Re: Using SF6 for cap..

I just called to a local gas supplier and they offer SF6 in amounts of 5,
10 or 60 kg - costs 190usd, 270usd and 1300usd.. The person who gave me
those figures couldn't exactly tell how much gas there are in a bottle -
she first just told that they have 5,10 and 60 liter bottles and after a
while quoted those masses for the gas.. I did a quick calc and it appears
that 10kg is _about_ 1000l of SF6 and thus 100bar pressure in vessel which
sounds ok.. At, say, 10bar pressure in cap that amount of gas would be
good for 100liters - enough for lots of caps.. (couple liters per cap)

I'd guess that some powercompany using sf6 (and getting it in huge amounts
and low prices) will sell it at much lower price and smaller amounts..
Calculating from the figures above one rolled cap could need (max?)  30
liters of gas -> 8usd.. Quite reasonable, IMHO..

I've been thinking about the vessel the capasitor would require and
thought about using old polepig's metallic tank/vessel for the job - those
are rectangular here and generally have many (5+) millimiters thick
walls.. The vessel would need one valve, manometer and a few safety
valves.. One valve at the bottom for sucking the gas away to a storage
tank in case of failure and for filling the tank again - first suck a
vacuum and then insert sf6.. The remaining question is the safe
pressure-range the vessel should have - how big a SUDDEN raise in pressure
could be caused by a di-electric breakdown etc. - it would not be nice to
have such a metallic tank to rupture/explode.. Of course, the tank needs
to be pressure-tested first like all pressurized vessels for safety
matters but that is not a problem - propably for free/little money at
local company doing tests for fire-extinguishers IF they will test such a
beast.. :)

Comments welcome,

  Kristian Ukkonen.