Hi Bert,
For fills on certain magnets I use the storage dewar's pressure builder
and built-in pressure gauge (which I know isn't terribly accurate). In
that case, I try to keep the pressure on that gauge around 3-5 PSI. (I
you just keep the pressure builder on, it cycles between ~3 and 6 PSI -
I usually turn it on and off to prevent the pressure from getting too
high)
For other magnets I use a helium cylinder to pressurize the dewar. With
that setup I have a pressure gauge and flow meter between the incoming
gas and the vent. In that case I keep the pressure shown on that gauge
between 2 and 3 PSI.
In both cases I watch the pressure gauge on the recovery line closely.
During the bulk of the fill, that one will show between zero and 0.5 PSI
(mostly depending on how full the collection bag is). When the bag is
near empty, that pressure gauge will read near zero even when I'm using
the pressure builder and the dewar gauge reads 5 PSI. When the magnet is
full, that pressure gauge shoots up quickly. I turn the flow off before
it hits 1 PSI.
I feel like I do my fills relatively quickly. On a couple of ancient
Oxford 500s, the fill volume is ~30L and I try to keep the pressure as
low as possible (say 2 PSI on the gauge going into the vent). Those
fills take about 15 minutes. On my 800 US2 magnet, I use the pressure
builder and higher pressure and I fill 100L in ~30 minutes.
Thank you to everybody - this has been a really useful thread!
-Robert
On 2025-07-31 14:55, Spin-Doc wrote:
> Hi Robert,
>
> What is the pressure in the storage dewar you use during transfer?
> And how much back pressure do you have in the recovery line next to
> the magnet during refill?
> Both of these will determine the speed at which you fill the magnet -
> the slower it is the longer the contact time of liquid helium inside
> the transfer line. And losses will be higher with longer contact time
> (only to be even worse if the vacuum is bad). All I’m saying is your
> vacuum may be perfect but you may still have losses if filling slowly…
>
> Cheers
> Bert
>
>
> -> Sent via mobile <-
>
> Spin-Doc
> Magnetic resonance equipment, service, training & more
> Dr. rer. nat. Bert Heise
> Owner, applications scientist
> Kiefernweg 13
> 58239 Schwerte
> Germany
> Web: http://www.spin-doc.net
> Mail: bert.heise_at_spin-doc.net
> Phone: +49-171-5135315
>
> Representing MestreLab, Stelar & Barthel HF
>
>
>
>> Am 31.07.2025 um 19:26 schrieb Robert Peterson via groups.io
>> <peterson=mbi.ucla.edu_at_groups.io>:
>>
>> Bert,
>>
>> For my fills these days I use a "new" (2021) transfer line. It's from
>> Cryofab and it breaks apart into two pieces - I have two "fill lances"
>> of different sizes. I've never pumped it. I guess I assumed that it
>> was good when I got it. It doesn't have any cold spots though. Once
>> the fill gets going, the whole thing (including the top of the section
>> that goes into the dewar) is warm and dry. Would it still be a good
>> idea to pump it? I do have access to a turbopump.
>>
>> Since installing the helium recycling system and being able to
>> quantify the boiloff gas, I've always recovered ~30% as gas. I have
>> used several different transfer lines, and the boiloff amount has
>> always been roughly the same (although none of the other ones had been
>> recently pumped down either).
>>
>> OK, I guess I've answered my own question: I'll try pumping the line
>> and see if I get less boiloff gas.
>>
>> -Robert
>>
>>> On 2025-07-30 00:28, Spin-Doc wrote:
>>> _at_ Robert:
>>> A loss of a whopping 30% at each refilll does sound a bit excessive
>>> to
>>> me and triggers some questions:
>>> - do you use one single helium transfer line each time? Sure that its
>>> vacuum is still OK? Tried to open its valve, clean & re-grease the
>>> O-ring and pump out on a turbo for a few hours?
>>> - what is the pressure in the helium dewar used during transfer?
>>> -> Sent via mobile <-
>>> Spin-Doc
>>> Magnetic resonance equipment, service, training & more
>>> Dr. rer. nat. Bert Heise
>>> Owner, applications scientist
>>> Kiefernweg 13
>>> 58239 Schwerte
>>> Germany
>>> Web: http://www.spin-doc.net
>>> Mail: bert.heise_at_spin-doc.net
>>> Phone: +49-171-5135315
>>> Representing MestreLab, Stelar & Barthel HF
>>>> Am 30.07.2025 um 02:49 schrieb Kim, Yong Wah via groups.io
>>>> <Yong-Wah.Kim=utoledo.edu_at_groups.io>:
>>>>
>>>> Hello,
>>>> We have just installed a Medium pressure Helium recovery system by
>>>> Quantum Design, QD. We had recently transferred 119 liters of
>>>> liquid into our 600 MHz magnet. Our Renner helium compressor seems
>>>> to be able to keep up with the boiloff during liquid helium
>>>> transfer. We are told by the installers to keep the oil temperature
>>>> of the compressor below 60C. I would love to hear about your
>>>> experience with a similar system.
>>>> We had chosen the QD system with 3 X '1000-Liters' storage tanks
>>>> because the contamination level is much lower than the "bag' system.
>>>> So far it seems to be a robust system. We opted for a mechanical
>>>> backpressure controller and the pressure in the magnet do goes
>>>> through cycles of pressure fluctuations of less than 0.3 inches of
>>>> H2O every 90 seconds. No impact on NMR data has been detected so
>>>> far. The tanks have 29" diameter and 92" high.
>>>> Best regards
>>>> Yong-Wah Kim,
>>>> -------------------------
>>>> From: main_at_ammrl.groups.io <main_at_ammrl.groups.io> on behalf of
>>>> Sebastian Kemper via groups.io
>>>> <sebastian.kemper=tu-berlin.de_at_groups.io>
>>>> Sent: Tuesday, July 29, 2025 8:30 AM
>>>> To: 'main_at_ammrl.groups.io' <main_at_ammrl.groups.io>
>>>> Subject: [EXTERNAL] [AMMRL] Helium recovery - bag size
>>>> Hello everyone,
>>>> I would like to modify my helium recovery system so that I can
>>>> collect helium during the filling procedure. Due to the relatively
>>>> limited space, I have a few questions about balloon size and
>>>> compressor performance and I would be very grateful for any
>>>> experience from colleagues so that I can purchase the right
>>>> equipment.
>>>> - How much helium will be produced with a fill of 80-90 liters? I
>>>> calculated for 80 liters with a fill loss of 15% that max. 16 m³
>>>> will be released during the fill (assuming the cold replaced gas
>>>> will warm up from 4 K to 298 K). What are the real numbers? Are
>>>> there any empirical values?
>>>> - I probably only have space for a balloon of 10-12 m³. Do you have
>>>> a setting where the compressor starts during filling and compensates
>>>> for a balloon that is ‘too small’? A colleague told me, that it
>>>> is possible, but I don't want to miscalculate and it would be very
>>>> helpful to hear about other cases. If you have such a setting, what
>>>> size balloon do you have? What is the compressor's flow rate? At
>>>> what percentage of the balloon volume does the compressor activate?
>>>> Best regards,
>>>> Sebastian
>>
>>
>
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