Thank you to everyone who responded.
I guess my description wasn't very clear and I caused some
confusion/concern, let me quickly clarify.
I mentioned using rigid lines to fill the liquid Nitrogen. The lines are
L-shaped and fit inside the Nitrogen fill ports. One of the rigid lines is
long enough to go almost to the bottom of the nitrogen vessel in the magnet.
The long end is connected to either a rubber hose or a stainless-steel fill
line attached to the Nitrogen dewar. The other line is short and is used to
vent the system to either the environment or an overflow dewar. I apologize
that I gave the impression that this is a closed system, I can see why some
of you were very concerned, I would be as well. If you have the Oxford
magnet instruction manual (200/54 & 300/54 Superconducting Magnet System:
Assembly and Commissioning Manual - Issue A), on page 10-2 you will see the
instructions for Liquid Nitrogen Top-Up that I was told was the absolute way
to fill the magnet.
Our fill method is identical to what many of you are using...the 22-psi
dewar and the rubber hose and venting it with a shorter hose on the other
end. However, some do use the method described in my original e-mail and
have never had a problem.
As for causing damage to the internal Nitrogen vessel using the rubber hose
method, no one had experienced this problem.
Thanks again,
Adrienne
*********
Original e-mail:
_____
> From: Hoeglund, Adrienne [mailto:AHoeglund_at_aoc-resins.com]
> Sent: Monday, February 28, 2005 2:15 PM
> To: AMMRL
> Subject: Nitrogen Fill Question
Hello. Last week I was very involved in a lively conversation concerning
proper Nitrogen fill techniques and determined that there are several
different methods for properly filling the magnet. I was wondering, for
those of you filling a 300 MHz spectrometer, with an Oxford magnet, what
fill technique do you use?
Here is what I was told is the absolute proper way I should be doing it. I
would like some input and/or comparisons to your methods.
1. Lower the pressure in the Nitrogen dewar to no more than 10 psi.
2. Place the two rigid transfer lines in the magnet and begin the fill
slowly.
3. Continue filling until the magnet is full.
4. Allow the system to boil-off for about 30-minutes and then top off the
system.
5. Remove the rigid tubes and put everything up.
>From what I was told in my conversation last week, the technique we were
using could have ruptured the Nitrogen vessel and damaged the magnet.
However, with this new technique I can't tell that liquid is being
transferred, the pressure in the Nitrogen dewar keeps dropping as the fill
is progressing and, I just stopped the fill and rather than filling the
magnet, the Nitrogen level has dropped a centimeter.
>From what I can tell, the assumption is made that there is a constant
pressure of gas pushing the liquid Nitrogen like there is for the helium.
And, the dewars that we get for Nitrogen, that isn't going to work.
Therefore, I would be interested in knowing if you do the fill as described
above or if you have some other technique. If you do use the above
technique, please fill me in on the details.
If there is interest, I will post a summary. If you don't want your
response posted, please let me know that as well.
Thank you in advance for your input.
Adrienne
Adrienne B. Hoeglund
NMR Specialist
AOC, LLC.
950 Highway 57 East
Collierville, TN 38017
(901) 854-2800 ext. 532 - work
(901) 853-1582 - fax
www.aoc-resins.com
Received on Mon Mar 14 2005 - 08:28:40 MST