Hi
If the transfer line is losing vacuum slowly could it be the o ring on the
valve is bad or damage to the valve seat? Otherwise it would have to be some
micro crack or a bad weld which seems less likely…
regards
Gary
Dr Gary S Thompson NMR Facility Manager
CCPN CoI & Working Group Member
Wellcome Trust Biomolecular NMR Facility
School of Biosciences, Division of Natural Sciences
University of Kent, Canterbury, Kent, England, CT2 7NZ
01227 82 7117
g.s.thompson_at_kent.ac.uk
orchid: orcid.org/0000-0001-9399-7636
On 12 Jul 2024, at 17:57, Michael Groves via groups.io wrote:
Hi Piotr,
My first suspicion would be icing somewhere in the magnet. If the exhaust
is partially blocked then you'd get higher back pressure with a lower flow
rate, which sounds like what you're seeing. Or if the transfer line is
running into ice somewhere and getting partially blocked then you'd get less
flow as well. Is the o-ring on the fill port in good shape?
It sounds like your transfer line might be okay based on the lack of ice/wet
spots. You might also check the normal exhaust flow from the magnet--if the
boil-off has increased and more helium is boiling off between fills then the
fills would take longer. And this would show up in increased helium exhaust
from the magnet under normal operating conditions. However I wouldn't expect
that to cause higher back pressure--just longer fills.
Cheers,
Mike
On Friday, July 12, 2024 at 10:21:08 AM MDT, Piotr Dobrowolski wrote:
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 - 10:44:33 MST