Are there any materials/mechanical fixings, seals, o-rings that are impermeable to helium?
I have been asked to design an enclosure for a projector that will be in a hyperbaric decompression chamber for prolonged periods of time. One of the design specifications is that it should be ‘helium-proof’
Just looking for some information on anything ‘helium proof’ such as materials, fixings etc etc as the world wide web seems to be lacking an awful lot of infomation on the subject.
Thanks in advance and regards
O rings are notoriously permeable to helium. You can use gold wire seals (between two flat flanges), "Conflat" copper seals, or indium wire seals (but these are a bit fragile). For electrical feed thrus, only vacuum brazed ceramic feedthrus or Kovar in glass will work (available from Varian). For mechanical feedthrus, use brass or stainless bellows. These are also available from Varian at a price.
January 15th, 2010 at 9:39 pm
helium, like other gasses, seep through most materials at very slow rates. to find an O-ring or sealant for helium i would start with helium tank suppliers, or items used on the shuttle to contain Hydrogen. typical metals will work to a point and sillicates will seal, but the real question is HOW helium proof does it need to be? (in liters per hour per square foot of exposed surface)
References :
January 15th, 2010 at 9:45 pm
O rings are notoriously permeable to helium. You can use gold wire seals (between two flat flanges), "Conflat" copper seals, or indium wire seals (but these are a bit fragile). For electrical feed thrus, only vacuum brazed ceramic feedthrus or Kovar in glass will work (available from Varian). For mechanical feedthrus, use brass or stainless bellows. These are also available from Varian at a price.
References :
I have worked on Ultra High Vacuum systems, and leak detection is done using helium so all seals must be completely helium proof.