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).
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><mailto:peterson_at_mbi.ucla.edu>
To:
AMMRL <ammrl_at_ammrl.org><mailto: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><mailto:peterson_at_mbi.ucla.edu>
To:
AMMRL <ammrl_at_ammrl.org><mailto: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<mailto:peterson_at_mbi.ucla.edu>
-----------------------------------------------
Received on Wed Aug 24 2016 - 09:13:48 MST