3D printed pump designs

Hey!

One thing I'm interested in printing is pumps. There are a lot of pump designs on Thingiverse (http://www.thingiverse.com/search/page:1?q=pump&sa=) for different kinds of pumps: centrifugal, peristaltic, progressive cavity, piston, etc. For some of these designs, I expect getting tight enough tolerances would be an issue. I tried designing a peristaltic pump. The print quality was probably the best of anything I've printed so far, but it didn't work as a pump, largely due to the tolerance issue.
Has anyone else tried printing pumps with any success? Know of any proven designs on Thingiverse or elsewhere?