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 on behalf of Bob Berno
> 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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Received on Wed Jul 10 2024 - 14:52:05 MST