Magnetically coupled sealless centrifugal pump
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.
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.