Hi, Matthias
Thanks for your suggestions.
The helium boil off rate increased 10% after this change. I tried to isolate
the vacuum line with the shut off valve. It looks like the pressure reading
is the same. The temperature of magnet is stable as I mentioned the fridge
pressure is still at range. I used two pumps at the same time and the
fridge pressure dropped.
I tried to rotate the needle valves, but it was hard to move.
I also do not have any experience to do that.
As for my case, it may not relate to the sensor problem.
Best,
Tianzhi
> From: main_at_ammrl.groups.io on behalf of Matthias Brandl via groups.io
> Sent: Wednesday, October 15, 2025 1:26 PM
> To: main_at_ammrl.groups.io
> Subject: Re: [AMMRL] 800 Oxford pump magnet fridge vacuum problem
Dear Tianzhi,
I am not familiar with pumped Oxford magnets (only Bruker ones), so I am
probably asking some stupid questions, please bear with me:
- What other magnet monitoring data do you have? Specifically, do you
have coil temperatures or a flow sensor in the pumped helium stream? Did
any of these change when the pressure (apparently) changed?
- Do you have valves in the vacuum line that would allow you to isolate
sections of the line? What happens if you (briefly) close the line from
the magnet, does the pressure reading reach a reasonable value for the
pump or is it too high? Is the reading the same no matter where you
close off the line?
My thought is that you might have a drifting pressure sensor. A few
months ago, we had a case of "high pressure" (of course on the weekend)
on one of our Bruker systems, and in the end it was just a bad sensor.
Best,
Matthias
On 15/10/2025 20:09, Wang, Tianzhi via groups.io wrote:
>
> Dear all,
> I’m having a vacuum issue with my 20-year-old Oxford 800 MHz pump
> magnet. Recently, the fridge pressure suddenly increased from *15 to 21
> *and**stayed 21 for more than 1 year, although it’s still within the
> specified range (*9.2–25*). I also replaced the pump without any change
> of the pressure.
> I’ve tried to locate the source of the vacuum leak but haven’t had any
> luck so far.
> Has anyone experienced a similar issue or can offer suggestions on how
> to diagnose or address this type of vacuum leak?
> Alternatively, could anyone recommend a qualified engineer or service
> provider familiar with Oxford pumped magnet systems who could take a
> look at it?
> Thank you very much for your time and help.
>
> Best,
> Tianzhi
>
> -------------------------------------------------------------------
> Tianzhi Wang, Ph. D.
> NMR Manager
> Sealy center for Structural Biology & Molecular Biophysics
> University of Texas Medical Branch,
> 301 University Bvld, NMR dockside building, Rom 1.104
> Galveston, TX 77555-1157
> Email: tiawang_at_utmb.edu <mailto:tiawang_at_utmb.edu>
> (409)7476821 (O)
>
>
--
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 Wed Oct 15 2025 - 15:13:28 MST