Hi all,
We have a QT all metal HRS and have back pressure regulators (BPRs) on most
of our magnets (only one has an APD, which supposedly sets an absolute pressure
untethered to atmospheric). For the magnets with BPRs, we see the flow on the
ball flowmeter go up when rain is not the way and stay lower when the forecast
is sunny, like we used to before the HRS came along. Perhaps it makes sense
that the BPR, which is setting pressure in the magnet helium vessel relative
to atmospheric pressure, is introducing the influence of atmospheric pressure
into our system.
Margaret
> From: main_at_ammrl.groups.io on behalf of Fulton, Luke via groups.io
> Date: Friday, February 6, 2026 at 10:17 AM
> To: main_at_ammrl.groups.io <main_at_ammrl.groups.io>
> Subject: Re: [AMMRL] Helium Boil Off Question
Hi all,
Thanks for the feedback!
Looks like there's a general consensus that for a closed loop recovery system
the magnet boil off rates should *not* be affected by atmospheric conditions.
In practice, multiple folks have observed the opposite to varying degrees. So
the question turns towards whether the HRS design is truly closed loop, or if
there are compromised part(s) which reopen the loop to atmospheric sensitivity.
Leaks are notoriously difficult to eliminate making it tough to know either way.
A few clarifications about our HRS setup here:
-Boil off rate observations are based on flow meters. They're located upstream
of the one-way check valve, and are connected with clear flexible rubber hosing.
-The HRS has several PRV's scatted throughout its major sections. These are
referenced to atmospheric pressure, but only open for <1 second under rare and
specific circumstances.
-The mobile transport dewar is connected to the header. The transfer is kept
inserted at both ends into both production and transport dewars, at manufacturer
recommendation. We do not transfer frequently enough to keep the transport dewar
consistently cold. I haven't determined yet whether or not it's optimal to stay
connected after it fully warms.
-Until just recently our Liquefier was stuck in Idle mode. The cold head was still
running and maintaining our previously collected liquid within the production dewar.
Additional boil off from the magnets could not be liquified and was lost to atmosphere.
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
________________________________
> From: main_at_ammrl.groups.io on behalf of Tara Sprules via groups.io
> Sent: Friday, February 6, 2026 9:06 AM
> To: main_at_ammrl.groups.io <main_at_ammrl.groups.io>
> Subject: Re: [AMMRL] Helium Boil Off Question
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
-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#3194): https://urldefense.com/v3/__https://ammrl.groups=
.io/g/main/message/3194__;!!PvDODwlR4mBZyAb0!TnYnYvFaTPzUgkzmlIseYCB1UAfXhQ=
yxkb0bLbZTKtAftcFFB1Bc1YOio-1Mll6T1zrsKXCrx40u1Q19iwZQp9eE0I4F$
Mute This Topic: https://urldefense.com/v3/__https://groups.io/mt/117661513=
/7559972__;!!PvDODwlR4mBZyAb0!TnYnYvFaTPzUgkzmlIseYCB1UAfXhQyxkb0bLbZTKtAft=
cFFB1Bc1YOio-1Mll6T1zrsKXCrx40u1Q19iwZQp5BokJzc$
Group Owner: main+owner_at_ammrl.groups.io
-=-=-=-=-=-=-=-=-=-=-=-
Received on Fri Feb 06 2026 - 08:36:17 MST