Hmm, I wasn't aware that balloons used lower grade helium (in fact, based
on a quick Google search, it seems like they usually use the same grade as
is used for welding shielding gas, which is grade 5 (99.999%))

I don't think there is an inexpensive source of Krypton or Xenon. The
source for those gasses is the same as argon (fractional distillation of
ordinary air) and the abundance of Kr and Xe in air is extremely small,
whereas Ar is almost 1%.

I bought an aluminum 2200psi, I think 40 cubic foot (at STP) cylinder of
ultra-pure Argon for about $130 at my local welding supply two years ago. I
still have half of it. Most of that cost was the cylinder and valve. I
think a refill would be about $40. I had to purchase a regulator
separately. It is eventually going to be used to seal alkali metals
(sodium, potassium) in ampoules under inert gas. So far the only thing I
have done with it, which ended up using about half of the tank, was to do
an experiment to measure the density of Argon (I got a result which was
only a few percent off of the textbook value). It was good practice using
the flow-rate regulator, too.

Even if you don't need pressure I would think that standard high pressure
tanks would be the most cost effective for you because of the quantity they
can hold in a compact space. I chose to buy the tank but you can also rent
them for much less.

Sean


On Fri, Nov 3, 2017 at 12:13 PM, Van Horn, David <
david.vanhorn@backcountryaccess.com> wrote:

> I have local sources for helium balloons that use actual helium, not
> "balloon gas" so I pay about $1 for 2 or so liters of gas in a convenient
> disposable container.
> I don't need pressure, I'm always pulling the gas anyway.
> My Neon and Argon come in glass flasks for $70/2l
> Still working on a cost effective source for Xenon.
>
> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
> Of Sean Breheny
> Sent: Friday, November 3, 2017 10:02 AM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Vacuum plumbing
>
> Is there any reason you don't use argon as your rinse gas? It's much
> cheaper.
>
> On Fri, Nov 3, 2017 at 11:15 AM, Van Horn, David < david.vanhorn@
> backcountryaccess.com> wrote:
>
> > Fortunately my only use for helium is as a rinse gas.  Vac the system,
> > fill with He, then vac it again, and call it clean.  :)
> >
> > -----Original Message-----
> > From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
> > Behalf Of alan.b.pearce@stfc.ac.uk
> > Sent: Friday, November 3, 2017 3:30 AM
> > To: piclist@mit.edu
> > Subject: RE: [EE] Vacuum plumbing
> >
> > > I still wish I could find a book/document/etc that describes the
> > > building of a vacuum system for the range of 1 torr to 10 microns or
> so.
> > > Seems to be a black art.
> >
> > Judging by the difficulties a program I am working on is having
> > sealing helium over a temperature range, it is very much a black art.
> >
> > Thankfully I'm only involved in the electricals ...
> >
> >
> >
> > --
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