In my research recently, I've needed to move a very viscous fluid at a near constant flowrate. This led me to read about many different pumps and their various applications. Out of them all, my favorite happens to be the progressive cavity pump.

[caption id="" align="aligncenter" width="180"] Progressive Cavity Pump[/caption]

I think what I find most interesting about it is how simple, yet complex it is. In the simple case shown above, it is a helical screw (rotor) that is embedded in a helical cavity (stator)  with a pitch twice that of the rotor. When the rotor rotates the motion of the shaft is in the shape of a hypocycloid. In this case where the rotor is a single helix and the stator is a double helix, the hypocycloid happens to be a straight line.

I 3D printed some for testing, and I'm happy to report that the PCP pumps peanut butter like a champ. If you're interested in printing some for yourself, you can grab the STL and SolidWorks files at the link below.

Files.