Hi All,
Yes, it has been an informative thread.
In our older magnets, we use a deflector tip on the transfer line. Bruker
transfer line does not have a deflector tip. Which may speed up liquid
Helium transfer. While inserting the transfer leg into the magnet, it could
drag the warmer helium gas into the magnet. The deflector tip will probably
pull helium into the magnet from the other ‘legs’! Possibly contributing
to a larger initial outflow of Helium gas. I would like to know whether
we should use a deflector tip.
We have a separate line for the regular boiloff gas from all the magnets
feeding through a single mechanical back pressure controller. During liquid
helium transfer, the magnet exhaust opens directly to the 2” return line,
without any in line check valve. The pressure in the other magnets is not
affected. The valve should be open for a few minutes before inserting the
transfer line to bleed off the pressure in the magnet. This should reduce
the amount of helium vented and reduce the freezing of the port and o-ring
when inserting the transfer line.
There should not be any moving parts and a minimum of joints near the exhaust
of the magnet. The ball valve is situated after the heat exchanger. It does
not have any ice frosting during helium transfer. However, slight frosting
is observed at the T-joint where the heat exchanger meets the 2” return
line because the gas flow is mostly laminal and the central core of gas
flow is colder than the outer rim.
We do not have a bag. The helium gas is stored in 3 X 1000-Liter tanks.
I bench tested the mechanical back pressure controller. It maintained the
set pressure even when the exhaust side is a few tens of Torr. However,
higher pressure than the set pressure on the exhaust side is showing up on
the intake side. A 0.5 psi pop off valve is inserted in the body of the
back pressure controller to prevent the pressure buildup in the system.
Samrat, I like your pressure displays. Could you please tell me where I
can get this equipment. Thanks
Best Regards
Yong-Wah Kim, PhD.
Director of NMR Facility
The University of Toledo
________________________________
> From: main_at_ammrl.groups.io on behalf of Samrat Amin via groups.io
> Sent: Thursday, June 19, 2025 3:29 PM
> To: main_at_ammrl.groups.io
> Subject: [EXTERNAL] Re: [AMMRL] Quench narrowly avoided? Filling small magnets connected to helium recovery
Hi All,
This has been a very informative thread, and I'm learning quite a bit here!
We've run into several similar issues on our system and we have some data on
it, so I wanted to share our experiences in case it helps anyone.
We have a Cryomech recovery system installed with two large bags, and a 2"
recovery line that connects all the manifolds (made up of 3/4" to 1" lines)
at each magnet. We have two HRCP compressors that pump on the bags and store
the helium in 20 medium pressure tanks.
Fills and Line Pressure: We have Bruker one-way valves installed on all of
our magnets (including our Varian magnets), and we have been filling through
these check valves (ie, we don't bypass or remove them) for the last couple
years without any problems. We always isolate all the magnets during a fill
(magnets not being filled are vented to atmosphere while we collect helium
only from the magnet we are filling). This creates quite a bit of pressure
(~0.4 PSI) in our manifold and the main helium line that connects to our bags.
I've attached a figure which shows the pressures generated at the manifold and
in our main line near the bag during a fill. The high line pressure would
effectively stop the boiloff from other magnets if they are not isolated during
a fill.
Vacuum on Magnets: I'm glad this question was asked as our laser sensors
have been very problematic since we installed the system a few years ago.
Since then, we've had compressors turn on several times automatically and
the bottom laser does not trigger a turn-off. This resulted in scary
situations where our bags and helium line were vacuumed. Despite having
back-pressure regulators installed, we noticed that the magnets were being
pumped. The compressors eventually turned off on their own after a certain
vacuum level was detected, but this was well after our magnets felt the problem.
I've attached 3 figures showing the boiloff from our magnets reaching 10x
normal levels while they were being pumped. Even our actively pumped
magnets felt it and went into panic mode (the Bruker 850 switched both pumps
on for a while until we caught it). Luckily we didn't experience any quenches,
but I do worry what could have happened if this was not caught. Speaking
with Cryomech on the issue, they confirmed that a vacuum sensor is installed
on the HRCP compresors, but the setpoint may not be adequate to protect a
magnet (Presumably it can be fixed by a firmware update?). We definitely
don't want to rely on the compressors. The info on this thread makes me
wonder if our back-pressure regulators are installed/set correctly. For
those that have installed these, it would be great if you can share details
about the setup and setpoints.
Thanks,
Samrat Amin
Magnetic Resonance Research Center
Arizona State University
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Received on Fri Jun 20 2025 - 12:55:35 MST