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]
*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).
Also, Doug Lyons from Bruker said that the internal welds on Magnex magnets
result in very narrow spaces in the nitrogen ports. This makes ice
blockages more likely than on other types of magnets. He also asked if the
magnet's nitrogen dewar was empty or very low. He said if you fill nitrogen
at the normal rate when the magnet's dewar is very low, you can build very
high pressure in the dewar. In my case, I don't think that was the reason,
but it's something to keep in mind.
Several people suggested that my nitrogen wasn't pure (or that it wasn't
nitrogen). I don't think that was the case - we have a large nitrogen
storage tank that we use to fill our dewars. If there was something wrong
with the bulk nitrogen, I'm sure other people would have had problems.
There were also several theories as to what caused the strange cycling
behavior. I'd love to know what caused it, but I'm afraid I'll have to live
with uncertainty there.
Several people wondered about the vacuum seals and how well the magnet has
been maintained. I think everything is OK there. The behavior of the magnet
(hold times and flow rates) has not changed at all in the 20 years since it
was installed. This is the first unusual incident I've ever seen.
Many people cautioned me to carefully watch the boiloff rates. It's only
been a week, but so far the boiloff and everything else is completely
normal. The nitrogen fill this week went smoothly. Hopefully nothing was
damaged and this will be an isolated incident.
Thanks again to everyone.
-Robert
-------- Forwarded Message --------
*Subject: *
Fwd: very scary nitrogen fill
*Date: *
Wed, 10 Aug 2016 09:16:58 -0700
*From: *
Robert Peterson <peterson_at_mbi.ucla.edu> <peterson_at_mbi.ucla.edu>
*To: *
AMMRL <ammrl_at_ammrl.org> <ammrl_at_ammrl.org>
Dear group,
OK, I think I mostly know what happened. There was actually a partial
blockage on the vent side. At the time that I wrote, it had just happened
and the radiator that I have on the vent side was still frozen from the
fill, so I hadn't actually checked whether that side was blocked. And
nitrogen had been shooting out that side very hard all through the fill so
I assumed it was clear.
But now it's clear that it was partly blocked during the fill. That must
have led to pressure building up inside the nitrogen dewar. I cleared it
and refilled nitrogen this morning. Everything behaved completely normally,
so hopefully it will be OK.
Two things I don't understand though: the first is the cycling of the
pressure when I removed the filling hose from the fill port yesterday. It
was truly amazing to see. It cycled between almost no flow at all to
erupting like a geyser over a period of about 20 seconds, and continued for
6-8 cycles before it started to wind down.
The other thing is the change in sound that I heard during the fill
yesterday. In retrospect it really seems like that could have been the
blockage forming. Is that possible?
Anyway, I will pay closer attention to sound changes in the future.
Thanks in advance for any information.
-Robert
-------- Forwarded Message --------
*Subject: *
very scary nitrogen fill
*Date: *
Tue, 09 Aug 2016 15:56:48 -0700
*From: *
Robert Peterson <peterson_at_mbi.ucla.edu> <peterson_at_mbi.ucla.edu>
*To: *
AMMRL <ammrl_at_ammrl.org> <ammrl_at_ammrl.org>
Dear group,
I just had a very disturbing experience just after filling nitrogen. The
system is a Bruker 600 - Magnex magnet, installed in 1996.
I filled nitrogen, and it took much longer than usual. It took about 90
minutes, while it usually takes ~40. Also, during the fill there was a
change in the sound the fill made - it suddenly became louder and higher.
The fill did finish eventually (liquid came out). After it finished, there
was a very strong outflow from the vent port - almost like I was still
filling. After it had gone on like this for a few minutes, I double checked
to make sure the tank was closed (it was).
(The magnet has 3 nitrogen ports. One is occupied by the nitrogen sensor,
and the other two are used for filling and venting during the fill.)
After a few minutes (while it was still venting like crazy), I removed the
filling hose from the magnet: nitrogen came blasting out harder and harder
until *liquid* nitrogen was blasting out so hard it was hitting the ceiling
5 feet above and splashing down on me. Then it gradually calmed down until
only gas was coming out relatively slowly. Then the pressure got higher and
higher until again liquid was shooting out. The full cycle took maybe 20
seconds. This continued for 2-3 minutes. After maybe 6 or 8 of these cycles
it started getting less intense and a few minutes later it had stopped. 10
minutes later it seemed completely normal.
Both of my open nitrogen ports are clear. Nothing was different with my
nitrogen dewar (low pressure - 22psi). The magnet is still a magnet, and
the lock was stable even while the nitrogen was blasting out.
Does anyone know what could cause this? I will post a summary or an
explanation.
thanks,
-Robert
--
-----------------------------------------------
Robert Peterson, Ph.D.
Facility Manager - NMR Technology Center
UCLA-DOE Institute for Genomics and Proteomics
UCLA Dept. of Chemistry and Biochemistry
phone: (310)825-1816
fax: (310)825-0982
peterson_at_mbi.ucla.edu
-----------------------------------------------
Received on Tue Aug 23 2016 - 06:59:39 MST