Abstract:
The expense of canned motor and pump assemblies for use in pumping liquids in systems requiring complete liquid containment is minimized in a construction whereby standard pump constructions may be coupled to a canned motor. The invention contemplates utilizing a NEMA standard JM extended shaft for journaling the motor rotor, which shaft extends into the conventional seal cavity of any one of a variety of different types or sizes of rotary driven pumps to be coupled to the rotor therein without the use of a mechanical seal in the pump seal cavity.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to canned motor and pump combinations, and more particularly, to a canned motor that may be fitted with any one of a large variety of standard pump constructions.  
       BACKGROUND OF THE INVENTION  
       [0002]     So-called “canned motors” are frequently employed as a power source for pumps handling liquids in systems where complete containment of the liquid is required or at the very least, highly desirable. In such systems, potentially hazardous fluids are transported and because of their nature, spillage of the liquid for any reason is definitely to be avoided. As a consequence, conventional motors and pump assemblies are to be avoided because of the need for a seal, either a mechanical seal or packing, near the point of connection of the motor shaft to the pump rotor within the pump housing.  
         [0003]     As with any mechanical instrumentality having relatively movable parts, over a period of use, wear will occur between the relatively moving parts and motor driven pumps are no exception. The wear that occurs at the seal may result in the formation of a leakage path, allowing the liquid being pumped to spill from the motor and pump construction and enter the surrounding environment. Clearly, this is highly undesirable where the liquid being pumped is of a potentially hazardous nature; and this has necessitated use of so-called canned motors as referred to above where the rotor of the motor is contained in a can and the liquid being pumped allowed to enter the rotor receiving space of the motor to be contained therein. Typically, some provision for return of the liquid entering the rotor cavity of the motor to the pumping system is provided as well.  
         [0004]     This type of construction has provided a solution to the problem of unwanted spillage of liquids due to seal deterioration over time. However, the solution is not an inexpensive one, and heretofore has required the design and manufacture of specific pumps for specific canned motors. That is to say, it has not been feasible to provide a specific canned motor for use with a large variety of existing pump designs to achieve a lower cost assembly.  
         [0005]     The present invention is intended to overcome one or more of the above problems.  
       SUMMARY OF THE INVENTION  
       [0006]     It is the principal object of the invention to provide a new and improved canned motor and pump assembly. More specifically, it is an object of the invention to provide a canned motor which can be readily coupled to any of a large variety of standard pump constructions to provide the benefits of reliable containment of the liquid being pumped even after extended use and the accompanying wear.  
         [0007]     An exemplary embodiment of the invention achieves the foregoing object in a canned motor and pump combination that includes a motor housing. A motor stator is located within the motor housing and has a generally cylindrical rotor receiving opening. A thin walled cylindrical can is snugly received in the rotor receiving opening and has opposed ends. A motor rotor is received within the can and has a generally cylindrical outer surface located just radially inward of an interior surface of the can to define a small annular gap. A shaft impales the motor rotor and the shaft includes a nominally central section on which the motor rotor is mounted. Bearing receiving sections are located on the shaft on each side of the nominally central section and a seal mounting section is located to a side of one of the bearing receiving sections remote from the nominally central section and which is intended to mount a mechanical seal. The seal mounting section terminates in a pump rotor mounting end. End closures are provided to close and seal respective ends of the can and bearings are mounted to the end closures to provide journaling for the shaft and to resist thrust loads imparted to the shaft. The bearings are received on respective ones of the bearing receiving sections on the shaft. A pump housing is mounted to one end of the motor housing and sealed thereto. The pump housing includes a rotor cavity and a seal cavity intended to receive a mechanical seal for a shaft. The rotor cavity surrounds the pump rotor receiving end of the motor shaft and the seal cavity surrounds the seal mounting section of the shaft. A pump rotor is disposed within the rotor cavity. The seal cavity and the seal mounting sections of the shaft are characterized by the absence of a mechanical seal whereby fluid in the pump cavity may flow therefrom through the adjacent bearing, about the motor rotor through the gap, while being contained by the can and through the one bearing to a return path to the pump cavity. The end closure at the one bearing further seals the can opposite end except for the return path.  
         [0008]     In a preferred embodiment, the nominally central section and the bearing receiving sections are separated by annular shoulders on the shaft and the seal mounting section is separated at the side of the one bearing receiving section by a shoulder and together with the pump rotor mounting end is of reduced diameter in relation to the remainder of the shaft.  
         [0009]     In a highly preferred embodiment, the shaft is a NEMA standard JM extended shaft.  
         [0010]     The invention contemplates, in a highly preferred embodiment, that the motor housing and the pump housing be joined at an interface that includes a first nose extending axially from the motor housing toward the pump housing and about the shaft and a second nose extending axially from the pump housing toward the motor housing about the shaft. The noses are in tight telescoping relation with one another.  
         [0011]     A preferred embodiment contemplates the presence of an annular seal between the noses at their interface.  
         [0012]     In a highly preferred embodiment, the second nose has an annular, interior surface at least partially defining the seal cavity.  
         [0013]     A preferred embodiment also contemplates that one of the noses includes an interior stepped surface and the other of the noses includes an exterior stepped surface. The annular seal is disposed between and sealingly engages the stepped surfaces.  
         [0014]     Preferably, the return path includes a bore in the shaft.  
         [0015]     Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings.  
     
    
     DESCRIPTION OF THE DRAWING  
       [0016]     The Figure is a sectional view of a motor and pump assembly made according to the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     An exemplary embodiment of a canned motor and pump assembly made according to the invention is illustrated in the Figure. The same includes an electric canned motor, generally designated  10 , coupled to a centrifugal pump, generally designated  12 . Referring first to the motor  10 , the same is seen to include a housing, generally designated  12  which contains a motor stator  14 , the end turns of which are shown at  16 . The stator  14  includes a cylindrical, generally central opening  18  for receipt of a rotor  20 . The rotor  20  is impaled on a shaft  22  which, in a highly preferred embodiment, is a NEMA standard JM extended shaft. The same includes a nominally central section  24  which receives the rotor  20  and which is flanked by bearing receiving sections  26 . The bearing receiving sections  26  are separated from the nominally central section  24  by small shoulders  28  such that the nominally central section  24  is of somewhat larger diameter than the bearing receiving sections  26 .  
         [0018]     As viewed in the Figure, the rightmost one of the bearing receiving sections  26 , on its side  30  remote from the nominally central section  24 , includes a seal mounting section  32  and in turn terminates in the pump rotor mounting end  34 . The seal mounting section  32  and the pump rotor mounting end  34 , at the end  30  of the rightmost bearing receiving section  26  are separated by a shoulder  36  such that the seal mounting section  32  and the end  34  are of reduced diameter in relation to the remainder of the shaft  22 .  
         [0019]     A thin walled can  38  that is in the form of an open ended hollow cylinder, is tightly fitted within the rotor receiving opening  18  of the stator  14  and in turn receives the rotor  20  such that a small, annular gap  40  exists between the two to allow the rotor  20  to rotate. The annular gap  40  is typically made as small as possible to minimize losses during motor operation.  
         [0020]     The motor housing  10  includes end caps  42  and  44 . The end cap  42  in turn mounts an end closure  46  which extends to the adjacent end  48  of the can  38  and is sealed thereto. The end closure  46  is somewhat bell-shaped and within its interior mounts a carbon fiber bearing  50  which is received on the left bearing receiving section  26  of the shaft  22  for journaling purposes. The bearing  50  includes four angularly spaced axial grooves  52  and a spirally extending groove  54  on its interior surface.  
         [0021]     Also mounted on the bearing receiving section  26  in abutment with the shoulder  28  as well as the bearing  50  is a thrust bearing  56 . The journal bearing  50  and thrust bearing  56  are also separated by a plurality of radially extending grooves  58  in an end face of the bearing  50 .  
         [0022]     The end cap  44  mounts a combination adapter and end closure  60  which mounts a journal bearing  62  about the rightmost bearing receiving section  26  of the shaft  22 . Abutted against the shoulder  28  adjacent the right-hand bearing receiving section  26  is a thrust bearing element  56  and it will be appreciated that the grooves  52 ,  54  and  58  are  25  provided in the journal bearing  62  in the same configuration as described earlier in connection with the journal bearing  50 .  
         [0023]     Returning to the end closure  46 , the same includes a bore  64  which is normally plugged by a plug (not shown) and as a consequence, it will be appreciated that the end closure  46  completely seals the left-hand end of the cylindrical can  38 . The interface of the end cap  44  and the end closure  60  is sealed by an annular O-ring seal and groove structure  66  and the end plate  44  and end closure  60  are held together by a series of threaded fasteners  68  (only one of which is shown) to slightly compress the seal to provide a good seal at that location.  
         [0024]     Oppositely of the journal bearing  62 , the end closure  60  includes an annular nose  70  having an internal, annular, stepped surface  72 . Adjacent the internal stepped surface  72 , there is also located a tapped port  74  for purposes to be seen.  
         [0025]     The pump  12  includes a housing, generally designated  80 , including a rotor receiving cavity  82  surrounded by a volute  84  extending to an outlet  86 . An inlet  88  is also included and disposed within the cavity  82  is a pump rotor  90 . As illustrated, the pump rotor  90  is of the radial discharge type but it should be appreciated that virtually any type of rotor employed in a centrifugal pump that matches its housing could be utilized.  
         [0026]     The pump rotor  90  includes a hub  92  provided with a bore  94  which receives the pump rotor receiving end of the shaft  22  and is secured thereon by a threaded fastener  96  provided with a through bore  98 . A key or spline  99  fixes the pump rotor  90  against rotation relative to the shaft  22 .  
         [0027]     Conventionally, the pump rotor  90  may also include a pressure  25  balance surface  100  which is in fluid communication by a small port  102  with the inlet side of the pump. The bore  98  is, in turn, in fluid communication with a central bore  104  in the shaft  22 .  
         [0028]     A spacing sleeve  106  is disposed on the seal mounting section  32  of the shaft  22  for the purpose of properly locating the rotor  90  within the pump rotor receiving cavity  82 . About the sleeve  106 , the pump housing includes a seal cavity  108  which is intended to receive a mechanical seal as would be used in a conventional rotor and pump assembly to seal the interface of the pump and the motor shaft. However, according to the invention, the cavity  108  is characterized by the absence of any mechanical seal therein and by the same token, the seal mounting section  32  of the shaft  22  is likewise characterized as lacking any mechanical seal mounted thereon.  
         [0029]     A so-called breakdown bushing  110  is mounted on an interior surface of the pump housing  82  and engages the spacing sleeve  106 . The breakdown bushing conventionally serves to limit the flow of the liquid being pumped between the port  74  and the seal receiving cavity  108 . In fact, the breakdown bushing  110  is generally not required in those constructions having a balance surface  100  connected by a bore  102  to the inlet side of the pump.  
         [0030]     Via a suitable fitting, a small section of conduit  112  is connected to the outlet  86  of the pump  12  and to the port  74  to establish fluid communication between the two.  
         [0031]     The pump  12  will conventionally include a mounting flange  114  by which the pump  12  may be mounted to the motor  10  by a series of threaded fasteners  116 , only one of which is shown.  
         [0032]     It will also be appreciated that an annular nose  118  on the pump housing  82  extends about the seal cavity  108  within the pump housing  82  extends toward the motor  10  and includes an exterior, annular, stepped surface  120 . As can be clearly seen in the Figure, the stepped surface  72  and  120  on the motor  10  and pump  12  respectively telescope into each other with the stepped surface  120  entering the stepped surface  72 . An O-ring seal  122  is located at the interface of the stepped surfaces  72  and  120 , thereby sealing the pump housing  82  to the end closure  60  of the motor  10 .  
         [0033]     In operation, the liquid to be pumped enters the pump  12  through the inlet  88  and is expelled through the outlet  86 . The conduit  112  is connected to the volute  84  adjacent the outlet  86  and as a consequence, liquid under high pressure from the outlet  86  will pass through the conduit  112  to the area between the journal bearing  62  and the breakdown bushing  110 . The liquid will flow through the axial grooves  52  and the spiral grooves  54  and then through the grooves  58  to the interior of the can  38 . It will then pass through the annular space  40  between the can  38  and the rotor  20  to the end  48  of the can  38 , all the while being contained by the end closures  46  and  60 . The fluid will continue to flow, first through the grooves  58  between the left-hand thrust bearing  56  and the journal bearing  50  to enter the axial and spiral grooves  52  and  54  to exit at the left-hand end of the shaft  24 . The liquid will then continue to flow through the internal bore  104  in the shaft  22  in a rightward direction as viewed in the Figure through the bore  98  in the fastener  96  to a low pressure area adjacent the inlet  88  of the pump.  
         [0034]     This provides continuous circulation of the liquid allowing the same to cool the electrical components of the system while all the while being contained in a path that is closed by the end closures  46  and  60  and the cylindrical can  38 .  
         [0035]     This containment is accomplished without the use of any mechanical seal in the cavity  108  and on the seal receiving surface  32  of the shaft  24  which is to say the containment function of a canned motor  10  coupled to a pump  12  is maintained.  
         [0036]     It will be further observed that the system is readily susceptible to the use of any of a variety of different sized or shaped pumps  12  with the motor illustrated in the Figure. At most, it may be necessary to machine the nose  118  on the pump  12  to provide the stepped surface  120  such that it telescopes within the nose  72  on the end closure  60  for the motor  10 . However, this is a relatively simple and inexpensive operation, the cost of which is more than compensated for by the fact that through the particular configuration of the shaft  22  as a NEMA standard JM extended shaft or equivalent as the shaft for the motor  10 , existing pumps do not have to be redesigned to be useable with a canned motor construction.