Multi-stage pump powered by integral canned motors

A multi-stage seawater pump for supplying cooling water flow to the secondary side of a steam turbine condenser system of a marine vessel, said pump comprising:

• at least two pump units each powered by a canned electric motor and connected in series in a flow path, each said pump unit including a generally hollow housing secured in said flow path, said housing having an inlet end and an outlet end, an annular stator mounted inside said housing, energizing means for supplying electrical power to said annular stator, an impeller assembly including a tubular suction shroud extending through and rotatable relative to said annular stator, an impeller secured to said tubular suction shroud, a hub positioned downstream of said impeller with respect to the water flow, and an annular rotor mounted around said tubular suction shroud and inside said annular stator, said rotor rotating said tubular suction shroud and impeller to create a pressurized water flow through said housing from said inlet end to said outlet end, said tubular suction shroud having a forward end forming a forward gap relative to said housing positioned upstream of the impeller with respect to the water flow, and an aft end forming an aft gap relative to said housing positioned downstream of the impeller with respect to the water flow, said forward gap and said aft gap being in communication with one another to form a water circulation channel between said rotor and said housing, said impeller assembly including a generally hollow shaft rotatably mounted within said hub, said shaft having an opening into the hollow thereof positioned upstream from said impeller with respect to the water flow, said tubular suction shroud having a second aft end forming a hub gap relative to said hub positioned downstream from said impeller with respect to the water flow, adjacent said outlet end of said housing, said hub gap and said opening in said shaft being in communication with one another to form a second water circulation channel between said hub and said tubular suction shroud and, said impeller assembly of each pump unit being unconnected mechanically to an impeller assembly of another of said pump units.