The analysis fo this machine is largely wrong. The pumping action is generated by the entry part of the tube. The rotation of the tube is adding very little force to the material at least greatly reducing friction between tube and material. The reason its not generating dust is because the pumping action is only at the beginning and the upper material is lifted by the following material underneath. It looks the same but the pumping is really generated by a different principle than a rotating screw. And thats why we all are confused.