The idea of using a vacuum to thresh millet sucks.

We made a feeble attempt at testing this idea, using an old discarded vacuum cleaner, fitted with a narrow bore (~5mm) hose. The vacuum cleaner produced little suction at low flow rates -- it could not "concentrate" the air flow through a ~1.5" hose into a small one, and the large hose produced inadequate suction or turbulence to affect the millet.

Theoretically, a vacuum can get no lower pressure than zero, so it can create at most a 1 atmosphere pressure gradient, whereas an air compressor can create in principle an arbitrary large pressure gradient. Therefore a compressor would be a more viable approach than a vacuum for using the force of air to dislodge millet grain. But air is so light it will require tremendous speed to deliver an inpulse of momentum to the millet grain, compared to a wire. Achieving such air flows from human power seems unlikely, and therefore we are not pursuing forced air methods for dislodging seed from floret.


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