OK, I think the point I didn't understand is that the shaft angle can't be so steep that the water ever "sees" a downhill path which is backwards along the screw. I don't know why it is but I have such trouble visualizing rotating things - even the photo wasn't enough for me, I had to take a paper cup and draw a spiral on it, mark some points, and then rotate it. What did it for me was to follow what happens to one "bunch" of water as it goes through. If you look at each point in time and find the local minimum of height for that bunch of water and call it point A, then when you animate the motion, point A is always moving up even though any point which you pick that is fixed to the screw has no net upward motion but only an up and then down cycle. Sean On Fri, Jul 9, 2010 at 10:42 AM, RussellMc wrote: >> When stopped, it >> doesn't take long for all liquid to drain down to the bottom pool >> elevation. The clearances I was talking of were compared to a turbine >> aircraft engine, where the blade clearances are in thousands of an inch. >> The tube does not become near total full of liquid, but maybe 1/4 full, >> and the motion of the screw is fast enough to overcome the natural flow >> of the liquid down, much like =A0a leaky bucket elevator. > > Note that the "screw binded to outer wall" version does not leak at > all when stationary. It will retain all fluid and restart immediately > where it left off when restarted (with suitable allowances for reality > such as a bit of slop and surge). > > > SUPERB EXAMPLE : > > =A0 =A0 =A0 http://www.swansea.ac.uk/grst/images/Archimedes'%20screw.jpg > > > > =A0 =A0 =A0 Russell > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist