Date: Thu, 29 Jan 2009 18:33:16 -0500
Reply-To: List Moderator <ecgrants**At_Symbol_Here**UVM.EDU>
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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


              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!


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)
NMR Facility:
Britt Lab:
Biomedical Engineering:

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