This discloses a modification of the pump devices disclosed in LaRose et al.  U.S. patent application Ser.  No.  11/003,810.  The modification can also be used with other pumps as well. 
The known axial flow pumps for blood have the advantage of narrow width, when compared with radial flow pumps.  Axial flow pumps typically have a cylindrical housing with an inlet at one end, an outlet at the opposite end, and a rotor within the housing which has impeller blades attached to the rotor.  Thus, as the rotor rotates, the blades add work to the fluid, propelling the fluid through one end of the housing. 
A suspension system is provided to maintain the rotor in desired position within the housing, and a motor is provided to spin the rotor.  Blood flows between the blades, being propelled through the pump by hydrodynamic forces transferred by the blade surfaces. 
The blood then leaves the pump, flowing parallel to the axis of rotation of the rotor.  Typically in the prior art, the rotor is suspended by mechanical bearings or bushings, with a rotor shaft protruding through the pump housing to a motor drive mechanism.  Magnetic suspension is also known, as in U.S. Pat.  Nos.  6,368,083 and 5,840,070. 
Typically, axial blood flow pumps have used a thin blade design, with the motor magnets being placed either in the rotor shaft far away from the surrounding stator as in pumps by Jarvik and Incor, or they use small magnets placed within the thin blades, as in the MicroMed pump.  Both of these approaches tend to reduce the motor torque capacity and efficiency, and most use mechanical rotor support involving abutting surfaces that move relative to each other in rotation. 
In the cited application Ser.  No.  11/003,810, a new utilization of wide (thick), blade-like projections on a rotor in an axial flow configuration is provided for a blood pump, to provide a pump which is mechanically wearless, and can have improved torque.  Blood pumps, whether internally or externally located, must exhibit low hemolysis, good resistance to thrombosis, adequate system efficiency, and very high reliability for the expected duration of use for the device.  Internally located blood pumps are also subject to anatomical compability design constraints, and the need for elimination of mechanical wear and associated failure modes in order to provide successful, long-term, implantable devices.  The pump of this invention can achieve the above.  Also, the pump can be sealless. 
While such a pump of this invention is described in terms of a blood pump, it is also contemplated that the pump might be used for pumping chemically difficult fluids, where a sealless design is highly desirable, and the fluid must be gently handled for various reasons, for example because it is unstable to mechanical stress, causing decomposition and even explosiveness, or because it is another complex, biological fluid besides blood, having critical stability parameters, like blood. 
By this present invention, an improved multiple stage blood pump is provided, which gives greater pumping power, constituting a modification of a ganged series of blood pump rotors as shown in FIG.  9 of the previously cited application, with the rotors being in series.  Also, a high capacity pump of smaller diameter can be provided in this manner, which is a very significant factor in the case of an implantable pump.