward the vane edge  35  may also be increased. The longer slip path may decrease the amount of fluid and/or solids that can travel over the high pressure surface  20  to and around the vane edge  35  to the low pressure surface  22 , thereby reducing recirculation of fluid and/or solids around the impeller  10  and increasing pumping efficiency. 
         [0032]    Reducing recirculation around the vane edge  35  reduces the chances of damaging any fluid and solids entrained in the fluid. The wide slip path on vane surfaces  22  and  24  makes the transit of the liquid from the high pressure side of the impeller to the low pressure side difficult. A tight mechanical tolerance between the pump casing and the upper vane surface  42  makes this design highly efficient as it reduces the liquids ability to recirculate inside the pump. In addition to the wide area of the slip path, the integral rear shroud limits recirculation from the high pressure to low pressure thus eliminating the liquids ability to recirculate at the back of the impeller, further improving the efficiency of the pump. 
         [0033]    As shown in at least  FIG. 7 , when positioned in the casing  37 , the shroud  12  is positioned axially behind the vanes  14   a ,  14   b . Further, the shroud  12  has generally the same or similar outer diameter as the impeller  10 . More specifically, the shroud  12  has a radius from the impeller axis  18  that is similar to the distance from the impeller axis  18  to the vane edge  35 . The thickness of the integral shroud, as a ratio of the impeller height, is determined to be about 0.337. The shroud serves to offset the impeller axially away from the back of the casing and, more particularly, forward from the casing discharge port. 
         [0034]    The front of the casing consists of two concentric radii from the central axis. The major diameter D 1  is axially rearward and of sufficient size beyond the impeller diameter to facilitate efficient transfer from kinetic to potential energy, as understood in the art. The height of the major diameter is equal to the diameter of the outlet port. The minor diameter D 2  is axially forward and is the same diameter as the impeller plus that which is necessary for mechanical clearance (e.g., the minimum clearance between a vane edge of the impeller and the casing at the minor diameter is about 0.02″). The height of the minor diameter is equivalent to that of the impeller shroud. The transition from minor to major casing diameter is stepped such that there is a 90° angle from the major diameter to a transition step that is perpendicular to the axis and a 90° angle from the transition step to the minor diameter. This stepped casing provides a narrowing fluid channel from the axial front to the axial rear as the fluid translates from the impeller hub to the impeller periphery. This channel provides a smooth and efficient path while limiting recirculation and therefore improving pump efficiency, both of which result in lower fluid and solids damage. 
         [0035]    The impeller described in this disclosure provides a centrifugal impeller and casing which can pump shear sensitive and high solids liquids with high efficiencies and low product damage. The helical vane sweep induces laminar flow. The impeller vanes, shroud, and casing reduce recirculation and assist inducement of laminar flow, therefore requiring less power. 
         [0036]    One metric used in the dairy industry to measure the quality of milk is the acid degree value (“ADV”). The ADV measures the presence of long chain fatty acids in the milk. There is a correlation between the ADV and the flavor of milk because rancidity results from the release of free fatty acids in the milk. When used in dairy processing applications, conventional pumps typically produce an undesirable increase in the ADV of the milk as a result of fat globule damage due to mechanical shearing. This increase in the ADV can negatively affect the taste of the milk. In contrast, when a pump employing the claimed impeller and casing is used to pump milk, there is either no significant change in the ADV level as a result of pumping or even a decrease in the ADV level. This advantageous result reflects that pumps employing the claimed impeller and casing cause less product damage due to mechanical shearing than conventional systems. 
         [0037]    This beneficial result was confirmed by two independent tests, the results of which are summarized in the working examples and Tables 1 and 2 below. 
       Example 1 
     Tests Performed by Silliker, Inc 
       [0038]    The ADV levels of various milk samples were measured before pumping and after pumping using a pump employing the claimed impeller and casing—namely, the Bowpeller model B3258 8″ centrifugal pump—in Trials A and B and a competitor&#39;s conventional 8″ centrifugal pump in Trials C and D. The results, summarized in Table 1, show that in Trials C and D, the ADV of the milk consistently increased as a result of pumping using the competitor&#39;s conventional pump, thereby indicating undesirable mechanical agitation and foaming of the milk due to pumping. However, Trials A and B show that the ADV of the milk consistently decreased (or at least did not change) as a result of pumping using the claimed impeller and casing—a highly desirable outcome. 
       Example 2 
     Tests Performed by Eurofins DQCI LLC 
       [0039]    The ADV levels of various milk samples were measured before pumping and after pumping using a pump employing the claimed impeller and casing—namely, the Bowpeller model B15154 4″ centrifugal pump—in Trials E and F and a competitor&#39;s conventional 4″ centrifugal pump in Trials G and H. The results, summarized in Table 2, show that in Trials G and H, the ADV of the milk consistently increased as a result of pumping using the competitor&#39;s conventional pump, thereby indicating undesirable mechanical agitation and foaming of the milk due to pumping. However, Trials E and F show that the ADV of the milk consistently decreased (or at least did not change) as a result of pumping using the claimed impeller and casing—a highly desirable outcome. 
         [0040]    This data confirms that a pump employing the claimed impeller and casing is capable of pumping shear sensitive liquids (such as milk) without applying damaging forces to the liquid. This result would also have beneficial application in food processing systems, pharmaceutical processing systems, and clay slurries. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Tests Performed by Silliker, Inc. 
               
             
          
           
               
                   
                 Acid Degree  
                 Acid Degree  
                 Change in  
               
               
                   
                 Value  
                 Value 
                 Acid Degree  
               
               
                   
                 (Dairy Tank; 
                 (Truck Tanker; 
                 Value Due 
               
               
                 Pump 
                 Before Pumping) 
                 After Pumping) 
                 to Pumping 
               
               
                   
               
             
          
           
               
                 Applicant Trial A 
                 0.98 
                 0.97 
                 −0.01 
               
               
                 Applicant Trial B 
                 0.99 
                 0.95 
                 −0.04 
               
               
                 Competitor Trial C 
                 0.90 
                 0.94 
                 +300.04 
               
               
                 Competitor Trial D 
                 0.86 
                 0.94 
                 +300.08 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Tests Performed by Eurofins DQCI LLC 
               
             
          
           
               
                   
                 Acid Degree  
                 Acid Degree  
                 Change in  
               
               
                   
                 Value 
                 Value 
                 Acid Degree  
               
               
                   
                 (Raw Milk; 
                 (Raw Milk; 
                 Value Due  
               
               
                 Pump 
                 Before Pumping) 
                 After Pumping) 
                 to Pumping 
               
               
                   
               
             
          
           
               
                 Applicant Trial E 
                 0.82 
                 0.73 
                 −0.09 
               
               
                 Applicant Trial F 
                 0.82 
                 0.69 
                 −0.13 
               
               
                 Competitor Trial G 
                 0.63 
                 0.68 
                 +0.05 
               
               
                 Competitor Trial H 
                 0.63 
                 0.77 
                 +0.14 
               
               
                   
               
             
          
         
       
     
         [0041]    The present disclosure has been described by reference to certain embodiments, however, it will be understood by those skilled in the art that the described embodiments do not limit the present disclosure and that the disclosure may be practiced other than as by the described embodiments, and encompasses all sizes, configurations, alternatives, modifications, and equivalents within the scope of the appended claims.