Date: Thu, 02 Apr 2026 13:49:30 -0700
Hi Jerry,
We have pretty good data on this. Please see the attached plot showing
line pressures during a small magnet fill (Bruker 400). This pressure
sensor is mounted on our recovery manifold closely after the Bruker check
valve, so its a good reading on what our recovery manifold is feeling at
all times. Ill try to answer your questions below:
1) During small magnet fills (showing Bruker 400 in the attached plot), we
typically see about ~0.1 PSI at the recovery manifold that the magnet is
attached to. The spikes in the data are probably real (I believe that
is due to us reading the magnet's helium level meter). We fill the
magnets through the Bruker check valve. We always bypass/vent the
other magnets during fills which is why they are not impacted during transfer
to any magnet. For small magnets, we typically pressurize the dewar
between 1-2PSI. We don't have concrete data on the efficiency vs
pressure, but we have seen it become less efficient at lower pressures on
our high-field magnet fills. We typically estimate about ~15-20% loss
in flashed gas during transfers.
2) We did not notice any difference in fill duration or efficiency between
venting to atmosphere vs venting to the recovery system. I suppose this
is largely dictated by the type of recovery manifold you have in place, so
I will mention that most of our manifold is made of 1" copper lines which
leads to a 2" (or 2.5"?) main trunk that leads to our recovery bags (we
have two).
3) For small magnets, we typically use 1-2PSI (seems to depend on the dewar
and transfer line diameter). For our Bruker 850 (pumped magnet),
we typically pressurize the dewar to 1.7-2PSI. For our old Varian
800 (which is a dual helium can magnet), we pressurize the dewar to 4 PSI
(this one is an oddity and probably doesn't compare to most magnet fills
out there). I mention the 800 because it is where we noticed the largest
difference in fill efficiency. We had huge losses when
transferring at 2.5PSI compared to 4PSI.
Hope this helps! Feel free to reach out if you have any other questions!
Samrat Amin
Magnetic Resonance Research Center
Arizona State University
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