[Eclipze]

Oh very nice! How did you make the auger? Need some more pictures/details of how you have accomplished the mechanism please

[scsi]

The auger you can see on the desk next to the pump head. Took my Dremel and hacked the stepper motor shaft so that it resembles a flat screwdriver. Drilled couple of holes in a piece of HDPE and put some fittings here and there. Next time I will get proper luer fittings and machine the piece on my mill out of Delrin so it wont look so ugly.
The uC in the background is driving stepper by issuing step/direction commands following a simple program. Speed and pullback is adjustable via trimpots that uC is reading. Stepper driver is from Pololu. They also make cheap mylar stencils for $25+ http://www.pololu.com/catalog/product/1202

[Eclipze]

Drilled couple of holes in a piece of HDPE and put some fittings here and there.

Hahaaa... now your teasing without enough details

[scsi]

Literally, just two holes in a piece of HDPE not counting mounting holes. This was an ugly attempt of making something similar to the proper auger valve like Techcon ones on the picture attached. They have molded in luer fittings, which is nice. Techcon sells these Disposable Material Path valve assemblies in bags of 10 for something close to $500. Hence the attempt to make my own. It's not as easily disposable, but costs just a couple cents. The hardest part was to match the hole size of the screw well to the screw OD. I ended up making the hole slightly smaller and then used the screw itself to make it larger. Again, the screw that I'm using is the one you can see on the picture.

And another illustration - meat grinder that uses the same principle of operation. Some pressure is necessary on the inlet for the thing to work properly. Something like 5-10 PSI air is all it needs.

-scsi