Dear All,
A quick update on this issue from a few months ago. First of all, big
thanks to Walt Niemczura for the following recommendation as it turned out
to be a very simple temporary workaround to the flow problem we were
encountering during the He fill. Walt had encountered a similar issue on
his Oxford magnet in the past and recommended pulling the transfer line up
1-2 inches after inserting it all the way into the fill port. Lo and
behold, we did the same thing and reached historically similar flow rates
from the exhaust port of the magnet during the fill with similar dewar
pressures. It is either icing or some sort of architectural blockage where
the disperser on the tip of the transfer line can't push the liquid as
efficiently depending on its position. Either way, we will likely keep
doing the fills this way and leave the problem alone assuming it won't get
worse and cause further flow/pressurization issues with the magnet.
Ideally, we would warm it up and purge the can when we get the
funds/down-time.
Many thanks again Walt!
Best,
Hasan
On Fri, Aug 22, 2025 at 5:52 AM Hasan Celik <hcelik_at_berkeley.edu> wrote:
> Hello All,
>
> We have an AS500 magnet that is from 2003 but was rebuilt during a move in
> 2019. We recently noticed during a helium fill that the flow rate coming
> out of the exhaust is significantly lower than usual and we have to put
> more pressure to get the liquid transfer going, indicating a
> likely blockage. This was rather surprising because the exhaust port is
> behind a check valve all the time and we regularly check the o-rings on the
> commonly disconnected ports, like fill, exhaust, etc.. After some detective
> work, we figured out that the small o-ring on the cap, where the helium
> level sensor is plugged into the tower, crumbled and was barely holding on.
> I tried checking for ice down the fill port with a thumper but we had just
> filled the magnet and the tip of the thumper quickly reached the surface of
> the liquid bath without hitting any ice. I didn't feel comfortable fishing
> around blindly down there. I believe that the sensor goes down the tower
> into the can parallel to the fill port so it is not clear to me where and
> how the potential ice blockage is impeding the liquid flow. Unfortunately
> the magnet book doesn't show the inner architecture of the magnet.
>
> We think that the exhaust for the magnet is fine as the flow rate for boil
> off has not changed from historical values. We should be fine in the short
> term but this is a problem I would like to resolve before it becomes a
> larger issue. I am wondering if anyone successfully dealt with a similar
> issue on one of these AS500s?
>
> I think my only remaining option, short of warming up the magnet, is to
> blow warm helium gas into the fill port when the helium level is lower. The
> top of the coil is at 5% sensor level according to the magnet book, and we
> generally fill the magnet when it hits ~45-50% (it is a nice full 60 L fill
> with a single dewar). I think the ice level is likely down there at the
> physical location of the corresponding sensor level. So a gentle consistent
> flow of RT helium gas at around 50% level may potentially solve the issue.
> Does anyone have tips for this as this will be our first attempt for a
> procedure as intrusive with a magnet?
>
> As usual, many thanks in advance to the community.
>
> Best,
> Hasan
>
>
>
> --
> _____________________________
> Director, PMRC Core NMR Facility
> College of Chemistry
> University of California, Berkeley
> 227A Hildebrand Hall
> Office: (510) 643-9829
> Cell: (949) 732-8175
>
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_____________________________
Director, PMRC Core NMR Facility
College of Chemistry
University of California, Berkeley
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Cell: (949) 732-8175
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Received on Wed Nov 05 2025 - 07:55:12 MST