NMR Folks,
Thanks, for the nearly 40 responses received in the first day.
About 42 % routinely re-evacuate the helium transfer line every 6
months to 2 years. A few do it before each fill.
About 34 % re-evacuate only after cold spots or frost are
noticed. Still, 2 to 12 years passed before the cold spots developed.
About 24 % have never re-evacuated the line over periods of 3 to
17 years.
Of those who re-evacuate, about 1/2 use a standard rotary pump,
letting the liquid helium cryopump the remaining air. The other 1/2 use a
turbo or diffusion pump. Practically everyone does it locally even if they
send it to another department on their campus. Most use a liquid nitrogen
trap between the pump and line.
One said that the line becomes more flexible when it has lost the
vacuum.
Our solution: We will just watch for the cold spots. Several of you
pointed out the fitting with the built-in hex-adjuster which has always
been sitting in the Oxford magnet kit. We will use that, if necessary, to
avoid a Swagelock valve. Thanks, again!
Ed Waali
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Edward E. Waali
Department of Chemistry
University of Montana
Missoula, MT 59812
Voice: (406) 243-4992
FAX: (406) 243-4227
E-mail: waali_at_selway.umt.edu
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Received on Fri Dec 20 2002 - 16:24:21 MST