Hi Ken & Others
I would be interested in knowing what constitutes "good" *vs* "bad"
vacuum. Maybe people who pump down their lines would consider sharing
their vacuum measurements, if available, and maybe a service engineer could
comment on what kind of vacuum is expected for a new and presumably "good"
line.
For my part, I usually get between 2.4 and 2.9 x 10^-3 mbar.
In a conversation with a service engineer recently, evidence of softness
was the transfer line being cold to the touch during a fill. In a
conversation with a different service engineer many years ago, he advised
not pumping down the line unless there was evidence of softness.
Kind regards,
Craig.
On Wed, 30 Jul 2025 at 23:34, Matthias Brandl via groups.io wrote:
> Hi Ken,
>
> What exactly do you/the engineer consider "evidence of it having gone
> soft"? I could imagine any one of the following, but the sensitivity
> between them would vary widely:
>
> - Noticeable increase in transfer losses (with or without looking
> specifically)
> - Increased fill duration (due to the higher back pressure from the
> evaporation in the line)
> - Line getting cold/frosting during line cool-down (vacuum contamination
> with "condensibles")
> - Increased condensation on the line also during the fill (vacuum
> contamination with helium, possibly due to cracks/pinholes)
> - Decreased surface temperature of the line on the narrow parts (this is
> probably the most sensitive, but also the least obvious)
>
> Best,
> Matthias
>
>
> On 30/07/2025 18:26, Kenneth Sharp-Knott via groups.io wrote:
> > Just to follow-up... The reason I ask is the engineer mentioned that
> > most people wait far too long. By the time you see evidence of it
> > having gone soft, you have likely been losing quite a bit of helium due
> > to excessive boiloff for some time.
> > Apparently most transfer lines also come with the necessary equipment to
> > pump it down. They were some of the bit and pieces lying around the lab
> > that I had no idea of the purpose.
> >
>
> --
> Dr. rer. nat. Matthias Brandl (he/him or they/them)
>
> Technical University of Munich
> TUM School of Natural Sciences - BNMRZ
> Chair of Biomolecular NMR Spectroscopy (Prof. Sattler)
>
> Lichtenbergstr. 4 (postal)
> Ernst-Otto-Fischer-Str. 2 (physical)
> 85748 Garching b. Muenchen
>
> Phone +49 89 289-52617
>
> matthias.brandl_at_tum.de
> https://www.sattlerlab.de/
> https://www.bnmrz.org/
>
>
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Received on Thu Jul 31 2025 - 10:25:52 MST