Re: A Cautionary Tale
Jim Breeyear (jbreeyea@zoo.uvm.edu)
Thu, 01 May 1997 08:32:13 -0700
Jeff Walton wrote:
>
> Rich is right. There was a case similar to this at one of my prior stops
> where I was a post-doc. They had a leak detector with a diffusion pump and
> LN2 trap. They pumped down the magnet once a week. They were able to
> monitor the pressure increase each week. They took an embarassingly long
> time to bring the magnet down and replace the O-rings, but it never
> quenched. Please note that O-rings are not the only place a leak can
> occur. Now that the magnet is down, I would do a complete leak check and
> consider replacing the O-rings even if you don't find a leak there.
>
> Also, as far as I know, there's nothing you can do to stop a quench. Just
> leave the room and pray your magnet survives. Hope this one did.
>
> Good Luck!
>
> Jeff
>
> Jeffrey H. Walton
> UCD NMR Facility
> University of California
> Davis, CA 95616
> (916) 752-7794 (office)
> (916) 754-9064 (lab)
> (916) 752-3516 (FAX)
> jhwalton@ucdavis.edu
> NMR Facility URL http://www.nmr.ucdavis.edu
Hi,
After having experienced a few "surprise quenches" I also agree that
there isnt much one can do when the magnet vacuum is starting to go soft
except put as much helium in as possible and make preparations to bring
it down as required. Take it apart and clean it and repalce the getter
and o-rings completely. I have flow gauges on both magnets and watch
them frequently, making allowances for changes in the weather. One never
knows when his turn is up to sweat out a quench. I caused one quench by
leaving the room when filling with nitrogen. It overflowed and froze the
bottom o-ring. Fortunately I have a power supply. I am going to "knock
on wood" after this message. Why do we knock on wood?
--
=======================================
Jim Breeyear Manager Inst. Lab.
Chemistry Dept Cook Building
Univ. of Vermont
Burlington, Vt. 05405
Tel:802-656-0196