Joe’s comments are right on - even with a drop plate. We brought down a magnet gracefully, put it in the hall and several days later it blew out through the drop plate. Luckily it was 4 in the morning. The janitor got quite a fright and the hall was filled with mylar snow, but no one got hurt. Either the drop plate iced over or the O-ring on the plate had deteriorated into “glue”, but something happened so that the drop plate did not work as intended.
Caution is warranted. If you have a pumping station you might want to hook it up and at least monitor the pressure in the vacuum jacket and pump if the pressure goes up or pump when unattended. Of course pumping is the opposite of letting He or N2 into the vacuum and it will take longer to warm up.
Good Luck Indeed! We didn’t have it.
Jeff
> On Mar 7, 2018, at 12:01 PM, Joseph Dumais <josephdumais_at_boisestate.edu> wrote:
>
> I would recommend letting the LN2 evaporate and allowing the He boil off to raise from that and purging the LN2 space with N2 gas to prevent condensation and maybe even icing seems very wise. Allowing the He to reach a fairly low level before starting this would also seem helpful. Since you do not want the magnet, any possible damage to the coil is not an issue and having the least amount of cryogens at the time of the actual quench just seems prudent.
>
> One issue that I do not think I have seen mentioned in this thread is that older cryostats may not have the pressure release disc on the vacuum space. If your O-rings have leaked and allowed N2 and other gases to freeze into the vacuum space there is a chance that the dewar space may pressurize as it warms up. As I understand (but only by second hand information) there have been a few dramatic cases of this where the bore tube failed under pressure and lots of super insulation was blow out of the system. Newer systems have a drop plate on them and for a while it was common practice to loosen the flange bolts after the system was at field and under vacuum (only on vertical bore magnets as best as I know) to allow pressure to release at that flange if necessary.
>
> I have heard of people allowing a "burb" of Helium gas into the vacuum space to elevate the boil-off. You can repeat as necessary after you give it a chance to settle out and see what the impact is. Caution and patience is helpful.
>
> That said I have seen this done in a way that I would have been very unhappy with the outcome. I have seen bits blow off the top of the magnet and fly by someone in the room.
>
> My final comment would be that this is not a spectator sport! Limit access to the room to necessary, not interested personnel, lots of people may want to watch when they hear you are going to quench it.
>
> Good Luck
>
> Joe
>
> *******************************
> Joe Dumais, Ph.D.
> Associate Research Professor/Nuclear Magnetic Resonance Spectroscopist
> Boise State University
> College of Arts and Sciences
> Department of Chemistry and Biochemistry
> 1910 University Drive, Boise, Idaho 83725-1520
> (208) 426 4913
> http://chemistry.boisestate.edu/ <http://chemistry.boisestate.edu/>
> *******************************
>
> Sent from my MS Windows PC
>
>
> On Wed, Mar 7, 2018 at 9:38 AM, Hirschinger, Jerry D <jerryh56_at_purdue.edu <mailto:jerryh56_at_purdue.edu>> wrote:
> Sorry Phil, but I beg to differ. Cracking the vacuum on a live magnet is NOT a good idea. Loss of vacuum results in masses of water condensing on the outside. Quenching will freeze that water, and can interfere with operation of the quench relief valves. Blocking the exhaust of a quenching magnet makes a bomb.
>
> To speed up a dry quench, you must blow out the cryogens through a siphon tube. Thick-walled polyethylene tubing can reach the bottom of the LN2 can. The LHe transfer line, or the magnet L-tube can reach the bottom of the LHe can by way of the siphon cone. If they are sealed well, the boiloff pressure will push out the liquid, or you can use the appropriate pusher gas. Do NOT use N2 to push out LHe.
>
> After the magnet quenches, then the vacuum can be released, but beware this will make a great wet mess in the lab from water condensation. The mess can be avoided by warming the magnet, using the same siphon tubes to inject warm gas into the bottom of the cans. Again, do NOT use N2 to warm the LHe can until the magnet temperature is above 77K.
>
> Be SAFE out there! -Hirsch
> Jerry Hirschinger, NMR Instrumentation Specialist
> Purdue Interdepartmental NMR Facility
> 560 Oval Dr. West Lafayette, IN 47907-2084
> Office: Wetherill 365A
> Phone / Fax: (765) 494-5288 <tel:%28765%29%20494-5288> / 494-0239
> Cellular: (765) 427-3034 <tel:%28765%29%20427-3034>
>
>
>
> -----Original Message-----
> From: Philip Dennison [mailto:dennison_at_uci.edu <mailto:dennison_at_uci.edu>]
> Sent: Tuesday, March 6, 2018 10:06 PM
> To: Lingchao Zhu <lzhu_at_chem.wisc.edu <mailto:lzhu_at_chem.wisc.edu>>; ammrl <ammrl_at_ammrl.org <mailto:ammrl_at_ammrl.org>>
> Subject: Re: AMMRL: quench a horizontal magnet
>
> On 20180306 11:41, Lingchao Zhu wrote:
> > Hello AMMRL,
> >
> > We have an old Thermo LTQ FT Ultra Mass spectrometer waiting for its
> > retirement. *(Model: Finnigan LTQ FT Serial No: SN06036F)* It has a
> > horizontal Oxford magnet*(Part No: AJH0280)* and we are not going to
> > reuse this magnet. We don't have any magnet book or charging rod of it.
> > According to the student in the lab, it has 7T magnetic field.
> >
> > Without too much information from the lab, we decide to dry-quench
> > this magnet, meaning we will let the cryogen boiloff itself to induce
> > a quench. I have following questions to ask and would appreciate any
> > input from AMMRL community:
> >
> > 1. Should we let the liquid nitrogen go dry completely first and then
> > waiting for all liquid helium boiloff? Or we need to keep filling
> > liquid nitrogen until the liquid helium level is low then stop filling
> > liquid nitrogen? Which way is safer?
> > 2. Please see the attached photo for top part of this magnet. It has
> > helium exhaust port built on top of it so when quench happens all the
> > helium gas will blow out through this big pipe. Anything we need to
> > check before the quench happens?
> > 3. Any other important notes before the quench? We will definitely
> > block the lab room when the cryogen is low.
> >
> > Thank you.
> >
> > Lingchao
> >
>
> Hi Lingchao,
>
> Do you have the ability to open the vacuum space of the magnet? If you can do that when the cryogens get low, a quench will happen fairly quickly. That way you can have some control over the quench timing.
>
> If you have anyone interested in re-using the magnet, then dry nitrogen gas is the best way, otherwise it won't matter.
>
> Regards,
>
> Phil.
>
>
> --
> Dr Phil Dennison
> NMR Facility Director (949)824-6010 <tel:%28949%29824-6010> (office)
> Department of Chemistry (949)824-5649 <tel:%28949%29824-5649> (lab)
> University of California (949)824-8571 <tel:%28949%29824-8571> (fax)
> Irvine, CA 92697-2025 dennison_at_uci.edu <mailto:dennison_at_uci.edu>
> USA
>
>
Jeffrey H. Walton
UC Davis NMR Facility, 4303 Tupper Hall
Biomedical Engineering Graduate Group
One Shields Ave.
University of California
Davis, CA 95616
(530) 752-7794 (office)
(530) 752-6480 (MS1-D lab)
(530) 754-0133 (CalEPR, Chem 76)
(530) 754-8238 (Chem 93 lab)
(530) 754-6633 (CMGI)
(530) 752-8520 (FAX)
mailto:jhwalton_at_ucdavis.edu
NMR Facility: http://www.nmr.ucdavis.edu
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Biomedical Engineering: http://bme.ucdavis.edu/people/graduate-group-faculty/grad-group-profiles/jeffrey-walton/ <http://bme.ucdavis.edu/people/graduate-group-faculty/grad-group-profiles/jeffrey-walton/>
Received on Fri Mar 09 2018 - 06:08:08 MST