Dear Yong-Wah,
that's odd - normally the Oxford deflector (thin, 10 mm side of the line) should
indeed fit a Bruker transfer line - the thread is normally the same. What does
not fit is the thick, 12 mm side as well as any Magnex/Varian/Agilent deflector
(12/12.5 mm).
Indeed it is mandatory to swap the deflector against the straight end piece
(not only threaded end) for the purpose of pre-cooling a magnet with helium
(now insert the transfer line all the way until a snug fit to the funnel
is achieved) because now you *do* want to push all helium to the bottom of
the magnet.
I know some customers who are meticulous about collecting every single liter
of helium gas who are pre-cooling the transfer line while already inserted
into the magnet so as to catch even the evaporating helium used to precool
the line. In this case it is *veeery* important to use the deflector...
Cheers
Bert
> Am 23.06.2025 um 19:57 schrieb Kim, Yong Wah via groups.io:
>
> 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
>> 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 mor=
e 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
>>
>>
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