Luis said:
> I always wandered about clearances, how close coupled do you guys think
> is the screw to the wall of the tube?
> As anyone found any design notes on designing and building one/

Note the two variants described.

1. Screw turns in tube.

2. Tube with spiral on outer wall is turned.

[image: archimedes1.gif]

3. Spiral wound tube.

      http://www.swansea.ac.uk/grst/images/Archimedes'%20screw.jpg

Call 1 Type A.
Call 2 & 3 type B as they are essentially the same in sub-principle.

All 3 work the same way in principle BUT type B  & 3 has zero leakage and
zero clearance issues. Screws of this type could pump fluid at a variable
rate including fully stopped without loss of fluid. It would be interesting
to know how many currently in use designs use this version.

Type 3 seems potentially somewhat harder than type 1 and there are some
mechanical / drive differences but it does not seem to have a 1st order
material cost penalty. ie there may be some differences in details re
costing but at first glance it seems that a competently built version of
either would use about the same materials AND be leak free at any speed.

You could easily enough derive a material requirement formula for the 3
types.

Thought - I've never seen this done but it's sure to exist. If you had a
series of "buckets" on a rotating shaft they could have outlets arranged to
empty into a "higher bucket"on rotation. Effect would be same as an AS but
more spectacular. Extra losses would occur from pouring and impact (heating)
losses but there would be less flow losses.



    Russell McMahon
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