Hello everyone,
First, I will apologize for inadvertently sending the original message twice.
Second, I want to thank everyone who responded so quickly. Several
responded to the whole group so you have all seen those already. I also
received several direct responses.
I thought I would put together a brief summary before I forget. Here are
some key points that came up:
* There are a few of you who routinely pump down your transfer lines
on roughly an annual basis.
o This has the potential added benefit of improving helium
transfer efficiency.
o This also assumes that you have easy access to a turbo pump and
the proper fittings/accessories.
* Many others wait until they have a reason to check the vacuum.
* One person mentioned having a HTL which would pump down and hold
vacuum fine, but would leak when cooled to liquid helium temperatures.
o Therefore, the ultimate test is to transfer liquid helium.
Micro-fractures are more evident at low temperatures.
* They don't make them like they used to....
o Several people commented that the older HTLs seemed to be more
substantial and would last much longer than the newer ones.
This has been my experience as well.
* Inspect your valves and o-rings:
o Bert offered a good suggestion that if you are going to the
trouble of pumping down your HTL, take a few minutes to inspect
the valve and o-rings (our first line of defence). NOTE: when
you break vacuum to disassemble the valve, use dry nitrogen gas
to reduce moisture exposure.
* Solder/weld joints are vulnerable:
o It is fairly common to see condensation in the cold-spot area I
showed in the photo (especially when the humidity is high).
o Make a note of this and monitor if it seems to be getting worse
during subsequent fills.
o If you start seeing the condensation freeze, like I showed in
the photo, then that can be a greater concern.
For those of you with pumped magnets that use the special two piece
transfer lines: these HTLs typically come equipped with proprietary
vacuum ports which require special and expensive accessories if you want
to pump them down. Last year, Daniel Holmes reported that when he had
his 900 MHz HTL repaired by Cryofab, he asked them to replace the
proprietary vacuum port with out like he has on the rest of his HTLs. =
What a great idea!
So, what am I going to do?
I think we will continue as we have been doing- we will pump down the
transfer lines if we see there is a problem. If we do not see any signs
of a problem with a transfer line, we will just keep using it.
For the transfer line which gave us a problem last week: we will test
the vacuum again before we next use it. If the vacuum remains good, we
will use it. And we will continue to monitor the fills rather closely
to see if the cold spot is getting worse.
Cheers,
Bob.
On 2024-07-10 4:49 p.m., Bob Berno via groups.io wrote:
>
> 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
> -------------------------------------------------------------------------
>
> This email contains CONFIDENTIAL information intended for the specific recipient(s).
> If you have an accommodation need for a planned meeting, please e-mail me directly and
> I will do my best to make appropriate arrangements.
> Should you require any materials sent via this e-mail address in an alternate/accessible
> format, please let me know.
>
> McMaster University sits on the traditional Territories of the Mississauga and
> Haudenosaunee Nations, and within the lands protected by the "Dish With One Spoon"
> wampum agreement.
>
--
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
---------------------------------------------------------------------------
This email contains CONFIDENTIAL information intended for the specific recipient(s).
If you have an accommodation need for a planned meeting, please e-mail me directly and
I will do my best to make appropriate arrangements.
Should you require any materials sent via this e-mail address in an alternate/accessible
format, please let me know.
McMaster University sits on the traditional Territories of the Mississauga and
Haudenosaunee Nations, and within the lands protected by the "Dish With One
Spoon" wampum agreement.
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Received on Tue Jul 16 2024 - 12:33:53 MST