US20050036895A1

US20050036895A1 - Canned motor and pump

Info

Publication number: US20050036895A1
Application number: US10/638,615
Authority: US
Inventors: David Tremain; Gregory Rittgers
Original assignee: MTH Tool Co Inc
Current assignee: MTH Tool Co Inc
Priority date: 2003-08-11
Filing date: 2003-08-11
Publication date: 2005-02-17

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

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

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.
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.
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.
The present invention is intended to overcome one or more of the above problems.

SUMMARY OF THE INVENTION

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.
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.
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.
In a highly preferred embodiment, the shaft is a NEMA standard JM extended shaft.
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.
A preferred embodiment contemplates the presence of an annular seal between the noses at their interface.
In a highly preferred embodiment, the second nose has an annular, interior surface at least partially defining the seal cavity.
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.
Preferably, the return path includes a bore in the shaft.
Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings.

DESCRIPTION OF THE DRAWING

The Figure is a sectional view of a motor and pump assembly made according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.

Claims

1. A canned motor and pump combination comprising:

a motor housing;

a motor stator within said motor housing having a generally cylindrical motor rotor receiving opening;

a thin walled cylindrical can snugly received in said rotor receiving opening and having opposed open ends;

a motor rotor received within said can and having a generally cylindrical outer surface located just radially inward of an interior surface of said can to define a small annular gap;

a NEMA standard JM extended shaft impaling said motor rotor and extending axially from both sides of said motor rotor;

end closures closing and sealed to respective ends of said can;

bearings mounted to said end closures to provide journaling for said shaft and to resist thrust loads imparted to said shaft;

a pump housing mounted to one end of said motor housing and sealed thereto, said pump housing including a rotor cavity and a seal cavity intended to receive a mechanical seal for a shaft;

a pump rotor within said rotor cavity;

said NEMA standard JM extended shaft having an end opposite said motor housing one end received in one of said bearings supported by one end closure thereat and an opposite end extending from said motor housing one end through said seal cavity into said rotor cavity and mounting said pump rotor therein, said opposite end being received in another of said bearings supported by an end closure at said housing one end;

said seal cavity being characterized by the absence of a mechanical seal whereby fluid in said pump cavity may flow therefrom through said another bearing, about said motor rotor through said gap while being contained by said can and through said one bearing to a return path to said pump cavity; and

said one end closure further sealing said can opposite end except for said return path.

2. The canned motor and pump combination of claim 1 wherein said motor housing and said pump housing are joined at an interface, said interface including a first nose extending axially from said motor housing toward said pump housing and about said shaft and a second nose extending axially from said pump housing toward said motor housing about said shaft, said noses being in tight telescoping relation with one another.

3. The canned motor and pump combination of claim 2 further including an annular seal between said noses at said interface.

4. The canned motor and pump combination of claim 3 wherein said second nose has an annular interior surface at least partially defining said seal cavity.

5. The canned motor and pump combination of claim 3 wherein one of said noses includes an interior stepped surface and the other of said noses includes an exterior stepped surface and said annular seal is disposed between and sealingly engages said stepped surfaces.

6. The canned motor and pump combination of claim 1 wherein said return path includes a bore in said NEMA standard JM extended shaft.

7. A canned motor and pump combination comprising:

a motor housing;

end closures closing and sealed to respective ends of said can;

a pump housing mounted to one end of said motor housing and sealed thereto at an interface with said interface including a first nose extending axially from said motor housing toward said pump housing and about said shaft and a second nose extending axially from said pump housing toward said motor housing about said shaft, said noses being in tight telescoping relation with one another, and a rotor cavity within said pump housing including a seal cavity intended to receive a mechanical seal for a shaft, said rotor cavity being located at least in part in said second nose;

a pump rotor within said rotor cavity;

said NEMA standard JM extended shaft having an end opposite said motor housing one end received in one of said bearings supported by one end closure thereat and an opposite end extending from said motor housing one end into said rotor cavity through said seal cavity and mounting said pump rotor in said rotor cavity, said opposite end being received in another of said bearings supported by an end closure at said housing one end;

said seal cavity being characterized by the absence of a mechanical seal whereby fluid in said pump cavity may flow therefrom through said another bearing, about said rotor shaft through said gap while being contained by said can and then through said one bearing;

a return path for fluid including a bore in said shaft extending to said pump cavity; and

said one end closure further sealing said can opposite end.

8. The canned motor and pump combination of claim 7 wherein one of said noses includes an interior step surface and the other of said noses includes an exterior step surface and an annular seal disposed between and sealingly engaging said step surfaces.

9. A canned motor and pump combination comprising:

a motor housing;

a shaft impaling said motor rotor, said shaft including a nominally central section on which said motor rotor is mounted, bearing receiving sections on each side of said nominally central section, and a seal mounting section to a side of one bearing receiving section remote from said nominally central section and intended to mount a mechanical seal and terminating in a pump rotor mounting end;

end closures closing and sealed to respective ends of said can;

bearings mounted to said end closures to provide journaling for said shaft and to resist thrust loads imparted to said shaft and received on respective ones of said bearing receiving sections;

a pump housing mounted to one end of said motor housing and sealed thereto, said pump housing including a rotor cavity and a seal cavity intended to receive a mechanical seal for a shaft, said rotor cavity surrounding said pump rotor receiving end and said seal cavity surrounding said seal mounting section of said shaft;

a pump rotor within said rotor cavity;

said seal cavity and said seal mounting section of said shaft being characterized by the absence of a mechanical seal whereby fluid in said pump cavity may flow therefrom through said another bearing, about said motor rotor through said gap while being contained by said can and through said one bearing to a return path to said pump cavity; and

10. The canned motor and pump combination of claim 9 wherein said nominally central section and said bearing receiving section are separated by annular shoulders on said shaft and said seal mounting section is separated at said side of said one bearing receiving section by a shoulder and together with said pump rotor mounting end being of reduced diameter in relation to the remainder of said shaft.

11. A canned motor and pump combination comprising:

a motor housing;

a shaft impaling said motor rotor, said shaft including a nominally central section on which said motor rotor is mounted, bearing receiving sections on each side of said nominally central section, and a seal mounting section of reduced diameter to a side of one bearing receiving section remote from said nominally central section and intended to mount a mechanical seal and terminating in an end adapted to be keyed to a pump rotor to mount a pump rotor within a pump cavity within a pump housing;

end closures closing and sealed to respective ends of said can;

a pump rotor within said rotor cavity;

said seal cavity and said seal mounting section of said shaft being characterized by the absence of a mechanical seal whereby fluid in said pump cavity may flow therefrom through said another bearing, about said motor rotor through said gap while being contained by said can and through said one bearing to a return path to said pump cavity; and said one end closure further sealing said can opposite end except for said return path.