NASA formerly used Viton brand fluorocarbon o-ring with a rather high Tg. Mistake. The Tg is too high, and these become hard on cooling below -5C.<br /><br />NASA should have used Kalrez fluorocarbon o-rings (made by DuPont), which were commercially available at that time. Kalrez has a Tg of about -40C, so it would have stayed flexible even on a cold day. Also Kalrez is stable to 325C (much higher), and has excellent hot plasma resistance. Kalrez is quite expensive, whereas Viton is much cheaper.<br /><br />I recall reading an article in C&E News when NASA first chose to use Viton o-rings, and thinking this was not the best choice. I was just a lowly grad student at the time.<br /><br />I don't know what brand of o-rings were used after the joint was redesigned, and have alway wondered. Any idea? <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>