A Roots Blower is an air pump with strangely shaped rotors. They are used in automotive superchargers and high-vacuum pumps, among other places.

See http://en.wikipedia.org/wiki/Roots_type_supercharger

This is a stand-alone Public Domain OpenSCAD file you can use to generate these mechanisms. This is intended more as an example of an interesting mechanism than as a useful pump.

The file uses code appropriated from Leemon Baird's PublicDomainGearV1.1.scad which can be found here: http://www.thingiverse.com/thing:5505

Download and view with OpenSCAD, or try and print the STLs!

Note, the blower shown in the gif has twisted rotors, one Left and one Right. While OpenSCAD can display these, it can't render them as currently coded. The non-twisted rotor renders fine.