SF6 is not used in an equilibrium state; there is no liquid present.
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It's been a long time since I worked around a Van de Graaf, but we used to
evacuate the pressure vessel and then fill it with SF6 gas. I forget now,
but I don't think the final pressure was much above atmospheric. It was
high enough that we could use a leak detector on the seals though. Probably
no more than 10 psi above ambient. Tank sparks were always fun when it
broke down. I think we increased the pressure a bit when running near the
max. We couldn't go too high since it increased the stress on the vacuum
We'd pump that stuff out, compress it and liquify it for storage when we
had to open the tank. That's where the high pressure values come in.
On Thu, Dec 23, 2010 at 12:39:08AM -0000, Gabriel mendez wrote:
Craig,some thing seems to be wrong with the pressure beheaviour of SF6, since is used in a several high voltage gear that not can handle the presure you mention,since they will work in extreme ambient temp..like 55?C or more!.
I will do a little more research about,in particularly with nitrogen mix , which is what I can obtain.
In other way...the metallic arms inside the probe form a shunt capacitor for a 100Moms resistor ,and add some cap to ground,obviously if we fill with silicone oil,such cap will be increased about 2,5 times....but...if we enclose the resistor/arms inside a small diameter tube filled with oil,then only this small diameter tube will contribute to an increase cap.
They will look like cylindrical concentric capacitors,the small tube with oil,inside a large one (the bodie probe),with air between.
The overal cap increasing will be less,I will try to do some numbers about.
Just an idea to work with.
--- In TekScopes@..., "Craig Sawyers" <c.sawyers@...> wrote:
Hi Craig...what I know about this SF6 is that are stable in a opencontainer and
don't evaporate at room temp.What it does in an open container tells you nothing about what it does in a
closed container. From the Air Liquide website:
"Vapor pressure (at 21 ?C or 70 ?F) : 311.83114 psi" for SF6
Which is 22 atmospheres. That is the pressure that the gas will be when in
equilibrium with a liquid in a closed container at 21C. FC114 by comparison
is 2 atmospheres at 21C.
The dielectric constant is not an issue since most gas have similarone..very
near 1.Yes, that is correct. But the pressure remains the seriously big issue.
Paul Amaranth, GCIH | Rochester MI, USA
Aurora Group, Inc. | Security, Systems & Software
paul@... | Unix & Windows