Hi David,
That's a difficult question to answer.
The header itself doesn't have any shutoff valves to protect the magnets in
case relative pressure were to go negative. One of several ball valves would
allow manual intervention in a pinch. I believe the liquefier/compressor have
more practical automatic protections buried in their designs. They are dauntingly
complicated. Unfortunately, I don't think I can share those schematics without
souring relations with QT.
The system has multiple closed loops, sensors, and valve controls. My compressor
has several times triggered automatically and run overnight without bringing
header pressure <0.2 psi, or siphoning liquid from magnets. So in practice, the
magnets are protected from vacuum...somehow. It's not clear to me how many or
which components would need to fail before losing that protection.
Kind regards,
Luke
Luke Fulton, PhD
CHEM BLDG R003
NMR Core Facility Director
Unit 3060
COR2E & Department of Chemistry
55 N Eagleville Road
University of Connecticut
Storrs, CT 06279
email: fko24003_at_uconn.edu
(alias): luke.fulton_at_uconn.edu
mobile: (603) 953-5275
Office: (860) 486-4069
________________________________
> From: main_at_ammrl.groups.io on behalf of David Richardson via groups.io
> Sent: Friday, June 13, 2025 11:40 AM
> To: main_at_ammrl.groups.io
> Subject: Re: [AMMRL] Quench narrowly avoided? Filling small magnets connected to helium recovery
Hi Luke,
Ok, great. I must have misunderstood what you were saying as it sounded to
me like the only thing isolating magnets from one another were the ball valves
on the manifolds, which obviously wouldn't be ideal.
Since we are already having a recovery discussion, do you have anything in
place to prevent the compressor(s) from pumping on the magnets? This would
be the result of something else failing, but having had balloon sensors fail
(along with another incident where a student made a very poor decision to
flip the compressor into "manual-on" mode and leave for the night) I have
had my compressor draw a pretty impressive vacuum on the building-wide lines.
Regards,
David
David Richardson, Ph.D.
Director, NMR Facility and Cryogenic Services
Office of Research
University of Central Florida
david.richardson_at_ucf.edu
407-823-2961
http://sciences.ucf.edu/chemistry/nmr/
________________________________
> From: main_at_ammrl.groups.io on behalf of Fulton, Luke via groups.io
> Sent: Friday, June 13, 2025 10:41 AM
> To: main_at_ammrl.groups.io
> Subject: Re: [AMMRL] Quench narrowly avoided? Filling small magnets connected to helium recovery
Hi David,
The former. 3x magnets all connect to a shared copper pipe from which gas feeds
into the larger recovery equipment. Picture attached. Each magnet has its own
check valve to prevent exhaust from one magnet directly backflowing into the
other two. Those check valves should close if/when header pressure spikes.
There's an additional ball valve where the whip connects to the copper pipe.
I only use it to isolate the header in case of maintenance on whip/manifold.
This one does seal off exhaust off flow, which as Bert pointed out is dangerous
if closed and forgotten.
The copper header ranges from 0.2-0.29 psi and a small compressor pulls that
gas into the purifier/liquefier. If header pressure reaches 0.3 psi, as always
does during fills, a larger compressor moves gas into 3x medium pressure tanks
(MPT) for temporary storage. If for some reason the header reaches 0.4 psi then
a relief valve will open to vent excess pressure to atmosphere.
Conjecture on my part: I think everyone equips their magnets with a check valve
for routine operation to prevent atmosphere backfilling and creating ice blocks.
In labs without helium recovery, perhaps for half of the magnets we remove that
valve during fills and vent directly to atmosphere. Filling always pressurizes
the magnet. The question is how much, and technique and setup play a role. The
check valve adds a little more, 0.22 psi (15 mbarr) in my case, and the header
more on top of that. Empirically I think the dimensions of the manifold/tubing
can magnify those numbers, though my grasp on the physics is too slippery to
explain properly.
Kind regards,
Luke
Luke Fulton, PhD
CHEM BLDG R003
NMR Core Facility Director
Unit 3060
COR2E & Department of Chemistry
55 N Eagleville Road
University of Connecticut
Storrs, CT 06279
email: fko24003_at_uconn.edu
(alias): luke.fulton_at_uconn.edu
mobile: (603) 953-5275
Office: (860) 486-4069
________________________________
> From: main_at_ammrl.groups.io on behalf of David Richardson via groups.io
> Sent: Thursday, June 12, 2025 8:31 PM
> To: main_at_ammrl.groups.io
> Subject: Re: [AMMRL] Quench narrowly avoided? Filling small magnets connected to helium recovery
Hi Luke,
You mentioned they are chained together in some manner. Does the exhaust from
filling one magnet pressurize the other all way up to the ball valve? Or is
there an additional manifold and/or backflow control on the wall preventing
the exhaust of one from reaching the other?
Regards,
David
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