Hi Ken,
I’d agree with the engineer, and might even go a step further. We pump
our lines down roughly once a year, but we’ve also been able to make
some good apples-to-apples comparisons on transfer efficiency when we’ve
replaced some older lines with new ones.
In both cases we replaced a line that would pump down well, but needed to be
pumped more often than we’d like.
In both cases replacing the lines reduced the total mass of helium required
to fill their respective magnets by approximately 20%. The difference is
entirely in gas produced during the fill process.
We recover our line cooling gas and fill exhaust gas, so it wasn’t
making a difference in our overall recovery statistics; but it did surprise
us how large of a difference the line makes.
If you’re not collecting line cooling gas and fill exhausts, transfer
line maintenance is helium saved!
Best,
Alex
Alex Paterson
The National Magnetic Resonance Facility at Madison (NMRFAM)
University of Wisconsin-Madison
alpaterson_at_wisc.edu
> From: main_at_ammrl.groups.io On Behalf Of Kenneth Sharp-Knott via groups.io
> Sent: Wednesday, July 30, 2025 11:27 AM
> To: main_at_ammrl.groups.io
> Subject: Re: [AMMRL] Helium Transfer Lines - Refreshing vacuum. #poll-notice
Just to follow-up... The reason I ask is the engineer mentioned that most
people wait far too long. By the time you see evidence of it having gone
soft, you have likely been losing quite a bit of helium due to excessive
boiloff for some time.
Apparently most transfer lines also come with the necessary equipment to pump
it down. They were some of the bit and pieces lying around the lab that I
had no idea of the purpose.
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