if the bottom of the pipe has "lips" like that i bet that you don't even need the screw inside to push the stuff up... the screw only eases the process but what pushes the stuff up is the lips that are shoving stuff inside the pipe... its not at all counter-intuitive...,(reply>), @IamIUareU Its quite mind bending. like all good topics from Tom!,(reply>), @Gordon Richardson i just wanted to point on the false claim that Tom did "the screw pushes the grains up" which is not true, the lips are pushing stuff up and as you said the screw only holds the grains not to fall back down and to make the device able to be made in long heights...,(reply>), @Gordon Richardson the push force of the pipe without a screw depends on the spinning speed of the pipe... as i said the screw eases the process so yes you are right...,(reply>), The lips only help get the particles into the tube. If the column is too high, the weight of gravity would stop it pushing any higher. With a rotating force relative to the screw, there is no height limit.