My Quantum Design Helium Recovery System is a Direct Recovery system. We
chose this system due to a combination of space and cost savings. The system
has advantages and disadvantages and tradeoffs.
Advantages:
*
Cost Savings (~$100K)
*
Space Savings
*
No bag or additional tanks for a low or medium pressure recovery system.
*
Cleaner helium as the helium flows directly through a dryer and into the liquefier.
Disadvantages
*
No recovery during fills
*
Compressor runs 24/7
*
Back Pressure on the magnets is higher - currently 0.7psi
This last point regarding magnet back pressure is where my concern lies.
Previously, we had a back pressure on our magnets of about 0.5psi coming
from the helium recovery system. This back pressure was due in some part
to the dryer and also check valves in the liquefier. During fills we would
need to slowly vent that pressure before a fill.
After our lab flood, we received a new QD system. This is a newer model and
we are experiencing a backpressure increase to about 0.7psi on our magnets.
We are expressing our concern with this higher level of back pressure with
Quantum Design and trying to pin down what the backpressure should be with
this direct recovery system.
I want to get a better understanding of the risks of this pressure. Here
are my thoughts - please correct me where I'm wrong:
1.
Higher backpressure means colder LHe temps in the magnet
2.
During fills, the pressure must be vented. This will lead to a higher LHe temp.
I don't know how much of a temperature change there will be, but I expect
that temperature stability is important.
3.
Venting 0.7 psi is losing additional helium (I don't know if it's significant).
4.
And most importantly - What is a safe long-term pressure for a NMR magnet?
The relief valves on the top of the magnets are 1psi? 2psi?
*
We have a old (35 yo) Oxford, several Magnex magnets, and a several Bruker magnets.
Ken Sharp-Knott
Manager of Analytical Services and the NMR Facility
Department of Chemistry
Virginia Tech
(540)267-6502 (Cell)
(540)231-0885 (Office)
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Received on Mon Aug 04 2025 - 05:03:00 MST