Hi Jerry
The pressure in our recovery line is governed by the check valve we have going
into the bags. Under normal non-fill conditions and doing direct recovery
the check valve is set to 0.33 Psi but the liquifier is at 0.04 and because
of the check valve inside the liquifier line pressure is about 0.25.
During fills we open a 0.15 psi check valve that is in parallel with our 0.33.
This keeps fill pressure in the line at that pressure. We do not see pressure
increase above that once we start the fill.
There is a 0.15 psi check valve on each magnet so total line pressure at the
magnet is 0.3 PSI.
This is typically below the pressure we even get liquid from our transfer line.
For our 600s we fill at pressures of 1.5-1.7 PSI. It may be more efficient at 2.
But it will depend on the design of your line. But generally fills are more
efficient at higher pressure.
I cannot tell you if it is less efficient that venting directly to atmosphere
as I have never measured it. But I don’t notice a significant
difference in the fill time. Certainly not different enough to worry about,
esp when you are capturing 5-10 L of liquid equivalent back into your recovery
system which more than makes up for any extra time it takes
David Jones
Associate Professor
Dept. Of Pharmacology
University of Colorado
School of Medicine
Tel (303)-724-3600
On Apr 2, 2026, at 1:28 PM, Jerry Hu via groups.io wrote:
Dear AMMRL,
I would like to get input from those who operate complete helium recovery
systems that capture both NMR magnet boil-off and exhaust from magnet
refills.
1. During magnet refills, what is the typical pressure in the recovery line?
Does this pressure affect the fill efficiency (i.e., the volume of liquid
helium transferred to the magnet relative to the total volume consumed)?
2. When refill exhaust is recovered, is the fill duration significantly
longer compared to conventional fills (where the exhaust is vented to atmosphere)
at the same source pressure? How does the fill efficiency compare between the two cases?
3. What source dewar pressure do you typically use for magnet fills when the
exhaust is captured?
Your inputs are appreciated.
Cheers,
Jerry
-----------------------------------------------
Jerry Hu, Ph.D.
Technical Director, Project Scientist
Materials Research Lab, UCSB
Santa Barbara, CA 93106
Jerry.hu_at_ucsb.edu<mailto:Jerry.hu_at_ucsb.edu>
(805)893-7914 (office)
(805)893-7940 (lab)
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Received on Fri Apr 03 2026 - 07:37:25 MST