Dear Ulli,
We are using an old Pfeiffer-Balzers turbo pump that can easily reach
10^-6 mbar at the pump inlet. Whatever is left of this once inside the
transfer line/dewar is another story (my guess would be at least one
decade worse)...
Best,
Matthias
On 31/07/2025 15:35, Ulrike Werner-Zwanziger via groups.io wrote:
> Dear all,
>
> Thanks for this discussion. What kind of pumps do you use?
>
> Happy resonating,
> Ulli
>
> On Wed, Jul 30, 2025 at 6:34 PM Matthias Brandl via groups.io <http://
> groups.io> <matthias.brandl=tum.de_at_groups.io <mailto:tum.de_at_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 <http://
> 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 <mailto:matthias.brandl_at_tum.de>
> https://www.sattlerlab.de/ <https://www.sattlerlab.de/>
> https://www.bnmrz.org/ <https://www.bnmrz.org/>
>
>
>
>
>
>
>
>
> --
> Dr. Ulrike Werner-Zwanziger
> Adjunct Professor
> Department of Chemistry, NMR-3,
> Dalhousie University
> 6245 Castine Way (!!!new address!!!)
> PO BOX 15000
> Halifax, NS B3H 4R2
>
> e-mail: Ulli.Zwanziger_at_Dal.ca
> Tel. 1 902 494 8085
> FAX: 1 902 494 1310
>
>
--
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 Mon Aug 04 2025 - 03:59:33 MST