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Hi Michael,

Be VERY careful about doing this. If you do proceed, use Polycarbonate
and keep it thick, at least a .250 wall. Do not use acrylic. If you can
get pressure rated pipe, that would be the best. Check with a reputable
plastics supplier. There are also some types of clear PVC that are
pressure rated. I have no idea what the maximum sizes of these are. 

You might want to check with the ASME in reference to their national
pressure vessel codes for unfired pressure vessels. 

Another point: many such clear pressure vessels have a surrounding
protective perforated metal enclosure to stop parts from moving out
should a fracture occur. 

Most plastics have a pressure rating that is directly tied to operating
temperature, usually quite low. Check this carefully too.

The bottom line is: walk into this very carefully and get engineering
advice from someone with pressure vessel experience. I will check with a
colleague out here who builds food service pressure vessels and see what
he has to say.

John Bowditch

-----Original Message-----
From: Informal Science Education Network
[mailto:[log in to unmask]] On Behalf Of Michael Adams
Sent: Wednesday, July 19, 2006 10:51 AM
To: [log in to unmask]
Subject: Building up air pressure in a clear plastic pipe

ISEN-ASTC-L is a service of the Association of Science-Technology
Centers
Incorporated, a worldwide network of science museums and related
institutions.
************************************************************************
*****

At the Museum of Science in Boston we are trying to build an outreach 
demonstration for a weather program that would involve building up air 
pressure in a large clear pipe.  We would like to have 2 large diameter 
(6" or 8") pipes that are connected by a hose with valves that we could 
use to open and close so that we could vary the pressure in each 
cylinder and observe the corresponding change in temperature.  Ideally, 
we would like to have the flexibility to build up a fairly large 
pressure (about 120-150 psi) inside the cylinders.

The problem we have been having is that none of the clear plastic pipes 
that we have been looking into are suitable for air pressure because of 
the danger of the plastic exploding and sending sharp pieces 
everywhere.  This seems to be true of both clear PVC and acrylic.  Does 
anyone  know of any stronger clear plastics that we might be able to 
use that we haven't considered?  We need to use a clear material 
because we are also planning to use the tubes as a cloud formation 
chamber; students will need to be able to see inside them.  The pipes 
also need to be fairly large for visibility reasons.  This 
demonstration will be for a large scale assembly program.

Please let us know if you have any suggestions for us.

Thanks,
Mike


Michael Adams
Traveling Programs
Museum of Science
Science Park
Boston, MA 02114
(617) 589-4253
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