Helium valve seal 1

[doccouch]

Problem: I need to seal and then open quickly a 30 inch orfice. It is to hold 0.18 psi helium at -45 deg C with minimal leaks. My best sealing material I beleive is silicone. How could the valve best seal helium? a flat gasket design? o-ring design? other?

 

[btrueblood]

Why do you think silicone is your best sealing material? Silicone rubber is very permeable to gas/vapor. Butyl rubber is a much less permeable sealing material.

 

[gerhardl]

looking theoretically at your problem (no further details than given - especially on opening/closing mechanism) the best sealing material could be butyl rubber as stated above.

Best sealing constructions for flanges or lid-like sealings would probably be o-ring in groove engineered to fit together (dept and width of groove to give just enough room for the O-ring to compress and fill grove at given conditions - (this is an art) - counterface flat).

If you really want to put money into quality the O-ring would be of PTFE to cover (more than required) of the lower temperature range or FEP - construction (rubber covered by PTFE).

Note: a lot of cheaper solutions exists, both for form and material just check what is reasonable result and cost for you.

Ask a top quality sealing producer/supplier!