I've used the slit tubing with a stopper also, but please, I DO HOPE you
meant latex and not Tygon. Tygon hardened by LN contact is incredibly
brittle, strained and shatters almost explosively into long shards as sharp
as glass. Serious lacerations quite possible.
-----Original Message-----
From: Martha Morton [mailto:mmorton4_at_unl.edu]
Sent: Wednesday, August 24, 2016 3:14 PM
To: David Richardson; AMMRL
Subject: Re: AMMRL: RE: very scary nitrogen fill
Dear All,
All of my current magnets have check valves on the nitrogen ports. As David
Richardson suggested, this solves the problem of pulling in and solidifying
other gases in the liquid N2 port during a helium fill. Twelve years ago,
when I was in Connecticut, I had an unshielded 400 with no check valves on
the N2 ports. It was common for me to get blockages in the nitrogen ports
after helium fills. I talked to an engineer about it (Tony Dodaro, Triangle
Analytical). He suggested blocking the N2 ports with a piece of tygon tubing
with a few slits in it a few minutes before you start your helium fill. This
allows the nitrogen dewar to vent, but adds an effective block from other
gases. I would usually wait until about 30 minutes after a helium fill to
take this tygon tubing off. This remedy worked well and is cheap!
Please remember, if you have to do this, to put small slits in your piece of
tygon that you use to block those ports.
Best regards,
Martha
Martha Morton, PhD
Director of Research Instrumentation
University of Nebraska - Lincoln
Department of Chemistry
834 Hamilton Hall
Lincoln, NE 68588-0304
402-472-6255
________________________________
From: David Richardson <David.Richardson_at_ucf.edu>
Sent: Wednesday, August 24, 2016 8:42 AM
To: AMMRL
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/
From: William Thurmes [mailto:wthurmes_at_miyotadca.com]
Sent: Tuesday, August 23, 2016 13:00
To: Robert Peterson <peterson_at_mbi.ucla.edu>; AMMRL <ammrl_at_ammrl.org>
Subject: RE: Fwd: AMMRL: very scary nitrogen fill
Jerry Hatvany years ago taught me a trick on how to keep air from backing
into the nitrogen port: first, do an LN2 fill before the LHe fill, and then
roll a Kimwipe or tissue into a cigarette-type shape and stuff the end into
the N2 outgas tube. The Kimwipe keeps air out of the tube, but - here's the
key thing - if you forget to pull it out it pops out the next time the LN2
is filled. The only bad thing's a bit of litter every 4 months. (If you
forget to open a nitrogen vent port bad things might happen.) By the way,
when the LHe level is being checked during fill, my JEOL also checks the
LN2, which increases the N2 flow in the outgas tube; I assume Varian and
Bruker instruments do that, too.
--Bill
William Thurmes, PhD Chemistry Manager Miyota Development Center of
America (MDCA)
2602 Clover Basin Drive #A Longmont, CO 80503 USA Ph 303.774.2289
Fax 303.772.2193
The contents of this e-mail and any attachments are Miyota Development
Center of America Confidential and Proprietary
From: Robert Peterson
[mailto:peterson_at_mbi.ucla.edu<mailto:peterson_at_mbi.ucla.edu>]
Sent: Friday, August 19, 2016 4:13 PM
To: AMMRL
Subject: Fwd: Fwd: AMMRL: very scary nitrogen fill
Hi everybody,
Thanks to everyone who responded. I've learned a lot from this experience,
and from all the replies.
One thing I learned is that many AMMRLers go on vacation this time of year.
I received about as many out-of-office replies as normal responses. Note to
self: try not to have major problems during the month of August :)
Everyone agreed with me that my problem was caused by an ice blockage of the
nitrogen port. People offered various possible reasons why an ice blockage
might occur. One thing I hadn't really been aware of is that ice sometimes
forms in the nitrogen ports during helium fills. The pressure in the
nitrogen dewar can become very low while helium is filling, and air can
enter. And in fact, I did do a helium fill the week before. So in my case,
that's probably what happened. One person suggested filling nitrogen during
the helium fill to prevent this. I'm not wild about that idea, but I may
start closing off the nitrogen vent port during the helium fill to prevent
air from getting in. Another possible solution is to always fill nitrogen
just before filling helium (which I normally do, but did NOT do the most
recent time I filled helium - another indication that that He fill caused
the problem)
Received on Thu Aug 25 2016 - 14:10:33 MST