David,
Older instruments do not use check valves and use latex or similar tubing for exhausting nitrogen gas.
I have one 20 year old instrument with that setup, but I've never had ice buildup inside.
I fill nitrogen before the helium fill and keep the tubing in good condition.
Newer Bruker instruments have polyurethane tubing connected together with push in fittings to form a system with a check valve.
The Bruker engineer showed me that at each fill the tubing needs to be tested that they are securely in the fitting as they do come loose – and when they are loose, you have an open system, and air can get in.
Cheers
George
From: David Richardson <David.Richardson_at_ucf.edu<mailto:David.Richardson_at_ucf.edu>>
Date: Wed, 24 Aug 2016 13:42:35 +0000
To: AMMRL <ammrl_at_ammrl.org<mailto:ammrl_at_ammrl.org>>
Subject: AMMRL: RE: very scary nitrogen fill
Hi all,
Is it not standard to put a check valve (or one-way valve/back-flow preventer valve, whatever the appropriate name may be) on the nitrogen exhaust? I have never worried about the negative pressure in the nitrogen can during a helium fill because of the check valve, but with as long as this conversation has gone on without mention of using a valve I am starting to wonder if I need to consider the pressure despite using the valve.
David
David Richardson, Ph.D.
NMR Instrumentation Specialist
Chemistry Department
University of Central Florida
david.richardson_at_ucf.edu<mailto:david.richardson_at_ucf.edu>
407-823-2961
http://chemistry.cos.ucf.edu/nmr/
Received on Wed Aug 24 2016 - 09:23:14 MST