Hi Piotr,
Increased time to cool down sounds similar to a transfer line I dealt with
that would slowly lose its vacuum over weeks/months. We got used to periodially
pumping it down thanks to a colleague letting us borrow a convenient vacuum
setup. I noticed the line would act "suspiciously" even before it went bad
enough to form condensation. Feeling the stinger above the dewar (carefully!)
for how cold it was can give an impression, though it took practice to self
calibrate.
Not sure about the elevated dewar pressure. Is it abnormally high right from
the beginning or does it spike after going into the magnet?
Kind regards,
Luke
Luke Fulton, PhD
CHEM BLDG R003
NMR Core Facility Director
Unit 3060
COR2E & Department of Chemistry
55 N Eagleville Road
University of Connecticut
Storrs, CT 06279
email: fko24003_at_uconn.edu
(alias): luke.fulton_at_uconn.edu
mobile: (603) 953-5275
Office: (860) 486-4069
________________________________
> From: main_at_ammrl.groups.io on behalf of Piotr Dobrowolski via groups.io
> Sent: Friday, July 12, 2024 12:10 PM
> To: main_at_ammrl.groups.io <main_at_ammrl.groups.io>
> Subject: [AMMRL] Helium fill problem
Dear NMR Managers,
Recently, we started having problem with helium fill on our old (about 25
years) 500 MHz Inova. Transfer line precooling takes a little longer than
before (I think) but there is no water condensation on the line. However,
from the beginning of the transfer the pressure in the transport dewar (60 L)
is high. We try to keep it below 2 psi by setting low gas flow (about 2 L/min).
I guess because of that the fill takes very long time - about 1 hour to
transfer 50-55 L. Unfortunately, our Oxford helium level monitor does not
work. We just fill-up every 3 months.
I've been taking care of this magnet for more than 6 years and the fill was=
always efficient (20-25 minutes) with gas flow set to 5 L/min (pressure 1.5-2 psi).
Transfer line vacuum was pumped last year.
Has anyone experienced such issue? Does this indicate transfer line or magnet
problem?
Thank you,
Piotr
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Received on Fri Jul 12 2024 - 09:55:59 MST