ISEN-ASTC-L is a service of the Association of Science-Technology Centers Incorporated, a worldwide network of science museums and related institutions. ***************************************************************************** Or use hemispherical heads. We used stainless heads with O-ring gaskets and bolts. It worked just fine. Your warning is not to be ignored, however. John B -----Original Message----- From: Informal Science Education Network [mailto:[log in to unmask]] On Behalf Of Albert J. Read Sent: Monday, October 23, 2006 1:16 PM To: [log in to unmask] Subject: Re: Clear cylinders and pulling a vacuum. ISEN-ASTC-L is a service of the Association of Science-Technology Centers Incorporated, a worldwide network of science museums and related institutions. ************************************************************************ ***** A word of caution: since atmospheric pressure, about 15 pounds per square inch in customary units, translates into about one ton per square foot, a designer of any chamber being evacuated should be aware of the strength needed, especially when large-sized chambers are to be evacuated. The tube being discussed, about 30 cm (or one foot) diameter, would presumably have flat end caps which would be subjected to an inward force of about 0.8 ton if there is vacuum inside and normal atmospheric pressure outside. Recall the heavy, thick glass front faces of older television picture tubes, needed for strength to prevent implosion. Albert J. Read Director Emeritus, Science Discovery Center of Oneonta State University of New York, College at Oneonta -----Original Message----- From: Informal Science Education Network on behalf of Ian Russell Sent: Mon 10/23/2006 9:00 AM To: [log in to unmask] Subject: Re: Clear cylinders and pulling a vacuum. ISEN-ASTC-L is a service of the Association of Science-Technology Centers Incorporated, a worldwide network of science museums and related institutions. ************************************************************************ ***** Here in the UK it is possible to buy long Perspex (=Plexiglass) tubes with 30cm diameter. I have successfully produced a high-vacuum exhibit using this material. Mine used only a short length of ~30cm tube, but a longer length should be equally resistant to external pressure. Be careful to avoid bending forces though. Even with thick walls, it is possible to see inside with perfect clarity because this material is very precisely formed and highly transparent. There's a photo of my version here (scroll down to "Silence of space") http://www.interactives.co.uk/hands_rumbo.htm [log in to unmask] * http://www.interactives.co.uk * Give people facts and you feed their minds for an hour. Awaken curiosity and they feed their own minds for a lifetime. * Ian Russell *********************************************************************** More information about the Informal Science Education Network and the Association of Science-Technology Centers may be found at http://www.astc.org. To remove your e-mail address from the ISEN-ASTC-L list, send the message SIGNOFF ISEN-ASTC-L in the BODY of a message to [log in to unmask] *********************************************************************** More information about the Informal Science Education Network and the Association of Science-Technology Centers may be found at http://www.astc.org. To remove your e-mail address from the ISEN-ASTC-L list, send the message SIGNOFF ISEN-ASTC-L in the BODY of a message to [log in to unmask] *********************************************************************** More information about the Informal Science Education Network and the Association of Science-Technology Centers may be found at http://www.astc.org. To remove your e-mail address from the ISEN-ASTC-L list, send the message SIGNOFF ISEN-ASTC-L in the BODY of a message to [log in to unmask]