Pumps – Motor driven – Electric or magnetic motor
Reexamination Certificate
1999-10-28
2001-09-25
Walberg, Teresa (Department: 3742)
Pumps
Motor driven
Electric or magnetic motor
C415S122100
Reexamination Certificate
active
06293772
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a containment member for confining fluid to a wet-end of a magnetic-drive centrifugal pump.
BACKGROUND
Magnetic-drive centrifugal pumps are well suited for pumping caustic and hazardous fluids because shaft seals are not required. Instead of shaft seals, magnetic-drive pumps generally feature a pump shaft separated from a drive shaft by a containment shell. The drive shaft is arranged to rotate with a first magnetic assembly, which is magnetically coupled to a second magnetic assembly. The second magnetic assembly applies torque to the pump shaft to pump a fluid contained within the containment shell.
The reliability of containment shells may be rated in terms a burst strength. The burst strength is a pressure per unit area from the pumped fluid on the containment shell that results in damage to the containment shell sufficient to cause the leakage of fluid from the containment shell. In general, the higher burst strength, the better the containment shell. However, increasing the burst strength of a containment shell poses some difficult technical obstacles. For example, increasing the thickness of the containment shell or adding metallic reinforcement to the containment shell may significantly degrade pump performance, making any increase in the strength of the containment shell irrelevant. If the thickness of the containment shell is too great or if metal reinforcements are used indiscriminately, magnetic coupling between the first magnetic assembly and the second magnetic assembly may be impaired. In turn, the impeller may stop rotating entirely or may rotate too slowly for proper pump performance. Thus, a need exists for a containment shell with a superior burst strength, without sacrificing the requisite efficiency of the magnetic coupling between the first magnetic assembly and the second magnetic assembly.
Many magnetically driven pumps include a front support and a rear support to support a rotating or a stationary pump shaft. The front support is often located such that the front support obstructs the inlet flow to the impeller, detrimentally limiting the performance of the pump under conditions of low net positive suction head (NPSH). Meanwhile, the rear support may be integral with a containment shell of polymer composite construction. The containment shell of the dual-support pump is often structurally inadequate to support a shaft without the assistance of a front support. Consequently, elimination of a front support for low net NPSH applications may reduce the burst strength of the containment shell, provide inadequate radial support for the pump shaft, or otherwise detrimentally impact pump reliability. Thus, a need exists for a containment shell that can support radial loads from a cantilevered shaft, while meeting a burst strength design goal.
SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of the invention, a containment member for a magnetic-drive centrifugal pump includes a reinforcement member cooperating with an inner layer and an outer layer to form a unitary body. The inner layer has a first side defining a generally annular recess and a second side opposite the first side. The second side defines a pocket located coaxially and radially inward with respect to the annular recess. The reinforcement member has a stem portion nested within the pocket. The reinforcement member has a curved portion extending radially outward from the stem portion. The stem portion has a first radial dimension and the curved portion has a second radial dimension greater than the first radial dimension. The outer layer covers the curved portion and is affixed to the curved portion and the inner layer.
The containment member is well-suited for supporting a cantilevered shaft because during operation of a pump the stem portion accepts a radial load from the shaft, the stem portion transfers the radial load to the curved portion, and the curved portion distributes the radial load to the inner layer, the outer layer, or both. The curved portion may predominately distribute the radial load over adjoining surface areas defined between the first radial dimension and the second radial dimension. The resultant distribution of stress on and within the adjoining areas is compatible with the longevity and reliable service of a polymer-based construction for the inner layer and the outer layer. A polymer-based construction refers, for example, to a polymer matrix reinforced by reinforcing material distributed within the polymer matrix.
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Robert Neumaier,Hermetic Pumps, Gulf Publishing, Houston, Texas, pp. 154-155; 356-359.
Brown Jeffrey S.
Klein Manfred P.
McAloon Scott A.
Phelps Peter E.
Innovative Mag-Drive, LLC
Van Quang
Walberg Teresa
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