I've always fancied attempting to get a lobe pump made up via plastic injection molding for the lobes. One could even use the same mold for both lobe rotors, and even after accounting for the draft required for the mold to eject, if they face opposite ways they will still line up just fine.
No need for the lobes to actually touch. They can clear each other by around 0.2mm or so. For a quad-lobe design, where each rotor is about 4cm in diameter x 2cm deep, giving a total external pumping chamber dimensions of around 9cm x 5cm, or no bigger than many centrifugal pumps, affix a shaft and same sized gears at each end of the rotor to ensure that they keep in sync, and do a standard mag-drive on one of the rotors to drive the pump, and you can have a relatively cheap to make high-pressure medium-flow pump.
Each revolution displaces about 7.5cc's. At a lazy (and quiet) 2000RPM, the pump would be pushing around 15LPM/4GPM. The clearances can be toyed with to balance the mag-drive's torque with flow "seepage" through the clearances to provide a correct balance with fluids of the viscosity of 0C cold water without causing the mag-drive to "slip". Aim it all to work for around a 25PSI peak pressure head at zero flow so people's heater-cores aren't put in danger.
Since it's a hobby pump, the pump mechanism casing would have to be cast in clear polycarbonate.
Oh well, I can dream!
