Hello,
Despite the closed loop and no bag- we also have a QT system- the pumped magnet
pressure during a fill is directly correlated to the atmospheric pressure. I
don't know if having an APD related to the pressure control for the pumped
magnet is what affects that (Sameer?).
I've never calculated it out, but have always felt that after a few days of
higher or lower than usual atmospheric pressure there is a small difference
in liquid levels. We recover around 90% and assume that we are still losing
around the old flowmeters on the oxford/varian magnets that we've never
removed- so I guess the system isn't 100% closed...
Tara
*********************************************
Tara Sprules
0.6 FTE, Working days: Monday, Wednesday and Thursday
QANUC
Quebec/Eastern Canada High Field NMR Facility
http://www.nmrlab.mcgill.ca
phone: (514) 398-1721
fax: (514) 398-8254
3420 University St., Rm 023
McGill University
Montreal, QC, H3A 2A7
SHIPPING ADDRESS:
Department of Chemistry, McGill University
Rm. 41 801 Sherbrooke St. W
Montreal QC
H3A 0B8
*********************************************
From: main_at_ammrl.groups.io on behalf of Sameer Al-Abdul-Wahid via groups.io
> Date: Friday, February 6, 2026 at 7:42 AM
> To: main_at_ammrl.groups.io
> Subject: Re: [AMMRL] Helium Boil Off Question
Hi Luke,
We have a Quantum Technologies HRS with medium‑pressure storage tanks.
I’d describe our system as almost closed-loop, since the recovery
header pressure is held at ~0.2 psi above atmospheric via a regulator which
effectively “senses” atmospheric pressure.
When we first brought the system online, we noticed that the amount of passive
boil‑off we collected varied slightly from day to day. After adding an
atmospheric pressure sensor to our monitoring setup, we saw a pattern: on days
when atmospheric pressure is rising, we collect less helium; when it’s
falling, we collect more. For us, the day‑to‑day swing is under
±10% even when the weather brings big pressure changes.
Best,
Sameer
--
Sameer Al-Abdul-Wahid, Ph.D.
Manager, Nuclear Magnetic Resonance Centre <
http://nmr.uoguelph.ca/>
University of Guelph
519-824-4120 x58914 / s.wahid_at_uoguelph.ca
> From: main_at_ammrl.groups.io on behalf of Michael Groves via groups.io
> Date: Thursday, February 5, 2026 at 19:08
> To: main_at_ammrl.groups.io
> Subject: Re: [AMMRL] Helium Boil Off Question
Hi Luke,
"Maintaining accumulated volume but failing to liquefy any additional gas"
So the level of liquid in the magnets is dropping but the level in the storage
dewar stays the same? You sure you don't have a leak somewhere? Unless it
was all somehow getting shoved into the MPTs and just sitting there.
I would also expect an instrument with that kind of liquefier to be pretty
insensitive to air pressure changes, but if there was a leak then that would
provide a mechanism for the ambient pressure to affect the boiloff rate.
Anyway, that's my $0.02. Worth more or less depending on the local exchange
rate...
Cheers,
Mike
On Thursday, February 5, 2026 at 02:24:21 PM MST, Fulton, Luke via groups.io wrote:
Hi spinlanders,
We (hopefully) finished troubleshooting an issue with our helium recovery
system this week. It was maintaining the accumulated volume but failing to
liquify any additional gas into the production dewar. Turned out the automated
threshold settings were out of sync with our magnet's boil off rates. During
our communications with the manufacturer a curious question came up.
The HRS design is a closed loop. We have medium pressure storage tanks rather
than a gas collection bag, and it's an all-in-one system. Gas is pulled directly
from the header into a purifier, and from there goes to the liquefier. Under
high exhaust conditions, such as a helium fill, the gas is temporarily redirected
towards the MPT's, and purified/liquefied later. We discussed variable boil off
rates due to weather patterns, and the manufacturer suggests that under this
system the magnet boiloff should be agnostic to atmospheric changes.
Now I can empirically attest that my magnets are still an effective weather-wise.
And it has me pondering, why? Perhaps the manufacturer was mistaken on this detail.
Or, perhaps it's a clue that something else still requires my attention. My
instincts lean towards the former, but I've learned to check the alternative just
in case. Anyone have an opinion they'd be willing to share?
Kind regards,
Luke
Luke Fulton, PhD
CHEM BLDG R003
NMR Core Facility Director
Unit 3060
COR2E & Department of Chemistry
55 N Eagleville Road
University of Connecticut
Storrs, CT 06279
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Received on Fri Feb 06 2026 - 06:13:06 MST