Hi all,
I handle it the same way as Karel - only re-evacuate if it is actually
needed. Talking to some engineers, I was told that it is useful to pump
transfer lines for quite a long time, and maybe also assist the process
with a heatgun, as they are such long and narrow vessels.
The cold spot shown in Bob's picture is present to some degree in (I
think) all the transfer lines I have ever used. I have rarely seen frost
there, but almost always liquid condensation.
One further thing to note about pumping transfer lines: I have had a
case where I could evacuate the line perfectly well, but every time I
went to use it afterwards, it would suddenly lose its vacuum after
working fine for a couple of minutes. Maybe some crack that only opens
up when the line is cold? Anyway, the lesson is to not rely on the warm
line holding vacuum, as it might fail when cooled down.
Cheers,
Matthias
On 10/07/2024 23:51, Karel Klika wrote:
> Dear all,
>
> I have never done a pre-emptive evacuation of a helium transfer line, normally just wait till it is needed (once only in a previous location). The transfer line I am using at the moment actually could do with a pump down, it frosts up initially but once the adsorbent inside the transfer line gets cold enough the vacuum is good enough and the outside of the transfer line defrosts. The reason for my tardiness is that soon we will be getting a new system, and a new transfer line will be coming with it.
>
> Regards,
> K. Klika
>
> ________________________________________
> From: main_at_ammrl.groups.io <main_at_ammrl.groups.io> on behalf of Bob Berno <bberno_at_mcmaster.ca>
> Sent: 10 July 2024 23:49
> To: main_at_ammrl.groups.io
> Subject: [AMMRL] AMMRL: Helium transfer line gone soft.
>
> Hello everyone,
>
> Last August there was a useful email exchange here on the AMMRL about
> repairing helium transfer lines. I have a related question.
> Do any of you perform a preemptive pump-down of your transfer line(s),
> or do you wait until you see signs that the transfer line has lost vacuum?
>
> You can probably guess the reason I ask.
> Last week we aborted a helium fill when I saw excessive
> frost/condensation begin to form on the transfer line just as we started
> cooling it down.
> We aborted the transfer and then completed the helium fill using another
> transfer line.
>
> I asked the person in charge of our helium recovery system to test the
> suspicious transfer line. When he connected it to his pumping station,
> he could tell that it had indeed lost vacuum. He left it pumping
> overnight. Then on Friday morning he closed the valve, disconnected the
> pump and let the transfer line sit over the weekend. When he come in
> Monday morning, he found that it had maintained a good vacuum over the
> weekend, so he doesn't think there is a leak, but that it simply had
> lost vacuum.
> To test that, this morning we did a scheduled helium fill of another
> magnet to see how the freshly pumped transfer line performs.
> The fill went smoothly enough, but we did see a small cold spot on one
> of the welds (photo found at this link:
> https://photos.app.goo.gl/377BQgQZWrqyV4tj8 ) which we didn't see before.
>
> Strangely, this is the newest of my transfer lines - about 4-years
> old. The second transfer line I used last week is more than 14 years
> old and it has never been pumped down since we received it. And I have
> two other transfer lines that are each more than 20-years old and seem
> to be fine.
>
> And so I was wondering if anyone performs a preemptive pump-down of your
> helium transfer lines. If you do, how frequently do you do so? Every
> year? Every five years? Or do you wait for the first signs that the
> transfer line might be going soft?
>
> Cheers,
> Bob.
>
> --
> Dr. Bob Berno
> Manager, NMR Facility
> McMaster University, ABB-156
> 1280 Main St. West
> Hamilton, ON L8S 4M1
> T: 905-525-9140 x24158 or x24686
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--
Dr. rer. nat. Matthias Brandl (he/him or they/them)
Technical University of Munich
TUM School of Natural Sciences - BNMRZ
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Received on Wed Jul 10 2024 - 16:21:41 MST