Abstract:
The disclosure provides pumps that include improvements in construction, which involve bearing surfaces, recirculation paths, mounting footprints, impeller vane starting diameters, canister assemblies, and rotor assembly bushing configurations.

Description:
BACKGROUND 
       [0001]    Field of the Invention 
         [0002]    The present invention generally relates to pumps, which could be in various configurations, such as in the form of rotodynamic or centrifugal pumps, or positive-displacement pumps, and which may be magnetically driven or may have dynamic seals. 
         [0003]    Description of the Related Art 
         [0004]    Many pumps utilize dynamic seals, which are mechanical seals between rotating parts. However, in some pumping applications, it is desirable to try to avoid potential seal leakage by not using seals in conjunction with rotating parts. Accordingly, in some instances, it is becoming more common in the pump arts to employ a magnetic drive system to eliminate the need for seals along rotating surfaces. The present disclosure addresses numerous shortcomings in prior art equipment, such as pumps, some of which utilize a magnetic coupling, while others of which may be employed with pumps having seals along rotating surfaces. The pumps also may employ rotodynamic or positive-displacement pumping principles. The following are several of the shortcomings recognized and sought to be addressed in the present disclosure. 
         [0005]    Prior art systems for supporting a rotor assembly within a magnetically driven pump may be of different constructions but tend to provide radial and axial (thrust) bearing support for the rotor assembly that does not rely on the canister that separates the fluid pumping chamber from the drive portion of the pump. This results in a disadvantage of causing magnetically driven pumps to have greater axial length and weight, because the bearing support is located forward and/or rearward of the pumping portion of the rotor assembly. For example, bearings providing radial support and forward and rearward thrust or axial bearings that restrict forward or rearward motion typically are located forward and/or rearward of the pumping elements of a rotor assembly. 
         [0006]    Almost all magnetically coupled pumps have a recirculation path that allows a small percentage of the pump fluid flow to recirculate from the pump outlet or discharge side, back to the inlet or suction side. This recirculation is used mostly for lubrication and cooling of bushings and for cooling of the canister, which may get hot due to electrical eddy currents generated by the magnetic coupling. Prior art recirculation paths include one or more segments where the path is essentially a hole thru a single part, such as a hole thru a single stationary part of the pump casing or thru a single piece rotating impeller. The downside of a hole thru a single part is that it is prone to causing clogging of the recirculation path. 
         [0007]    In the chemical processing industry, the standard ASME B73.1 is a very popular specification for most centrifugal dynamically sealed pumps. In this standard and in the ISO 5199 standard, one of the main features of the specification is the establishment of a common mounting footprint, including the sizes and locations of the outlet or discharge port, the inlet port, the mounting foot and the shaft of the pump. The industry also sells magnetically coupled pumps but they utilize a different rear end mechanical drive portion or power end in comparison to the dynamically sealed pumps. There are far fewer magnetically coupled pumps, so the power ends for magnetically driven pumps tend to be more costly. Also, due to overall size and especially axial length, no magnetically coupled pumps known to the inventors have been able to utilize the power end that is commonly used with the dynamically sealed pumps while meeting either of the standards for the location of the stated features involved in mounting such pumps. 
         [0008]    When a rotor assembly of a pump includes an impeller, the pump generally is most efficient and has the best suction capability when the center starting ends of the vanes have a relatively small diameter. However, in a magnetically driven rotodynamic pump, a front nose cap that holds a front axial bearing is most beneficial if it has a relatively large outer diameter, so that the axial bearing can be large. In a typical design, a nose cap must be assembled from the front of the impeller, so the center of the forward ends of the impeller vanes must start at a diameter at least as large as the diameter of the nose cap. This requires a disadvantageous tradeoff pitting a desired small diameter for the front end of the impeller vanes against a desired large diameter of a front axial bearing. 
         [0009]    As noted above, it is common for pumps to have separate radial and axial bushings or bearings. This tends to add undesirable complexity and length to a pump. 
         [0010]    The above are some of the shortcomings of prior art pumps that are sought to be addressed by the teachings and examples provided in the present disclosure. 
       SUMMARY 
       [0011]    In a first aspect, the present disclosure provides a magnetically driven pump having a compact advantageous design that overcomes the above discussed disadvantages associated with having radial and axial bearing surfaces well forward or rearward of the pumping area of a rotor assembly. The disclosure provides a magnetically driven pump that includes a casing, a rotor assembly, an inner magnet assembly and a canister assembly. The casing has a front portion, a rear portion, a discharge port and an inlet port. The rotor assembly includes a rear cylindrical opening having an inner wall surface and having a plurality of magnet segments connected to the inner wall surface, a front cylindrical opening having an inner wall surface that provides a radial bearing surface, and a first axial bearing surface. The canister assembly includes a cylindrical portion disposed within a radial gap between magnet segments of the inner magnet assembly and magnet segments of the rotor assembly, and a front portion extending from the cylindrical portion and having a radial bearing surface and a first axial bearing surface. In this design, the radial bearing surface of the rotor assembly and the radial bearing surface of the canister assembly front portion restrict radial motion of the rotor assembly, and the first axial bearing surface of the rotor assembly and the first axial bearing surface of the canister assembly front portion restrict forward motion of the rotor assembly. 
         [0012]    In a second aspect, the present disclosure addresses the disadvantageous structures of prior art magnetically driven pumps having a recirculation path through a single part or through stationary segment. The disclosure provides a magnetically driven pump that includes a stationary casing, a rotatable rotor assembly, a rotatable drive magnet assembly, a stationary canister assembly, and a recirculation path. The stationary casing has a front portion, a rear portion, a discharge port and an inlet port. The rotatable rotor assembly includes a rotor, at least one radial bearing surface, at least one axial bearing surface and a plurality of magnet segments. The rotatable drive magnet assembly includes a plurality of magnet segments in axial alignment with the magnet segments of the rotor assembly. The stationary canister assembly includes a cylindrical portion disposed within a radial gap between the magnet segments of the rotor assembly and the magnet segments of the drive magnet assembly. The recirculation path extends from the casing discharge port, across the at least one radial bearing surface of the rotor assembly, across the at least one axial bearing surface of the rotor assembly, across the cylindrical portion of the canister assembly, and to the casing inlet port, wherein when the rotor assembly rotates within the casing and relative to the canister assembly, all portions of the recirculation path include at least one stationary surface of the casing or canister assembly that is opposed to at least one surface of the rotor assembly. 
         [0013]    In a third aspect, the present disclosure also addresses the lack of magnetically driven pumps able to meet the industry standards ASME B73.1 and/or ISO 5199 for mounting locations of key features and able to utilize the rear end mechanical drive portion commonly used with dynamically sealed pumps that meet the standard. The disclosure provides a magnetically driven rotodynamic pump that includes a stationary casing, an inner magnet assembly, and an impeller assembly. The stationary casing includes a discharge port, an inlet port, a mounting foot and a rear mounting flange. The inner magnet assembly has an inner ring and a plurality of magnet segment. The casing, inner magnet assembly and impeller assembly are configured and dimensioned to be assembled to a power end and adapter of a commercially available non-magnetically driven rotodynamic pump having a dynamic seal that is designed in accordance with dimensions specified in a pump industry standard, such that when assembled, the sizes and locations of the casing discharge port, the casing inlet port, the casing mounting foot, and the power end and adapter all meet the dimensions specified in the standard. The unique, axially compact design of a pump of the present disclosure is capable of utilizing the rear end mechanical drive components or power end normally in place for such centrifugal dynamically sealed pumps. Thus, the pump may be installed without needing to remove the power end that is connected to the electric drive motor, and therefore, without disturbing the electric motor and its mounting and electrical connections, and without disturbing the shaft alignment between the electric motor and the power end. Also, the new pump advantageously may be connected to existing power end and adaptor structures. This can be particularly beneficial to manufacturers that already make the power end and adapter components for the centrifugal dynamically sealed pumps. Moreover, it permits utilization of the less expensive power ends normally used with dynamically sealed pumps, and provides an opportunity for field retrofits that can be achieved by leaving in place the existing power end and only changing out the pump, while also gaining the advantages of a magnetically driven pump. 
         [0014]    In a fourth aspect, the present disclosure addresses the previously noted issue that typical magnetically driven rotodynamic pumps having a front axial bearing at a nose cap must balance the benefit of having a small diameter at the center starting portion of the impeller vanes against the benefit of having a large diameter canister nose cap for the front axial bearing. The disclosure provides a magnetically driven rotodynamic pump having a stationary casing, a stationary canister assembly, and a rotatable rotor assembly. The stationary casing has a front portion, a rear portion, a discharge port and an inlet port. The stationary canister assembly is connected to the stationary casing. The stationary canister assembly further includes a canister and a stationary nose cap is connected to the canister and has an outer diameter, a rear axial bearing surface and a front surface. The rotatable rotor assembly includes an impeller having a plurality of front vanes, wherein a portion of the impeller front vanes extend forward of the nose cap front surface and inward to an inner diameter that is smaller than the outer diameter of the nose cap. Thus, the design includes the benefits of both a smaller diameter at the center starting portion of the impeller vanes and a large diameter canister nose cap having a front axial bearing. In this design, the stationary front surface of the nose cap is positioned where there would otherwise be an impeller base surface and the forward extending portions of the impeller vanes extend forward of the surface of the base of the impeller. This results in an advantageous relatively small diameter of the center starting ends of the impeller vanes combined with an advantageous relatively large outer diameter of the axial bearing at the nose cap of the canister assembly. 
         [0015]    In a fifth aspect, the present disclosure provides a pump that includes a stationary casing having a front portion, a rear portion, a discharge port and an inlet port, and further includes a rotor assembly having a bushing wherein the bushing is of single piece construction and includes a radial bearing surface that restricts radial motion of the rotor assembly, a front axial bearing surface that restricts forward motion of the rotor assembly, and a rear axial bearing surface that restricts rearward motion of the rotor assembly. This design is believed to provide the first instance of a pump having a bushing for a rotor assembly that is of single piece construction while providing radial and front and rear axial bearing surfaces. This provides a particularly compact rotor assembly design. 
         [0016]    In an sixth aspect, the present disclosure provides a pump that includes a stationary casing having a front portion, a rear portion, a discharge port and an inlet port, and further includes a rotor assembly having a rotor that includes a central opening extending axially through the rotor and having a step proximate one end of the central opening, a rotor ring, and a bushing, wherein the bushing fits inside the rotor central opening and is held in place between the rotor ring and the step in the central opening of the rotor. This design provides a uniquely compact and efficient bushing design and construction for a rotor assembly wherein a bushing extends through a portion of and is held within the rotor assembly by a fastening means at one end of the rotor assembly. This also enables the use of advantageous longer bearing surfaces. 
         [0017]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and provided for purposes of explanation only, and are not restrictive of the subject matter claimed. Further features and objects of the present disclosure will become more fully apparent in the following description of the preferred embodiments and from the appended claims. Indeed, it is contemplated that certain aspects of the present disclosure pertain to pumps that may be dynamically sealed and/or magnetically driven and considered to be sealless, while certain aspects also pertain to rotodynamic pumps and/or positive-displacement pumps. It also will be appreciated that, if magnetically driven, some aspects may be applied to pumps having an inner magnet drive assembly and/or an outer magnet drive assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    In describing the preferred embodiments, references are made to the accompanying drawing figures wherein like parts have like reference numerals, and wherein: 
           [0019]      FIG. 1  provides a side view and a front view of a first example pump connected to a motor using an adapter and shaft extension in a close-coupled fashion. 
           [0020]      FIG. 2  provides a quarter-sectioned perspective view of the first example pump of  FIG. 1 . 
           [0021]      FIG. 3  provides an enlarged closer perspective view of the quarter-sectioned area of  FIG. 2 . 
           [0022]      FIG. 4  provides a perspective view of the first example pump of  FIG. 1  with a sectioned front portion of the casing. 
           [0023]      FIG. 5  provides a front view of the first example pump of  FIG. 1  with a sectioned front portion of the casing. 
           [0024]      FIGS. 6 a  and 6 b    provide quarter-sectioned rear and front perspective views of the rotor assembly of the first example pump of  FIG. 1 . 
           [0025]      FIG. 7  provides a quarter-sectioned perspective partially exploded view of the inner portion of the first example pump of  FIG. 1 . 
           [0026]      FIG. 8  provides a partially quarter-sectioned perspective partially exploded view of the rotor assembly of the first example pump of  FIG. 1 . 
           [0027]      FIG. 9  provides a perspective exploded view of the center portion of the first example pump of  FIG. 1 . 
           [0028]      FIG. 10  provides a portion of a quarter-sectioned plan view of the first example pump of  FIG. 1  showing a recirculation path and without the power end drive components. 
           [0029]      FIG. 11  provides a side view and a front view of a second example pump connected to a power end that is suitable for another pump meeting ASME B73.1 or ISO 5199 dimensional standards. 
           [0030]      FIG. 12  provides a quarter-sectioned perspective view of the second example pump of  FIG. 11 . 
           [0031]      FIG. 13  provides a quarter-sectioned perspective partially exploded view of the second example pump of  FIG. 11 . 
           [0032]      FIG. 14  provides a front perspective view of a third example pump. 
           [0033]      FIG. 15  provides a cross-sectioned view of the third example pump of  FIG. 14 . 
           [0034]      FIG. 16  provides a front perspective partially exploded view of the third example pump of  FIG. 14 . 
           [0035]      FIG. 17  provides a rear perspective partially exploded view of the third example pump of  FIG. 14 . 
           [0036]      FIG. 18  provides a front perspective exploded view of the rotor assembly of the third example pump of  FIG. 14 . 
           [0037]      FIG. 19  provides a front perspective exploded view of the drive magnet assembly of the third example pump of  FIG. 14 . 
           [0038]      FIG. 20  provides a quarter-sectioned perspective partially exploded view of the drive magnet assembly, canister and rotor assembly of the third example pump of  FIG. 14 . 
           [0039]      FIG. 21  provides a portion of a quarter-sectioned plan view of the pump of  FIG. 14  showing a recirculation path and without the power end drive components. 
       
    
    
       [0040]    It should be understood that the drawings are not to scale. While some mechanical details of the example pumps, including details of fastening means and other plan and section views of the particular components, have not been shown, such details are considered to be within the comprehension of those skilled in the art in light of the present disclosure. It also should be understood that the present disclosure and claims are not limited to the preferred embodiments illustrated. 
       DETAILED DESCRIPTION 
       [0041]    Referring generally to  FIGS. 1-21 , it will be appreciated that pumps devices of the present disclosure generally may be embodied within numerous configurations. Indeed, the teachings within this disclosure may pertain to dynamically sealed pumps, whether of the rotodynamic or positive-displacement types, and/or to magnetically driven or sealless pumps, whether of the rotodynamic or positive-displacement types. If of the magnetically driven type, the pumps may be of the inner magnet drive and/or outer magnet drive types. 
         [0042]    Referring to a preferred first example embodiment, in  FIGS. 1-10 , and particularly to  FIGS. 1 and 2 , an example pump  2  is shown connected to a motor adapter  4  that, in turn, is connected to a standard C-face electric motor  6 . The configuration of pump  2  happens to be a magnetically driven rotodynamic pump. More particularly, a first flange  5  of the adapter  4  is connected to the motor  6  by use of a plurality of fasteners  8 , such as threaded screws or other suitable means of connection. In this first example, the motor  6  includes a motor shaft  22  to which is connected a shaft extension  620 , and it will be appreciated that in combination with the adapter  4 , these components provide the rear end mechanical drive portion or power end that is connected to the pump  2 . 
         [0043]    The pump  2  includes a casing  100  that is intended to be mounted in place, so as to be stationary. The casing  100  includes a front portion  100   a  and a rear portion  100   b . The casing  100  also has an outlet or discharge port  102  and an inlet port  104 . In this first example, the discharge port  102  is radially facing, while the inlet port  104  is axially facing, although alternative configurations may be utilized. The casing  100  includes a rear face  106  that is connected to a second flange  7  of the adapter  4  by use of a plurality of fasteners  10  that pass through apertures in the second flange  7  and engage threaded holes in the casing rear face  106 . The casing  100  may be constructed of rigid materials, such as steel, stainless steel, cast iron or other metallic materials, or structural plastics or the like. 
         [0044]    As may be seen in  FIGS. 2 and 9 , the pump  2  also includes a backplate  200  that has an outer flange  202 . The backplate outer flange  202  is clamped between the casing  100  and the adapter  4  when connecting the pump  2  to the adapter  4  by installing the fasteners  10 . Sealing is provided between the casing  100  and the backplate  200  by an O-ring  13 , although other methods of sealing may be employed, such as use of a gasket, liquid sealant or the like. The pump  2  also includes a rear cover  300  that has an outer flange  302 . The rear cover  300  is connected to the backplate  200  by use of a plurality of fasteners  14 , such as threaded screws that pass through apertures  304  in the rear cover  300  and engage threaded holes in a rear face of the backplate  200 . 
         [0045]    The pump  2  also includes a canister assembly  400  that includes a canister  400   a  that has an outer flange  402 . The canister outer flange  402  is clamped between the backplate  200  and the rear cover  300  when connecting the rear cover  300  to the backplate  200  by installing the fasteners  14 . Sealing is provided between backplate  200  and the canister assembly  400  by an O-ring  16 , although other methods of sealing may be employed, such as use of a gasket, liquid sealant or the like. The canister assembly  400  also includes a front portion  404  that includes a front face  406  having a front cavity  408  and an aperture  410  that passes through the front portion  404 . The canister assembly  400  may be constructed of rigid materials. It will be appreciated that common materials may be used, such as stainless steel, or low conductivity metals, such as alloy C-22 or alloy C-276, and it could be advantageous to use materials having very low electrical conductivity, such as silicon carbide, ceramic, polymers or the like. 
         [0046]    In addition, the canister assembly  400  includes a nose cap  500 , which has a threaded hole  502 , a rear face  504  and a rear extended portion  506 . The nose cap  500  is attached to the canister assembly front portion  404  by a fastener  18 , such as a threaded screw that passes through the aperture  410  in the front portion  404  and engages the threaded hole  502  in the rear of the nose cap  500 . In this first example embodiment, there is just one fastener  18  securing the nose cap  500 , but it will be appreciated by one of skill in the art that a plurality of fasteners or other suitable fastening means may be employed in assembling the components of the canister assembly  400 . Also, in this first example pump  2 , the front portion  404  and nose cap  500  of the canister assembly  400  are spaced from the front portion  100   a  of the casing  100 , such that they do not receive support from the front portion  100   a . The nose cap  500  may be constructed of rigid materials, such as steel, stainless steel, cast iron or other metallic materials, or structural plastics or the like. 
         [0047]    The shape of the front cavity  408  is not cylindrical, and it corresponds to a non-cylindrical shape of the nose cap extended portion  506 , so as to prevent relative rotation between the nose cap  500  and canister  400   a  when connected by the fastener  18 , and to ensure that the canister assembly will remain stationary. Throughout this disclosure, it will be appreciated that alternative ways of preventing relative rotation between components may be used, such as by use of one or more fasteners, welding or other suitable alternatives. Sealing between the canister  400   a  and the nose cap  500  is provided by an O-ring  20 , although other methods of sealing may be employed, such as use of a gasket, liquid sealant or the like. 
         [0048]    The pump  2  further includes a drive magnet assembly, such as an inner magnet assembly  600  that includes an inner ring  640  which may be connected directly to a motor shaft, or in this example, to the shaft extension  620 . The inner ring  640  has a central threaded aperture  642  and the shaft extension  620  has a mating externally threaded front portion  622 , which is used to connect the inner ring  640  to the shaft extension  620 . In this first example embodiment, the shaft extension  620  and inner ring  640  are separate pieces, but it will be appreciated that they could be combined, so as to be a single piece, or a different method of connection may be used. The inner ring  640  may be constructed of rigid materials, but is preferably constructed of a material with high magnetic permeability, such as iron, carbon steel or the like. 
         [0049]    The shaft extension  620  of this example includes an inner opening  624  that slidably receives a shaft  22  of the motor  6 . The shaft extension  620  also includes a keyway  626  and one or more threaded apertures  628 . A key  24  is positioned in the shaft extension keyway  626  and engages with a keyway  26  of the motor shaft  22 , to provide a positive rotational connection between the shaft extension  620  and the motor shaft  22 . One or more setscrews  28  are positioned in the shaft extension threaded apertures  628  and are tightened against the keyway  26  of the motor shaft  22 , to provide a positive axial connection between the shaft extension  620  and the motor shaft  22 . 
         [0050]    The inner ring  640  of the drive magnet assembly, such as inner magnet assembly  600  includes an outer surface  644  to which are connected twenty-four magnet segments  646 , although it will be appreciated that one may have an embodiment with a different quantity of magnet segments. The magnet segments  646  are radially charged and are positioned with alternating polarity. The magnet segments  646  are rigidly connected to the inner ring  640  using an adhesive, although alternative suitable means of connection may be used, such as use of fasteners or the like. Although not required, this example embodiment includes an inner magnet sleeve  648  having a thin cylindrical portion  650  that closely fits over the outer surfaces of the magnet segments  646 . 
         [0051]    The pump  2  also includes a rotatable rotor assembly, such as a rotatable impeller assembly  700  that includes a rotor, such as an impeller  702 . The impeller  702  includes a rear opening  704 , which receives a driven magnet assembly, such as an outer magnet assembly  705 . The outer magnet assembly  705  includes an outer ring  706  having an inner wall surface  708  to which are connected twenty-four magnet segments  710 , which corresponds to the number connected to the inner ring  640 , although it will be appreciated that one may have an embodiment with a greater or lesser quantity of magnet segments. The magnet segments  710  are radially charged and are positioned with alternating polarity. The magnet segments  710  are rigidly connected to the outer ring  706  using an adhesive, although alternative suitable means of connection may be used, such as use of fasteners or the like. An impeller magnet sleeve  712  is included having a thin cylindrical portion  714  that closely fits along the inner surfaces of the magnet segments  710 . The impeller magnet sleeve  712  also includes a rear flange  718 . The impeller magnet sleeve  712  is sealingly connected to the impeller  702  by continuous weld joints located at an outer end  720  of the rear flange  718  and at a front end  722  of the cylindrical portion  714 . It will be appreciated by one of skill in the art that other methods of connection may be used, such as liquid adhesive, gaskets, O-rings or the like. The rotor or impeller  702  may be constructed of rigid materials, such as steel, stainless steel, cast iron or other metallic materials, or structural plastics or the like. The outer ring  706  may be constructed of rigid materials, but preferably is constructed of a material with high magnetic permeability, such as iron, carbon steel or the like. 
         [0052]    Referring to  FIGS. 6 a  and 6 b   , the rotatable rotor assembly or impeller assembly  700  includes a rotor or impeller  702  having a central opening  724  that includes one or more grooves  726 . A bushing  800  is received in the central opening  724  of the rotor or impeller  702 , and one or more O-rings  30  are positioned between an outer surface  802  of the bushing  800  and the grooves  726  in the central opening  724  of the impeller  702 . The bushing  800  is held in a forward direction against a step  727  in the central opening  724  proximate an end of the central opening  724  of the impeller  702 , where there is a transition from a first inner surface  727   a  to a second inner surface  727   b  having a smaller diameter. The bushing outer surface  802  is slightly smaller than the rotor or impeller central opening  724 , and the O-rings  30  are not intended to provide sealing between the two surfaces. Rather, in the event that the operating temperature may vary, and the bushing  800  and the impeller  702  may be made of materials with different rates of thermal expansion, then the size or extent of the clearance between the bushing  800  and impeller  702  will change and the compression of the O-rings  30  of this example embodiment will accommodate this clearance change and will maintain a concentric relationship between the bushing  800  and the impeller  702 . 
         [0053]    The rotor or impeller  702  further includes a rear surface  728  that includes one or more threaded holes  730 . An impeller rear cap, such as rotor ring  732  having a central opening  736  is connected to the impeller rear surface  728  by at least one fastener  32 , such as by a plurality of screws that pass through apertures  734  in the rotor ring  732  and engage the threaded holes  730  in the impeller  702 . The bushing  800  includes a rear portion  804  with a shape that is not cylindrical, and it corresponds to a non-cylindrical shape of the central opening  736  in the rotor ring  732  to prevent relative rotation between the bushing  800 , rotor ring  732  and impeller  702 , although as previously noted, alternative ways of preventing relative rotation may be utilized. Thus, the bushing  800  fits inside the central opening  736  extending axially through the rotor or impeller  702  and is held in place between the rotor ring  732  and the step  727  in the central opening  736  of the impeller  702 . 
         [0054]    As will be further described and more fully appreciated, within this first example pump  2 , the bushing  800  provides the rotatable rotor assembly or impeller assembly  700  a radial bearing surface, a first or front axial bearing surface, and a second or rear axial bearing surface. In this example, these bearing surfaces engage respective bearing surfaces of the canister assembly  400 , which as will be described further herein more particularly include a radial bearing surface provided by a bearing sleeve  806 , a first or front axial bearing surface provided by a front thrust washer  818 , and a second or rear axial bearing surface provided by a rear thrust washer  814 . 
         [0055]    Thus, the canister assembly  400  of the first example pump  2  also includes a stationary bearing sleeve  806  that has a cylindrical shape. The front portion  404  of the canister  400   a  includes an outer surface  412  having at least one groove  414 . The bearing sleeve  806  is positioned over the outer surface  412  of the front portion  404 , and at least one O-ring  34  is positioned between the outer surface groove  414  of the front portion  404  and an inner surface  808  of the bearing sleeve  806 . In this example embodiment, two O-rings  34  are received in two grooves  414 . The outer surface  412  of the front portion  404  of the canister  400   a  is slightly smaller than the inner surface  808  of the bearing sleeve  806 . In the event that the operating temperature may vary and the canister  400   a  and the bearing sleeve  806  may be made of materials with different rates of thermal expansion, then the size or extent of the clearance between the canister  400   a  and the bearing sleeve  806  will change. The O-rings  34  are not intended to seal, but the compression of the O-rings  34  will accommodate this clearance change and will maintain a concentric relationship between the canister  400   a  and the bearing sleeve  806 . In this manner, the bearing sleeve  806  provides the canister assembly  400  with a radial bearing surface for rotational engagement with the bushing  800  of the rotor assembly  700 . 
         [0056]    The outer surface  810  of the stationary bearing sleeve  806  provides the canister assembly  400  a radial bearing surface at the front portion  404  of the canister  400   a , which is slightly smaller than an inner wall surface  812  of the bushing  800 . The inner wall surface  812  serves as a central cylindrical opening for the rotor assembly, such as impeller assembly  700 , and provides a radial bearing surface for the impeller assembly  700 . Thus, the rotatable rotor assembly, such as impeller assembly  700 , has a bushing  800  having a radial bearing surface  812  that rotates in engagement with and is supported by the outer surface  810  of the stationary bearing sleeve  806  of the canister assembly  400 . 
         [0057]    The canister assembly  400  of pump  2  of this first example embodiment also includes a stationary rear thrust washer  814  having a central opening  816  with a shape that is not cylindrical. The canister  400   a  includes a center portion  416  having a non-cylindrical shape that corresponds to the shape of the central opening  816  of the rear thrust washer  814 , to prevent relative rotation between the canister  400  and rear thrust washer  814 , although suitable alternative ways of preventing relative rotation may be utilized. The canister  400   a  includes a center wall  418  that has a front surface  420 . The rear thrust washer  814  is positioned over the canister center portion  416  and against the front surface  420  of the canister center wall  418 . 
         [0058]    The canister assembly  400  of pump  2  further includes a stationary front thrust washer  818  with a central opening  820  having a shape that is not cylindrical. The nose cap  500  includes a center portion  508  having a non-cylindrical shape that corresponds to the shape of the central opening  820  of the front thrust washer  818  to prevent relative rotation between the nose cap  500  and front thrust washer  818 , although suitable alternative ways of preventing relative rotation between the components of the canister assembly  400  may be utilized. The nose cap  500  has a front surface  509  that includes a front flange  510 . The front flange  510  also has a rear surface  512 . The front thrust washer  818  is positioned over the center portion  508  of the nose cap  500  and against the rear surface  512  of the front flange  510  of the nose cap  500 . 
         [0059]    It will be appreciated that while the bearing sleeve  806  provides the canister assembly  400  a radial bearing surface  810 , the front thrust washer  818  has a rear surface  828  that provides the canister assembly  400  a first or front axial bearing surface and the rear thrust washer  814  has a front surface  826  that provides the canister assembly  400  a second or rear axial bearing surface, these bearing surfaces alternatively could be integral with the front portion  404  of the canister assembly  400 . 
         [0060]    The bushing  800  of the rotor assembly or impeller assembly  700  has a length that is slightly shorter than the length of the bearing sleeve  806  of the canister assembly  400 . The bearing sleeve  806  is positioned between the rear thrust washer  814  and the front thrust washer  818  of the canister assembly  400 , creating a gap equal to the length of the bearing sleeve  806 . The impeller assembly  700  is positioned such that the bushing  800  is in the gap between the rear thrust washer  814  and the front thrust washer  818 . The bushing  800  also has a front surface  822  and a rear surface  824 . The front surface  822  provides the impeller assembly  700  a first or front axial bearing surface. Similarly, the rear surface  824  provides the impeller assembly  700  a second or rear axial bearing surface. Thus, the pump  2  includes a rotatable rotor assembly  700  that includes a bushing  800  wherein the bushing  800  is of single piece construction and includes a radial bearing surface  812  that restricts radial motion of the rotor assembly, a front axial bearing surface  822  that restricts forward motion of the rotor assembly  700 , and a rear axial bearing surface  824  that restricts rearward motion of the rotor assembly  700 . 
         [0061]    Under some pump operating conditions, the impeller assembly  700  may experience a rear thrust force, pushing the impeller assembly  700  rearward and causing the rear surface  824  of the bushing  800  to rotatably engage the front surface  826  of the rear thrust washer  814 . Under other pump operating conditions, the impeller assembly  700  may experience a forward thrust force, pushing the impeller assembly  700  forward and causing the front surface  822  of the bushing  800  to rotatably engage the rear surface  828  of the front thrust washer  818 . The bushing  800  also includes one or more grooves  830  on the front face  822 , rear face  824  and inner surface  812 , which are connected. The radial bearing surface  812  of the rotor assembly  700  and the radial bearing surface  810  of the canister assembly front portion restrict radial motion of the rotor assembly  700 , and the first axial bearing surface  822  of the rotor assembly  700  and the first axial bearing surface  828  of the canister assembly front portion  404  restrict forward motion of the rotor assembly  700 . In addition, the rotor assembly  700  further comprises a second axial bearing surface  824 , the canister assembly front portion further comprises a second axial bearing surface  826 , and the second axial bearing surface of the rotor assembly  824  and the second axial bearing surface  826  of the canister assembly front portion  404  restrict rearward motion of the rotor assembly  700 . 
         [0062]    The canister  400   a  includes a thin cylindrical portion  422  having an inner surface  424  that is slightly larger than the outer surface  652  of the inner magnet assembly  600 , and having an outer surface  426  that is slightly smaller than the inner surface  738  along the thin cylindrical portion  714  of the impeller magnet sleeve  712 . The casing  100 , backplate  200 , and canister assembly  400 , with its canister  400   a  and nose cap  500 , all remain stationary, are sealingly connected, and together form a sealed fluid chamber rearward of the canister assembly  400 . 
         [0063]    The magnet segments  646  of the drive magnet assembly or inner magnet assembly  600  are in axial alignment with the magnet segments  710  of the outer magnet assembly  705  of the rotatable rotor assembly or impeller assembly  700 . The stationary cylindrical portion  422  of the canister assembly  400  is located in a radial gap between the magnet segments  646  of the inner magnet assembly  600  and the magnet segments  710  of the outer magnet assembly  705  of the rotor assembly  700 . The alternating polarity of the magnet segments  646  creates an inner magnetic field, and the alternating polarity of the magnet segments  710  creates an outer magnetic field. These two magnetic fields synchronize together to provide a strong magnetic coupling torque between the inner magnet assembly  600  and the impeller assembly  700 , such that when the motor  6  is energized, it rotates the motor shaft  22 , which rotates the inner magnet assembly  600 , which in turn, rotates the impeller assembly  700 . 
         [0064]    Referring to  FIGS. 4 and 5 , the impeller  702  includes a plurality of vanes  740 . The casing  100  includes a discharge collector cavity  108  that is fluidly connected to the casing discharge port  102 . The rotation of the impeller vanes  740  causes a pumping action that moves liquid into the pump through the casing inlet port  104 , radially outward to the discharge collector cavity  108 , and out of the pump through the discharge port  102 . A portion of the vanes  740  of the rotor or impeller  702  extend forward in front of the front surface  509  of the nose cap  500  and inward to an inner diameter  744  that is smaller than an outer diameter  514  of the nose cap  500  of the canister assembly  400 . 
         [0065]    Referring to  FIG. 6 a   , the impeller  702  includes a rear wall  746  having a plurality of optional rear vanes  748 . As seen in  FIG. 3 , the casing  100  includes a rear cavity  110  that is partially blocked from the discharge collector cavity  108  by the impeller rear wall  746 . During pump operation, rotation of the impeller  702  rotates the fluid within the rear cavity  110 . The optional rear vanes  748  enhance or increase the speed of rotation of the fluid within the rear cavity  110  of the casing  100  which experiences centrifugal force. The centrifugal force will tend to create a radial pressure gradient in the rear cavity  110 , where the pressure is somewhat proportional to the radius. This gradient will partially resist the pressure differential that promotes the recirculation path P, and will reduce the overall pressure within the rear cavity  110 , to that the net forward thrust on the rotor assembly or impeller assembly  700  is reduced. 
         [0066]    When pump  2  is operating, the pumping action of the impeller vanes  740  creates a pressure differential within the pump  2 , such that the pressure at the inlet port  104  and in front of the nose cap  500  at the suction end of the pump  2  is lower than the pressure in the discharge collector cavity  108  and at the discharge port  102 . 
         [0067]    As may be seen in  FIG. 10  in a simplified view of the pump  2  without the drive magnet assembly or inner magnet assembly  600  and the power end drive components, the pump  2  includes a rather complex recirculation path P behind the impeller assembly  700 . The recirculation path P begins at the discharge collector cavity  108 , where the pressure is high, extends between stationary and rotating surfaces, and ends in front of the nose cap  500 , where the pressure is low. The recirculation path P is uniquely dynamic, because every portion of the path is bounded by a combination of a stationary surface and a rotating surface. This helps to avoid stagnation and clogging of the recirculation path P, which is used for lubrication and cooling of the pump components, such as the bushings and the canister assembly. The stationary surfaces are on the casing  100 , backplate  200 , and components of the canister assembly  400 , including the canister  400   a , rear thrust washer  814 , bearing sleeve  806 , front thrust washer  818  and nose cap  500 . The rotating surfaces are on the rotatable rotor assembly or impeller assembly  700 . The recirculation path P includes a radial gap between the canister  400   a  and the sleeve  712  of the rotor assembly or impeller assembly  700 . The one or more grooves  830  on the front face  822 , rear face  824  and inner surface  812  of the bushing  800  also facilitate fluid passage. 
         [0068]    The recirculation path P includes flow from the discharge collector cavity  108  past the outer edge of the impeller  702 . The fluid moves radially inward behind the impeller  702  and then further rearward behind the outer magnet assembly  705 . The fluid then moves forward along the canister portion extending through the radial gap between the canister and the outer magnet assembly  705 , and then the fluid passes radially inward over the canister to the bushing  800 . The fluid then passes through the grooves  830  that extend across the rear surface, inner surface and front surface of the bushing  800 . This example pump  2  includes four grooves  830  in the bushing  800 , and as a result, the fluid splits into four separate streams corresponding to the four grooves  830 . The four parallel paths continue through the grooves  830  to the front surface of the bushing  800 . The four flow paths come together at the front surface of the bushing  800  and then the fluid passes through a gap formed by the inner surface  727   b  of the impeller and both the outer surface of the front thrust washer  818  and the outer edges of the nose cap  500 , and to the low pressure area proximate the inlet port  104 . 
         [0069]    Referring to  FIGS. 11-13 , the same pump  2  of the first example is shown in a second example but connected to a different a rear end mechanical drive portion or power end and an adaptor. In this second example, the pump  2  is connected to a power end  900  and adapter  904  of a commercially available non-magnetically driven rotodynamic pump having a dynamic seal that is designed in accordance with dimensions specified in a pump industry standard, such as, for example, a Goulds 3196 Pump, made by ITT Goulds Pumps of Seneca Falls, N.Y., which is designed to meet the dimensioned required in industry standard ASME B73.1. This also applies to industry standard ISO 5199. The casing  100  is configured to be mounted in a stationary position and includes a rear face  106  that is connected to a flange  907  of the adapter  904  by use of a plurality of fasteners  10  that pass through apertures  912  in the flange  907  and engage threaded holes in the casing rear face  106 . 
         [0070]    In this second example, however, the pump  2  further includes an inner magnet assembly  600  that includes an inner ring  640  which is connected directly to a shaft  902  of the power end  900 . The inner ring  640  has a central threaded aperture  642  and the power end shaft  902  has a mating externally threaded front portion  922 , which is used to connect the inner ring  640  to the power end shaft  902 . Thus, the example magnetically driven pump  2  can be substituted in place for a dynamically sealed pump and will provide or accommodate the same mounting dimensions that are shown in  FIG. 11  as including: the horizontal distance F between the front and rear mounting feet; the vertical distance D from the bottom of the front mounting feet to the center of the motor shaft  902  and center of the flange for the inlet port  104  at the front of the pump  2 ; the vertical distance X from the center of the motor shaft  902  and center of the flange for the inlet port  104  at the front of the pump  2  to the top surface of the flange for the discharge port  102 ; the horizontal distance from the center of the discharge port  102  to the front of the flange for the inlet port  104 ; the horizontal distances E 1  from the center of the inlet port  104  to the center of the mounting holes of the front mounting feet; the diameter H of the mounting holes in the front mounting feet; and the overall length CP of the pump  2  and power end. 
         [0071]    Turning to  FIGS. 14-21 , a third example pump  1002  is shown. The third example pump  1002  happens to be a magnetically driven, positive-displacement gear pump. The third example pump  1002  includes a casing  1100  that includes a front portion  1100   a  and a rear portion  1100   b  and a central portion  1100   c . The casing portions may be separate components that are connected together or portions may be formed integrally, such as by casting. The casing  1100  is configured to be mounted in a stationary position via mounting feet on the central portion  1100   c . The casing  1100  also has a discharge port  1102  and an inlet port  1104 . In this third example, the discharge port  1102  and inlet port  1104  both are radially facing, although alternative configurations may be utilized. The casing  1100  may be constructed of rigid materials, such as steel, stainless steel, cast iron or other metallic materials, or structural plastics or the like. 
         [0072]    The rear portion  1100   b  of the casing  1100  includes an opening  1107  that receives one or more bushings or bearings  1120 , shown in the present example in the form of bearings. Also within the rear portion  1100   b  is a shaft  1130 . The shaft  1130  has a drive end  1132  that may be coupled to a driver (not shown), such as an electric motor or the like, that causes the shaft  1130  to rotate. As such, the example shaft  1130  is supported by the bushings or bearings  1120  and is free to rotate within the opening  1107  of the rear portion  1100   b  of the casing  1100 . 
         [0073]    The shaft  1130  may be constructed of rigid materials, such as steel, stainless steel, cast iron or other metallic materials, or structural plastics or the like. The shaft  1130  also may have a magnet receiving end  1134  that may include one or more holes  1136 , which in this example are threaded, but it will be understood that other configurations may be used for connecting components to the magnet receiving end  1134 . 
         [0074]    An example rotatable drive magnet assembly or inner magnet assembly  1200  is attached to the magnet receiving end  1134  of the shaft  1130 . The inner magnet assembly  1200  may include an inner ring  1210  having a generally cylindrical shape, one or more fasteners  1220  for connection to the receiving end  1134 , a plurality of (two or more) inner magnet segments  1230  and an optional inner magnet sleeve  1240 . The optional inner magnet sleeve  1240  may provide additional attachment force to hold the inner magnet segments  1230  to an outer surface  1211  of the inner ring  1210  and may provide protection of the inner magnet segments  1230  from corrosion or damage. The inner magnet sleeve  1240  may be constructed of rigid materials, but preferably is constructed of a material with very low magnetic permeability, such as stainless steel or the like. The method of connection for the inner magnet segments  1230  may be via adhesive, mechanical fasteners or other suitable means of connection. The magnet segments  1230  are radially charged and are positioned with alternating polarity, so as to create a magnetic field directed radially outward. 
         [0075]    The example inner ring  1210  may have a web  1250  that in this example engages the magnet receiving end  1134  of the shaft  1130 , and one or more holes  1260  that align with holes  1136  in the magnet receiving end  1134  of the shaft  1130  and receive the fasteners  1220 . In the present example, the inner ring  1210  may be connected to and rotate with the magnet receiving end  1134  of the shaft  1130 . The inner ring  1210  may be constructed of rigid materials, but is preferably constructed of a material with high magnetic permeability, such as iron, carbon steel or the like. It also will be understood that the inner ring  1210  may be connected to the shaft  1130  in alternative ways. 
         [0076]    The casing  1100  includes an opening  1109 , which in this example is in the central portion  1100   c . The opening  1109  receives a canister assembly  1300  that is intended to be stationary. The canister assembly  1300  may be constructed of multiple pieces or may be of an integral, one-piece construction. The canister assembly  1300  may be constructed of rigid materials. It will be appreciated that common materials may be used, such as stainless steel, or low conductivity metals, such as alloy C-22 or alloy C-276, and it could be advantageous to use materials having very low electrical conductivity, such as silicon carbide, ceramic, polymers or the like. The stationary canister assembly  1300  includes a canister  1301  having a rear flange  1302  that extends radially outward and is held between the connection of the rear portion  1100   b  to the central portion  1100   c  of the casing  1100 . A rear canister seal  1310  creates a leak-tight connection between the radial rear flange  1302  of the canister  1301  and the central portion  1100   c  of the casing  1100 . The rear canister seal  1310 , may be in the form of static seal having a resilient O-ring shape, or a preformed or liquid gasket or the like, and preferably is constructed of an elastomeric material such as rubber or the like. 
         [0077]    The canister  1301  of the canister assembly  1300  also includes a first cylindrical portion  1303  extending forward from the rear flange  1302  to a central radially extending portion  1304  that extends outward from the first cylindrical portion  1303  to a second cylindrical portion  1305  that extends further forward and is closed at the forward end by an end wall  1306 . The end wall  1306  is set back from the front end of the second cylindrical portion  1305 , forming a recess  1307  at the front of the canister  1301 . 
         [0078]    The canister assembly  1300  also includes a nose cap  1330  having a rear portion  1331  that engages the recess  1307  at the front of the canister  1301 . The nose cap  1330  of the canister assembly  1300  also has a flange  1332  that extends radially outward. A rear surface  1334  of the flange  1332  provides a first or forward axial bearing surface of the canister assembly  1300 . The central radially extending portion  1304  of the canister  1301  has a front surface  1308  that provides a second or rearward axial bearing surface of the canister assembly  1300 . The nose cap  1330  may be constructed of rigid materials, such as steel, stainless steel, cast iron or other metallic materials, or structural plastics or the like. A front canister seal  1320 , such as in the form of static seal having a resilient O-ring shape, or a preformed or liquid gasket or the like, creates a leak-tight connection between the canister  1301  and the nose cap  1330 , and may be constructed of similar materials to those mentioned with respect to the rear seal  1310 . The stationary canister assembly  1300  separates an internal fluid chamber within the pump  1002  from the inner magnet assembly  1200 . It also will be appreciated that any of the bearing surfaces of the canister assembly  1300 , such as the radial bearing surface provided by the second cylindrical portion  1305 , the first or forward axial bearing surface provided by the rear surface  1334  of the flange  1332  of the nose cap  1330 , and the second or rearward axial bearing surface provided by the front surface  1308  of the central radially extending portion  1304  of the canister  1301  alternatively could be provided by separate pieces, such as in the first example pump  2 . 
         [0079]    The front portion  1100   a  of the casing  1100  has a rear face that is sealed by a gasket  1108  to a front face of the central portion  1100   c  and closes the opening  1109  in the central portion  1100   c . The gasket  1108  may be in the form of a static seal, such as a preformed or liquid gasket or the like, or an O-ring, and creates a leak-tight connection between the front portion  1100   a  and central portion  1100   c , and may be constructed of similar materials to those mentioned with respect to the other seals. In this example, the front portion  1100   a  also has an inner surface  1109   a  that generally is aligned with the opening  1109  of the central portion  1100   c  of the casing  1100 . The front portion  1100   a  may be constructed of rigid materials, such as steel, stainless steel, cast iron or other metallic materials, or structural plastics or the like. 
         [0080]    The front end of the central portion  1100   c  has one or more holes  1113 , which in this example are threaded. The front portion  1100   a  is connected to the central portion  1100   c  by one or more fasteners  1360 . In the present example, an elongated shaft portion of the one or more fasteners  1360 , which in this example is threaded, is assembled through one or more holes  1106  in the front portion  1100   a  and is installed in the one or more holes  1113  in the front of the central portion  1100   c  of the casing  1100 . It also will be understood that the front portion  1100   a  may be connected to other portions of the casing  1100  in alternative ways. 
         [0081]    The nose cap  1330  of the canister assembly  1300  includes a front face  1333  that engages the front portion  1100   a . The nose cap  1330  also includes a front gear support extension  1336 , from which a further nose cap support extension  1338  extends. At least a portion of the nose cap support extension  1338  is received by an opening  1112  in the front portion  1100   a . The front nose cap support extension  1338  of the canister nose cap  1330  may include an alignment surface or shape that engages with a complementary surface or shape within the front portion  1100   a , such that when the nose cap support extension  1338  is received in the opening  1112  of the front portion  1100   a , the canister assembly  1300  is supported at its front end by the front portion  1100   a  of the casing  1100  and the engagement of the alignment surface or shape prevents relative rotation between nose cap  1330  and the front portion  1100   a . It will be understood that alternative methods and configurations may be used to prevent relative rotation between the respective components, so that the canister assembly  1300  remains stationary. Although not required, an optional seal, such as in the form of static seal having a resilient O-ring shape, or a preformed or liquid gasket or the like, may be located between the nose cap front portion  1100   a  to prevent pumped fluids from entering the opening  1112  in the front portion  1100   a . Such a seal may be constructed of similar materials to those mentioned with respect to the other seals. 
         [0082]    A rotatable rotor assembly or outer gear assembly  1500  includes a rotor  1501  having an outer gear  1510  at a forward end and an opening  1520  at the rearward end that receives an outer ring  1530 , a plurality of (two or more) outer magnet segments  1540 , and an optional inner magnet sleeve  1550 . In this way, the rotor assembly  1500  includes a rear opening  1520  having an inner wall surface  1521  to which a plurality of magnet segments  1540  is connected. The rotor  1501  may be constructed of rigid materials, such as steel, stainless steel, cast iron or other metallic materials, or structural plastics or the like. The outer ring  1530  may be constructed of rigid materials, but preferably is constructed of a material with high magnetic permeability, such as iron, carbon steel or the like. The outer ring  1530  is connected in the opening  1520 , which may be accomplished by various means, including by interference fit, adhesive, welding, the use of fasteners or the like. 
         [0083]    The outer ring  1530  includes an inner surface to which a plurality of (two or more) outer magnet segments  1540  are connected. It will be appreciated that the quantity of outer magnet segments  1540  should be equal to the quantity of the inner magnet segments  1230  that are connected to the inner ring  1210 . The method of connection for the outer magnet segments  1540  may be via adhesive (preferred), mechanical fasteners or other suitable means of connection. The outer magnet segments  1540  are magnetically radially charged and are positioned with alternating polarity, so as to create a magnetic field directed radially inward. The optional inner magnet sleeve  1550  may provide additional attachment force to hold the outer magnet segments  1540  to the outer ring  1530  and may provide protection of the outer magnet segments  1540  from corrosion or damage. 
         [0084]    The stationary first cylindrical portion  1303  of the canister assembly  1300  is located in a radial gap between the magnet segments  1230  of the inner magnet assembly  1200  and the magnet segments  1540  of the rotatable rotor assembly or outer magnet assembly  1500 . The magnet segments  1230  of the inner magnet assembly  1200  also are in axial alignment with the magnet segments  1540  of the rotor assembly or outer magnet assembly  1500 . The stationary first cylindrical portion  1303  of the canister assembly  1300  is located in a radial gap between the magnet segments  1230  of the inner magnet assembly  1200  and the magnet segments  1540  of the outer magnet assembly of the rotor assembly  1500 . The alternating polarity of the magnet segments  1230  creates an inner magnetic field, and the alternating polarity of the magnet segments  1540  creates an outer magnetic field. These two magnetic fields synchronize together to provide a strong magnetic coupling torque between the inner magnet assembly  1200  and the rotating rotor assembly  1500 . In addition, the canister assembly  1300  includes a front portion extending from the first cylindrical portion, which in this example also includes a second cylindrical portion  1305  which essentially extends from the first cylindrical portion and includes a radial bearing surface, as well as a nose cap  1330 , which includes a first axial bearing surface  1334  on the rear of the flange  1332 . 
         [0085]    The rotatable rotor assembly  1500  is positioned within the central portion  1100   c  and front portion  1100   a  of the casing  1100  and includes a rotor bushing  1560 . The rotor  1501  having the outer gear  1510  may be constructed of rigid materials, such as steel, stainless steel, cast iron or other metallic materials, or structural plastics or the like. The rotor bushing  1560  includes a front surface  1562  that provides a first or forward axial bearing surface and a rear surface  1564  that provides a second or rearward axial bearing surface. The rotor bushing  1560  further includes an inner wall surface  1566  that serves as a central cylindrical opening for the rotor assembly  1500  and provides a radial bearing surface for the rotor assembly  1500 . 
         [0086]    The inner surface  1566  of the bushing  1560  of the rotor assembly or outer gear assembly  1500  provides a radial bearing surface that slidingly rotates on and is supported by the second cylindrical portion  1305  of the canister  1301  of the canister assembly  1300 . The first or forward axial bearing surface provided by the front surface  1562  of the bushing  1560  slidingly rotates against or engages the first or forward axial bearing surface provided by the rear surface  1334  of the flange  1332  of the canister assembly  1300 . The second or rearward axial bearing surface provided by the rear surface  1564  of the bushing  1560  slidingly rotates against or engages the second or rearward axial bearing surface provided by the front surface  1308  of the central radially extending portion  1304  of the canister  1301  of the canister assembly  1300 . Thus, the bushing  1560  is of single piece construction and provides all of the bearing surfaces for the rotor assembly  1500 . 
         [0087]    Indeed, the radial bearing surface  1566  of the rotatable rotor assembly  1500  and the radial bearing surface provided by the outer surface of the second cylindrical portion  1305  of the canister assembly front portion restrict radial motion of the rotor assembly  1500 , and the first axial bearing surface  1562  of the rotor assembly  1500  and the first axial bearing surface  1334  of the nose cap  1330  restrict forward motion of the rotor assembly  1500 . In addition, the rotor assembly  1500  further comprises a second axial bearing surface  1564 , the canister assembly front portion further comprises a second axial bearing surface  1308 , and the second axial bearing surface of the rotor assembly  1564  and the second axial bearing surface  1308  of the front portion of the canister assembly  1300  restrict rearward motion of the rotor assembly  1500 . 
         [0088]    A rotatable drive magnet assembly or inner gear assembly  1600  includes inner gear  1610  that is positioned within the front portion  1100   a  of the casing  1100 . The inner gear  1610  may be constructed of rigid materials, such as steel, stainless steel, cast iron or other metallic materials, or structural plastics or the like. Although not required, the inner gear assembly  1600  also may include an optional inner gear bushing  1620 , which has an outer surface  1622  that may be connected to an inner surface  1612  of the inner gear  1610  by various means, including by interference fit, adhesive, welding, the use of fasteners or the like. The inner gear bushing  1620  also has an inner surface  1624  that provides a radial bearing surface for the inner gear  1610  as it slidingly rotates on the front gear support extension  1336  of the nose cap  1330  of the canister assembly  1300 . 
         [0089]    Pump operation comes from rotational energy that is supplied by a driver (not shown), such as an electric motor or the like, that is connected to the drive end drive end  1132  of the shaft  1130 . Thus, rotation of a driver or motor that is connected to the drive end  1132  causes the shaft  1130  to rotate. The inner magnet assembly  1200  is connected to, and therefore, rotated by the shaft  1130 . The radially outward magnetic field of the inner magnet segments  1230  rotates along with inner magnet assembly  1200 . In turn, the radially outward magnetic field of the inner magnet segments  1230  interacts with the radially inward magnetic field of the outer magnet segments  1540 , such that it drives the rotor assembly or outer gear assembly  1500  to rotate synchronously with inner magnet assembly  1200 , even though there is no physical contact between the outer gear assembly  1500  and the inner magnet assembly  1200 . 
         [0090]    The outer gear  1510  includes a plurality of (in this instance three or more) teeth  1517  that mesh with a plurality of teeth  1613  of the inner gear  1610 . Rotation of the outer gear assembly  1500  causes engagement of the surfaces of the outer gear teeth  1517  with the surfaces of the inner gear teeth  1613 , thereby causing the inner gear assembly  1600  to rotate. 
         [0091]    The front portion  1100   a  of the casing  1100  provides a pumping cavity that is connected to a discharge port  1102  and an inlet port  1104 . As the outer gear assembly  1500  and inner gear assembly  1600  rotate, the unmeshing of their teeth  1517  and  1613 , respectively, causes an expanding first pumping pocket that pulls fluid into it from the inlet port  1104 . As the outer gear assembly  1500  and inner gear assembly  1600  rotate further, the first pumping pocket moves clockwise until the teeth  1517  and  1613 , respectively, begin to remesh, which causes the pumping pocket to collapse, forcing the fluid to be discharged out of the pump  1002  through discharge port  1102 . 
         [0092]    When pump  1002  is operating, the pumping action creates a pressure differential within the pump  1002 , such that the pressure at the inlet port  1104  proximate the inner gear  1610  and nose cap  1330  at the suction end of the pump  1002  is lower than the pressure in the discharged fluid at the discharge port  1102 . As may be seen in  FIG. 21  in a simplified view of the pump  1002  without the inner magnet assembly  1200 , the rear portion  1100   b  of the casing  1100 , or the power end drive components, the pump  1002  includes a rather complex recirculation path P′ that extends behind the rotor assembly or outer gear assembly  1500 . The recirculation path P′ begins at the discharge portion of the casing  1100  that forms the discharge port  1102 , where the pressure is high, extends between stationary and rotating surfaces, and ends in front of the nose cap  1300 , where the pressure is low. 
         [0093]    The recirculation path P′ is uniquely dynamic, because every portion of the path is bounded by a combination of a stationary surface and a rotating surface. This helps to avoid stagnation and clogging of the recirculation path P′, which is used for lubrication and cooling of the pump components, such as the bushings and the canister assembly. The stationary surfaces are on the casing  1100  and components of the canister assembly  1300 , including the radial rear flange  1302 , the first cylindrical portion  1303 , the central radially extending portion  1304 , the second cylindrical portion  1305 , and the nose cap  1330 . The rotating surfaces are on the rotor assembly or outer gear assembly  1500  and the inner gear assembly  1600 . 
         [0094]    The recirculation path P′ includes a longitudinal groove  1122  in the discharge side of the front portion  1100   a  of the casing that allows fluid to pass around a forward portion of the rotor assembly or outer gear assembly  1500 , which otherwise has a close clearance fit with the front portion  1100   a . The outer diameter of the rotor assembly  1500  is reduced rearward of the front portion, increasing the clearance between the rotor assembly  1500  and the central portion  1100   c  of the casing  1100 . When the fluid from the groove  1122  in the front portion  1100   a  enters this area of greater clearance, it spreads out all the way around the rotor  1501  and into a cylindrical gap between the rotor assembly  1500  and the central portion  1100   c  of the casing  1100 , and continues to move rearward. The recirculation path P′ continues behind the rotor assembly  1500  and along the radial rear flange  1302  of the canister  1301 , then moving forward along the first cylindrical portion  1303  and radially inward along the central radially extending portion  1304  of the canister  1301  and the rear surface  1564  of the bushing  1560  that provides the second or rearward axial bearing surface of the rotor assembly  1500 . The rear surface  1564  of the bushing  1560  has a close clearance fit to the rear flange  1302 , but the rear surface  1564  also includes a plurality of grooves  1570  that extend across surfaces of the bushing  1560 , including the rear surface  1564  that provides a second or rearward axial bearing surface, inner surface  1566  that provides a radial bearing surface, and front surface  1562  that provides a first or forward axial bearing surface of the bushing  1560 . This example pump  1002  includes four grooves  1570  in the bushing  1560 , and as a result, the fluid splits into four separate streams corresponding to the four grooves  1570  as it passes over the axial and radial bearing surfaces of the bushing  1560 . The four parallel paths continue through the grooves  1570  to the front surface  1562  of the bushing  1560 . The four flow paths from the grooves  1570  come together at the front surface  1562  and meet an outer corner of the flange  1332  of the nose cap  1330 , where a small donut shaped cavity  1574  is formed by a circumferential groove  1576  in the inner surface  1572  of the rotor  1501 , a circumferential groove on the outer rear corner of the flange  1332  of the nose cap  1330 , and a circumferential groove  1578  on the outer front edge of the bushing  1560 . Continuing in the path P′, the radial flange  1332  of the nose cap  1330  has a close clearance fit with the inner surface  1572  of the rotor, but fluid is permitted to pass through a groove  1340  that extends longitudinally along the outer edge of the flange  1332  and then radially inward across the front face  1333  of the nose cap  1330 . The groove  1340  leads the fluid flow to a flat surface  1342  in the front gear support extension  1336 , which permits fluid to flow forward between the front gear support extension  1336  and the inner gear bushing  1620 , to a groove  1124  in the front portion  1100   a  of the casing  1100 . This further groove  1124  allows the fluid to flow through to the suction side at the inlet port  1104 , completing the recirculation path P′ of the pump  1100 . 
         [0095]    From the above disclosure, it will be apparent that pumps constructed in accordance with this disclosure may include a number of structural aspects that provide advantages over conventional constructions, depending upon the specific design chosen. 
         [0096]    It will be appreciated that pumps constructed in accordance with the present disclosure may be provided in various configurations. Any variety of suitable materials of construction, configurations, shapes and sizes for the components and methods of connecting the components may be utilized to meet the particular needs and requirements of an end user. Indeed, pumps in accordance with the present disclosure may include interior surfaces that are constructed of specific materials and/or have particular surface finishes wherein the interior surfaces permit use of the pumps in hygienic applications where microbial growth must be prevented. It will be apparent to those skilled in the art that various modifications can be made in the design and construction of such pumps without departing from the scope or spirit of the claimed subject matter, and that the claims are not limited to the preferred embodiment illustrated herein. It also will be appreciated that some aspects of the example embodiment are discussed in a simplified manner and the aspects may be capable of being implemented in rotodynamic pumps, positive-displacement pumps, and whether such pumps include dynamic seals between rotating parts or are magnetically driven.