Thanks Bert,
For an excellent / definitive answer. I knew about the funnel because I
needed to restart our 400 MHz magnet and was reminded about it in the manual.
It is so easy to go "automatic" and forget about important details!
Does anyone know where to get a "flame deflector" tip that will fit a Bruker
transfer line. The ones on my Oxford transfer lines do not fit the Bruker line.
With respect to precooling the transfer line, the deflector may give me more
control over the rate at which I can insert the transfer line into the magnet
and minimize the size of the initial burst of helium gas during liquid helium
fills. We would like to hear how some of you approach this issue.
Thanks
Yong-Wah Kim, PhD.
Director of NMR Facility
The University of Toledo
________________________________
> From: main_at_ammrl.groups.io on behalf of Spin-Doc via groups.io
> Sent: Monday, June 23, 2025 11:44 AM
> To: main_at_ammrl.groups.io <main_at_ammrl.groups.io>
> Subject: [EXTERNAL] Re: [AMMRL] Quench narrowly avoided? Filling small magnets connected to helium recovery
Hi,
all Oxford magnets but also Magnex/Varian/Agilent magnets indeed use a "flame
deflector" and it is discouraged to refill helium without it (even more so
with Oxford magnets):
The magnet have a funnel at the bottom of the helium refill turret (in
Magnex/Varian/Agilent this funnel is only on the "left" turret containing the
wiring where refilling should be done only in emergency case because of all
the cables going down there). This funnel has a long tube attached going all
the way to the bottom plate of the helium dewar (for better cooldown efficiency).
With a straight transfer line exit this funnel may push any helium gas (in
case the refill dewar is empty or a vacuum issue in the transfer line) down
towards the bottom of the magnet, which then bubbles up along the magnet,
possibly "warming" up exposed supercon wires like those going to the switches.
This can lead to a quench… The minimum is to never insert the transfer line
all the way but this is a bit hard to do exact and it may also slide
down over time during the refill.
There may be a bit higher helium boiloff at the beginning simply because the
liquid helium sprays upwards, where it can touch "warmer" parts of the magnet.
For safety reasons I'd rather keep using the deflector
Cheers
Bert
Am 20.06.2025 um 21:53 schrieb Kim, Yong Wah via groups.io:
Hi All,
Yes, it has been an informative thread.
In our older magnets, we use a deflector tip on the transfer line. Bruker
transfer line does not have a deflector tip. Which may speed up liquid Helium
transfer. While inserting the transfer leg into the magnet, it could drag
the warmer helium gas into the magnet. The deflector tip will probably pull
helium into the magnet from the other ‘legs’! Possibly contributing
to a larger initial outflow of Helium gas. I would like to know whether
we should use a deflector tip.
We have a separate line for the regular boiloff gas from all the magnets
feeding through a single mechanical back pressure controller. During liquid
helium transfer, the magnet exhaust opens directly to the 2” return line,
without any in line check valve. The pressure in the other magnets is not
affected. The valve should be open for a few minutes before inserting the
transfer line to bleed off the pressure in the magnet. This should reduce
the amount of helium vented and reduce the freezing of the port and o-ring
when inserting the transfer line.
There should not be any moving parts and a minimum of joints near the exhaust
of the magnet. The ball valve is situated after the heat exchanger. It does
not have any ice frosting during helium transfer. However, slight frosting
is observed at the T-joint where the heat exchanger meets the 2” return
line because the gas flow is mostly laminal and the central core of gas
flow is colder than the outer rim.
We do not have a bag. The helium gas is stored in 3 X 1000-Liter tanks.
I bench tested the mechanical back pressure controller. It maintained the set
pressure even when the exhaust side is a few tens of Torr. However, higher
pressure than the set pressure on the exhaust side is showing up on the
intake side. A 0.5 psi pop off valve is inserted in the body of the back
pressure controller to prevent the pressure buildup in the system.
Samrat, I like your pressure displays. Could you please tell me where I can
get this equipment. Thanks
Best Regards
Yong-Wah Kim, PhD.
Director of NMR Facility
The University of Toledo
Magnetic resonance equipment, service, training & more
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Received on Mon Jun 23 2025 - 12:33:38 MST