On Fri, Nov 3, 2017 at 5:16 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 ...
>
>
> Hi. Removing occluded gases off the internal surfaces is not so simple.
> Heating and several purges maybe required to get rid of the last molecule=
s
> of oxygen/ water vapor off the surfaces. Vacuum tube manufacturing in day=
s
> of old required various techniques to eliminate occluded contaminants whi=
ch
> would 'poison' the Cathode coating on the emission surface. Reactive
> metals, magnesium was used as a getter to mop up the remains of the oxyge=
n
> out gassing during life of the tube . As an aside, the leak rate on the
> glass to metal pressed seal was absolutely leakproof using lower melting
> point uranium glass, now dumet wires with similar thermal characteristics
> are use.

On the subject of gas metering, we used a simple arraignment of two low
volume capacity solenoid valves with a short connection pipe in series to
sequentially pulse measured slugs of gas into a superplastic structure to
inflate at a precise rate and shape. The volumes transferred were quite
small and allowed the superplastic forming rate to be carefully controlled.
Was a YouTube a while back showing French engineer making his own trI ode
tubes




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