Conventional multi-stage centrifugal pumps provide a plurality of impellers on the same shaft, and produce a high pressure head. Sealing, supporting and guiding the shaft (with bearings), and the balancing of axial forces at the non-driven end of such pumps, are typically complicated procedures. REDUCING VALVESFor example in some conventional constructions the non-driven end of the shaft is mounted by a pair of tapered roller bearings which are spaced a significant distance from the pump itself since sealing of the pump is carried out by a conventional packing (which is relatively long). Since the packing must be occasionally replaced, it must be possible to remove the packing.Forged Steel Valves A balancing drum is preferably also provided between the packing and the last impeller on the shaft, for balancing a majority of the axial forces generated by the pump. Centrifugal pumps always generate an axial force causing the impellers to move toward the suction channel. The balancing drum typically has a labyrinth seal, and between the cylindrical surfaces of the balancing drum there is a gap of about 0.05 mm. The pressure generated by the pump is introduced into the cavity between the last impeller and the balancing drum so that the pressure of the pump against the balancing drum tends to push the balancing drum further away from the impeller.Instrument Manifolds The force that is thus generated is counter-directional to the axial force generated by pumping so that the axial force loading the bearings of the pump is the difference between the axial forces having different directions.

In most conventional multi-stage centrifugal pumps the length of the actual pump (shaft and impellers) is only about 55% of the total length of the apparatus. A substantial portion of the length of the entire assembly is due to the spaced location of the bearings at the non-driven end as a result of the packing construction. This requires a sturdier and longer shaft than is desired, the sturdier construction being necessary to resist the bending load on the shaft because of its length.

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2012-01-10

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