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Subject: Re: LN2 and NMR
Date: Thu, 29 Jan 2009 15:43:06 -0500
Author: "Norwood, Brad"
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Subject: Re: Eyewash Flushing
Date: Thu, 29 Jan 2009 19:42:15 EST
Author: Jim Kaufman
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Date: Thu, 29 Jan 2009 18:33:16 -0500
Reply-To: List Moderator <ecgrants**At_Symbol_Here**UVM.EDU>
Sender: DCHAS-L Discussion List <DCHAS-L**At_Symbol_Here**LIST.UVM.EDU>
From: List Moderator <ecgrants**At_Symbol_Here**UVM.EDU>
Subject: 3 Re: [DCHAS-L] LN2 and NMR
From: Teresa Arnold
Date: January 29, 2009 4:19:52 PM EST (CA)
Subject: Re: [DCHAS-L] LN2 and NMR
We switched to a Goddard fitting which works great (as long as you
keep a supply of o-rings). The hose we set up was getting kinda worn
out. I was told that a too-fast fill would mess up the inside too
though. I still fill ours in about 20 minutes though.
Teresa Arnold
Biology-Chemistry Lab Coordinator
503.554.2724
tarnold**At_Symbol_Here**georgefox.edu
414 N. Meridian St. Box 6144
Newberg, OR 97132
==
From: "Alnajjar, Mikhail S"
Date: January 29, 2009 5:30:03 PM EST (CA)
Subject: RE: [DCHAS-L] LN2 and NMR
>My vote is for the slow fill.
I agree with Brad. But, if you need to do the refill quickly it is
advisable to monitor the refill carefully because the rubber hose used
in filling will split when least expected.
__________________________________________________
Mikhail Alnajjar, PhD
==
From: Jeff Walton
Date: January 29, 2009 5:50:09 PM EST (CA)
Subject: Re: FW: [DCHAS-L] LN2 and NMR
Hi Anne,
This was forwarded to me by a friend on this list serve.
It is a small threat. You probably should be using braided stainless
steel built for cryogenic purposes (it's non-magnetic) and not rubber
at all. If the hose breaks, it's probably because it is frozen and has
had stress put on it - whether it's from somebody bumping the dewar or
high speed transfer causing vibration. Having said that, we still use
a small piece of rubber it make a last connection and using latex hose
is a common practice. The possibility of a split is, of course, one of
the reasons why you wear goggles during the fill. In the good old
days we would buy foam insulation from the hardware store, the kind
with a slit you slip around hot water pipes, and slip it over the
latex hose, then loosely wrap with tape. This insulates it and if the
hose shatters like a piece of glass, it's contained (probably).
For fill speed, you certainly want to start slowly until the hose
freezes. And even with steel hose, you want to start slowly because
you don't want to hit your LN2 well with a pressure wave. Once liquid
is flowing you can go faster. How fast depends on your magnet. Look in
the magnet manual. On our older lower field Oxford magnets that are
built like tanks, I open it up. On the more delicate high field
instruments we go a bit slower. Our 500 manual says transfer at 5 psi
and the 800 manual says 7 psi. Our LN2 dewars come at 22 psi so on the
500 we choke it back some and on the 800, we bleed the over pressure
down. On the 800, the vendor indicated that it takes longer for the
magnet to settle back down if you transfer at a higher pressure which
means longer before you can take meaningful data.
Hope this helps!
Jeff
--
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) 752-3516 (FAX)
mailto:jhwalton**At_Symbol_Here**ucdavis.edu
NMR Facility: http://www.nmr.ucdavis.edu
CalEPR: http://calepr.ucdavis.edu
Britt Lab: http://brittepr.ucdavis.edu
Biomedical Engineering: http://www.bme.ucdavis.edu/profiles/gradgroupfaculty/walton.html
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