Hi,
on a related note I keep being amazed about how many labs fill their magnets
with an essentially unknown pressure to the helium storage dewar as their
only pressure meter is the Pi-by-thumb-only overpressure meter on the dewar
(usually maxing out at the typical maximum allowed pressure of 1 bar), hence
a refill pressure of 1-1.5 psi = 70-100 mbar barely moves the needle.
Oddly, only Oxford and/or Varian supplied magnets were ever equipped with a
"proper" helium refill kit with precise helium gas flow meter to adjust refill
speed and sensitive pressure gauge (typically 3 psi max) to see what's going
on (dewar empty, filling speed too slow/fast).
Hence it is not uncommon to find people take too long for a refill which reduces
efficiency (by having a longer contact time of the barely-liquid helium inside
the transfer line). Of course too high a pressure also isn't too good (risk of
overpressure)… Different dewars may have completely different
characteristics (helium gas flow to reach a certain pressure) because of
different vessel heights, vacuum quality etc.
Cheers
Bert
> Am 30.07.2025 um 23:27 schrieb Matthias Brandl via groups.io:
>
> 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/
>
>
Magnetic resonance equipment, service, training & more
Selling & buying used NMR equipment (all vendors)
Dr. rer. nat. Bert Heise
Owner, Applications Scientist
Spin-Doc Bert Heise
Kiefernweg 13
58239 Schwerte
Germany
Mobile: +49 171 5135315
Email: bert.heise_at_spin-doc.net
Web: http://www.spin-doc.net
Representing:
Stelar Fast Field Cycling NMR Relaxometers (
http://www.stelar.it)
MestreLab NMR Software (
http://www.mestrelab.com)
Barthel HF Amplifiers (
http://www.barthel-hf.de)
-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#2638): https://urldefense.com/v3/__https://ammrl.groups=
.io/g/main/message/2638__;!!PvDODwlR4mBZyAb0!UFGxqmAm7_LgZ5E5pOHHNLy91Xp1Dg=
Y9N3khGacW65F9IqHnVxzOTm-EPnB65h_um3JC8MLpkmrp1sAQ4bRguw$
Mute This Topic: https://urldefense.com/v3/__https://groups.io/mt/114451451=
/7559972__;!!PvDODwlR4mBZyAb0!UFGxqmAm7_LgZ5E5pOHHNLy91Xp1DgY9N3khGacW65F9I=
qHnVxzOTm-EPnB65h_um3JC8MLpkmrp1sAI9XmzWw$
Mute #poll-notice:
https://urldefense.com/v3/__https://ammrl.groups.io/g/mai=
n/mutehashtag/poll-notice__;!!PvDODwlR4mBZyAb0!UFGxqmAm7_LgZ5E5pOHHNLy91Xp1=
DgY9N3khGacW65F9IqHnVxzOTm-EPnB65h_um3JC8MLpkmrp1sDfM54tTg$
Group Owner: main+owner_at_ammrl.groups.io
Unsubscribe: https://urldefense.com/v3/__https://ammrl.groups.io/g/main/lea=
ve/12177410/7559972/1125599165/xyzzy__;!!PvDODwlR4mBZyAb0!UFGxqmAm7_LgZ5E5p=
OHHNLy91Xp1DgY9N3khGacW65F9IqHnVxzOTm-EPnB65h_um3JC8MLpkmrp1sAok_eE2Q$ [wa=
lt_at_hawaii.edu]
-=-=-=-=-=-=-=-=-=-=-=-
Received on Thu Jul 31 2025 - 10:26:33 MST