Date: Thu, 19 Jun 2025 12:29:15 -0700
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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(image/png attachment: Vac_Overview-2.png)
(image/png attachment: Vac_Zoomed-2.png)
(image/png attachment: Vacuum_1.png)
(image/png attachment: LinePressure_850Fill.png)