Magnetically coupled sealless centrifugal pump

Abstract

A magnetically driven centrifugal pump has a pump case, an open vane impeller in the pump case, a stuffing box including a stuffing box outer being fixed relative to the pump case and a stuffing box inner threadedly engaged with the stuffing box outer, and a rotor axially fixed and rotatably mounted in the stuffing box inner. Bushings are arranged between the rotor and the stuffing box inner. A drive is fixed relative to the pump case and includes a drive output extending into the rotor. There is a magnetic coupling between the rotor and the drive and a canister fixed to the stuffing box and extending through the magnetic coupling to isolate the rotor from the drive. A rub ring closes the end of the stuffing box inner and constrains the drive output from damaging the canister under catastrophic bearing failure.

Claims

1. A magnetically driven centrifugal pump having an axis of impeller rotation, the magnetically driven centrifugal pump comprising: a pump case; an open vane impeller in the pump case rotatably mounted about the axis of impeller rotation; a stuffing box including a stuffing box outer being fixed relative to the pump case and a stuffing box inner accessible from outside the pump to rotate the stuffing box inner, the stuffing box outer including a first thread fixed relative to the stuffing box outer and extending in a circumferential direction about the axis of impeller rotation, the stuffing box inner including a respective second thread threadedly engaged with the first thread and thereby forming a threaded connection with the first thread, the second thread fixed relative to the stuffing box inner and extending in the circumferential direction about the axis of impeller rotation; a rotor axially fixed and rotatably mounted about the axis of impeller rotation in the stuffing box inner, the impeller being fixed to rotate with the rotor, the rotor axially movable by the stuffing box inner as the stuffing box inner is rotated to adjust a clearance between the impeller and the pump case; a drive including a drive end rotatably mounted about the axis of impeller rotation, the drive end disposed at least partially inside the rotor; a magnetic coupling defined between an internal surface of the rotor and an external surface of the drive end; and a canister fixed to the stuffing box inner and extending between the drive and the rotor through the magnetic coupling to isolate the rotor from the drive and prevent a process fluid from flowing from the stuffing box to the drive.

2. The magnetically driven centrifugal pump of claim 1, wherein the rotor is concentric with and outwardly of the drive end at the magnetic coupling in the stuffing box.

3. The magnetically driven centrifugal pump of claim 2, further comprising: a journal rotor bushing between the rotor and the stuffing box inner; a journal impeller bushing aligned radially between the impeller and the stuffing box inner; and two opposed thrust bushings, a first of the thrust bushings being between and bearing on both the stuffing box inner and the rotor.

4. The magnetically driven centrifugal pump of claim 3, wherein the rotor defines, with the stuffing box inner, a process fluid shunt therebetween configured to direct the process fluid to the journal rotor bushing, lubricating the journal rotor bushing.

5. The magnetically driven centrifugal pump of claim 1, wherein the rotor comprises a mounting hub attached to an impeller hub of the impeller.

6. The magnetically driven centrifugal pump of claim 5, wherein the mounting hub comprises a shunt return bore configured to direct the process fluid from about the canister to the impeller.

7. The magnetically driven centrifugal pump of claim 6, wherein the rotor defines, with the stuffing box inner, a first gap therebetween configured to direct the process fluid from the impeller to a detachable cap of the stuffing box inner, and the rotor defines, with the canister, a second gap therebetween configured to direct the process fluid from the detachable cap of the stuffing box inner to the shunt return bore of the rotor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional elevation of a magnetically driven centrifugal pump taken through the axis of impeller rotation;

(2) FIG. 2 is a cross-sectional detail of the stuffing box illustrated in FIG. 1;

(3) FIG. 4 is a cross-sectional elevation of a second embodiment of a magnetically driven centrifugal pump taken through the axis of impeller rotation;

(4) FIG. 5 is a cross-sectional detail of the stuffing box illustrated in FIG. 4; and

(5) FIG. 6 is a detail of the magnets and bushings in the stuffing box of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) Turning in detail to the drawings, the Figures each show the surface of sections through the access of impeller rotation 10. The major components except for the pump case and the pump housing, which are asymmetrical because of volutes and mountings, respectively, are substantially symmetrical about the axis of impeller rotation. The first embodiment, FIGS. 1 through 3, differ from the second embodiment, FIGS. 4 through 6, by the support arrangements for the impeller. In both embodiments, a bushing is about the hub of the impeller to securely support the rotatable impeller.

(7) A pump case 12 defining an impeller cavity and a volute is further defined by a housing structure 13. The pump case 12 surrounds an open vane impeller 14 while the housing structure 13 extends over a stuffing box 16. The impeller 14 includes an impeller hub 15 extending away from the vanes of the impeller 14. The pump case 12 and housing structure 13 are conventionally assembled with bolts. The housing structure 13 is shown in this instance to have an open arrangement with holes about the circumference.

(8) The stuffing box 16 includes a stuffing box outer 18 which is a collar with an outer flange 19 engaging the pump case 12 and held in place by the housing structure 13. The stuffing box 16 further includes a stuffing box inner 20 engaged with the stuffing box outer 18 at a threaded engagement 22. The threaded engagement 22 provides for the stuffing box inner 20 to be rotated relative to the stuffing box outer 18 to allow axial translation of the stuffing box inner 20 relative to the stuffing box outer 18 and in turn the pump case 12. After the desired axial position of the stuffing box inner 20 is achieved, the rotational position of the stuffing box inner can either be held by thread friction or by an external set screw. The stuffing box inner 20 extends from the threaded engagement 22 as a cylinder to a stuffing box inner detachable cap 24. The stuffing box inner detachable cap 24 is held in place by fasteners.

(9) A rotor 26 is located within the annular cavity defined within the stuffing box inner 20. The rotor 26 is also cylindrical with a front wall. A mounting hub 27 fixed on the cylindrical front wall threadedly engages the impeller hub 15 so that the impeller 14 is detachably fixed to the rotor 26. With the rotor 26 located in the annular cavity with thrust bushings described below, the rotor 26 moves axially with the stuffing box inner 20 relative to the stuffing box outer 18. With the stuffing box outer 18 engaging the pump case 12 and the rotor 26 being engaged through the mounting hub 27 with the impeller hub 15, the axial adjustment of the stuffing box inner 20 relative to the stuffing box outer 18 is used to create an appropriate clearance between the impeller 14 and the pump case 12.

(10) A drive 28 is arranged inwardly of the rotor 26. The drive 28 includes a drive output 29 that is cylindrical with an engagement to receive a drive shaft coupled with a motor (not shown) for torque transfer. The drive further includes a drive shaft power frame 30 with a shaft conventionally arranged in with bearings as shown to transfer rotary power from the motor. The housing is conventionally coupled with the housing structure 13 by bolts.

(11) Power to the rotor 26 from the drive 28 is transmitted through a magnetic coupling 31. The magnetic coupling 31 is traditional including driving magnets 32 associated with the drive 28 and driven magnets 34 associated with the rotor 26. A canister 36 extends through the magnetic coupling. The canister 36 is integrally formed with the stuffing box inner detachable cap 24. The stuffing box inner detachable cap 24 and the associated canister 36 are retained by fasteners at the end of the stuffing box inner 20. Thus, the canister 36 does not rotate with either the rotor 26 or the drive 28 but remains stationary in the pump unless the impeller 14 is being axially adjusted. The canister 36 includes a concave end which results in less distortion of the canister 36 under pressure loads from the pump process fluids.

(12) In the preferred embodiment, the rotating components within the stuffing box 16 are mounted through bushings. The bushings used in these embodiments are bushing pairs each with a static bushing associated with the stuffing box inner 20 and a dynamic bushing each associated with the rotor/impeller assembly 26/14. These components are held in place by conventional means. An annular rotor bushing 38 is located between the stuffing box inner 20 and the rotor 26. The annular impeller bushing 40 is between the stuffing box inner 20 and the impeller hub 15. In the first embodiment as illustrated in FIGS. 1 through 3, the mounting hub 27 includes an outer ring 41. The annular impeller bushing 40 is engaged with the mounting hub 27. This arrangement thus allows engagement of all of the bushings with the rotor 26. At the same time, the annular impeller bushing 40 remains between the stuffing box inner 20 and the impeller hub 15 to positively mount the impeller 14. In the second embodiment, as seen in FIGS. 4 through 6, the bushing 48 directly engages the impeller hub 15 to the same end. With either arrangement, the rotor 26 is rotationally mounted by the annular rotor bushing 38 and the annular impeller bushing 40 within the stuffing box inner 20.

(13) A forward thrust bushing 42 is arranged between the stuffing box inner detachable cap 24 and the rotor 26. A rearward thrust bushing 44 is located between the stuffing box wall 25 and the rotor 26. The thrust bushings 42, 44 thus retain the rotor 26 fixed axially within the stuffing box inner 20. Again, all of the annular and thrust bushings are traditionally placed within the pump.

(14) A process fluid shunt 46 lubricates the bushings located about the rotor. A shunt inlet 48 is located outwardly of the impeller hub 15 to extend through the annular impeller bushing 40. A gap between the rotor 26 and the stuffing box wall 25 directs process fluid through the rearward thrust bushing 44. An annular gap between the stuffing box inner 20 and the rotor 26 then permits the shunted process fluid to move to and through the annular rotor bushing 38. An annular cavity adjacent the annular rotor bushing 38 defined in the stuffing box inner detachable cap 24 then directs the shunted process fluid through the forward thrust bushing 42. The shunted process fluid is then released to around the canister 36 where it passes by the wetted magnets 34 and then to the shunt return 50 along the access of impeller rotation 10. The shunt inlet 48 is located outwardly on the open vane impeller 14 of the shunt return 50 located along the access of impeller rotation 10. Thus, rotation of the impeller 14 is able to drive circulation of the shunted process fluid.

(15) A rub ring 52 closes the drive end of the stuffing box inner 20 by extending inwardly to the drive 28. In addition to closing the stuffing box inner 20, the rub ring 52 is associated with a circumferential ring 54 located on the drive 28. The maximum compressive deformation in the ring 54 is less than the gap between the canister 36 and either of the magnet assemblies 32, 34. This prevents damage to the canister 36 by catastrophic failure of any of the bearings.

(16) Thus, an improved magnetically coupled centrifugal pump is shown and described. While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art that many more modifications are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims.