A primary feature of the invention is to provide a centrifugal pump having a casing with a shrouded impeller located within an impeller cavity opening to a volute entrance and having pumping means communicating with a substantially sealed space behind the inner portion of the rear shroud for pumping fluid from the space to the volute entrance. This avoids the delivery of hot fluid to a low pressure inlet area. More particularly, a pair of labyrinth seals are associated with the front and rear shrouds of the impeller and with leakage past the labyrinth seal associated with the rear shroud flowing to the sealed space behind the innermost portion of the rear shroud.Balance Valves A shrouded secondary pump integral with the rear shroud of the impeller pumps the fluid from the space to the volute entrance. The space is sealed by a rotary shaft seal which precludes high temperature thrust and journal bearing lubrication flows entering the space and being delivered to pump discharge.Needle Valves This aids in holding down the temperature of front labyrinth seal leakage to a low pressure inlet area.

Another feature of the invention is the use of a planar thrust bearing adjacent an end of the impeller shaft for the impeller of a centrifugal pump which coacts with the planar portion of a journal bearng and with lubrication provided by fuel returning to the centrifugal pump. MUD VALVESFront and rear labyrinth seals associated with the shrouds of the impeller are located at different distances from the axis of rotation of the impeller shaft to provide a pressure force giving a minimal forward thrust to urge the thrust bearing towards the journal bearing and control bearing leakage which flows to a low pressure area at the inlet of an inducer section of the centrifugal pump.

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2012-01-18

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