On Thu, 16 Oct 2008 21:53:20 -0700, Jeff Liebermann
wrote:

Plug up the other end with whatever is handy. Blow
air into the center of the tube. Run your fingers around the edges of
the tube and note which way the air is flowing. That's what will
happen if the compressed air is not sufficient to blow 30 lbs of sand
into the air. The air and the sand will flow back into the pipe in
the opposite direction as the compressed air.

Hi Jeff,

Well, it's been a coon's age since I've seen vacuum cleaners that
would let me attach to their exhaust - so that's out.

As for driving compressed air into a short (or open). I've done that,
but not for sand excavation. Rather, I've used what was commercially
called the "vortex effect" which separates the two air current flows
you allude to above to create a hot stream and a chilled stream of
air. (Elevated or depressed from the average of the inlet
temperature.) I used this for cooling electronics in a paper mill.
Not particularly efficient, but compressed air was available, and the
VorTec nozzle was a quick and easy solution to their NEMA enclosures.

See:
http://www.vortec.com/support_casestudies.php
or
https://secure.vortec.com/store_prod...tID=9&prodID=6

This, and some of my fluidic applications constitute a specialized
niche in alternative logic systems. Notably, they all work off
principles of reflected power that demonstrate palpable examples.

73's
Richard Clark, KB7QHC