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Dear AMMRLers,
I indirectly received the message below from someone who was pretty
embarrassed about having used the wrong gas to pressurize the storage
dewar for helium fills. I thought I would relate my experience with
this sort of thing. Quite a number of years ago, I found that the
people working for me had been using nitrogen gas. I have no idea how
long this had been going on or how it happened that we ended up with
nitrogen rather than helium on the cart we use for fills. Amazingly, we
seemed to have not observed any ill effects from this. I thought about
it and decided that if you really did your fills correctly, you could
get away with this, because none of the gas should enter the transfer
line, and if the line is sufficiently above the bottom of the storage
dewar, any condensed nitrogen would not be pushed into the transfer
line. At any rate, we did later de-energize a couple of the solenoids
to move them to a new building. There was no problem whatsoever with
putting in the charging rods, so if there was icing from the nitrogen,
it was not substantial. (Of course, it is possible that the tank had
just been put on the cart when I noticed it and was never used, but I
always presumed it had been used.)
This leads me to another question. I once had a mass spec service
person tell us that we should use ultra-high purity helium (UHP,
99.999%) for the liquid helium transfer into an FT-MS solenoid. I
thought he was crazy, but I supppose it is possible that it would be
better for that particular magnet. Do any of you use UHP helium gas for
transfers? We certainly do not.
Jane Strouse
Message received:
________________________________________________________________________
_______
Dear Spinners,
First of all, happy holiday season!!!
I have been a passive observer and certainly taking advantages of the
fruitful discussions at AMMRL. Here is a story that I feel I can use to
contribute to the community. I am very much embarrassed in making such
mistake, as you can see I am even hiding my name, but I still want to
post it, so everyone could learn something from it.
I have been filling liquid helium to my 400 MHz magnet by myself and for
the past two years I thought that I have been using helium gas to
pressurize the tank (well, read the label before using it). Just a few
days ago, I found that it had been argon gas all along. Before using
this gas cylinder, there had been no problem doing it and after
switching to the tank, I started experiencing technical problems and I
blamed the liquid helium supplier and moisture in the air. Here were
the problems: (1) the liquid helium inlet (on the magnet side) seemed to
be "ice" blocked, (2) it took from one to two hours to fill it, and (3)
at the end of the filling process, it was extremely difficult to pull
out the transfer tube (somehow the tube got stuck somewhere in the
system on the magnet side and especially on the liquid helium tank side
- I even destroyed one of my transfer tubes to pull it out). Of course
the root of the problems is that the argon gas solidified in the system.
Just last week, I found the mistake and switched to helium gas;
everything goes back to normal now.
So, what can we benefit from such odd experience? Although some might
think that there are other factors to consider, from the experience I
believe that we don't need ultra high purity helium gas at all for the
refilling. A regular grade helium gas will do the job just fine. The
gas I used is almost 100% purity argon and it has been two years. If it
doesn't hurt the magnet this way (in terms of building up alarming level
of solids in the magnet or clogging the system permanently), why we need
to use ultra high purity helium gas? By the way, the boiling point of
argon is about -186 C, oxygen is about -183, and nitrogen is about -195
C.
Anyone cares to shed some more opinions?
>From someone too embarrassed to show his/her name.
________________________________________________________________________
_______
----------------------------------------------------------------------
Dr. Jane Strouse
Director, UCLA Molecular Instrumentation Center
1410 Molecular Sciences Building
Los Angeles, CA 90095-1569
(310)-825-9841 - voice
(310)-825-2280 - fax
strousej@chem.ucla.edu
http://www.mic.ucla.edu
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Dear AMMRLers,
I indirectly received the =
message
below from someone who was pretty embarrassed about having used the =
wrong gas
to pressurize the storage dewar for helium fills. I thought I =
would
relate my experience with this sort of thing. Quite a number of =
years
ago, I found that the people working for me had been using nitrogen =
gas.
I have no idea how long this had been going on or how it happened that =
we ended
up with nitrogen rather than helium on the cart we use for fills. =
Amazingly,
we seemed to have not observed any ill effects from this. I =
thought about
it and decided that if you really did your fills correctly, you could =
get away
with this, because none of the gas should enter the transfer line, and =
if the
line is sufficiently above the bottom of the storage dewar, any =
condensed
nitrogen would not be pushed into the transfer line. At any rate, =
we did
later de-energize a couple of the solenoids to move them to a new =
building.
There was no problem whatsoever with putting in the charging rods, so if =
there
was icing from the nitrogen, it was not substantial. (Of course, =
it is
possible that the tank had just been put on the cart when I noticed it =
and was
never used, but I always presumed it had been used.) =
This leads me to another
question. I once had a mass spec service person tell us that we =
should
use ultra-high purity helium (UHP, 99.999%) for the liquid helium =
transfer into
an FT-MS solenoid. I thought he was crazy, but I supppose it is =
possible
that it would be better for that particular magnet. Do any of you =
use UHP
helium gas for transfers? We certainly do not.
Jane Strouse
Message received:
______________________________________________________=
_________________________
Dear Spinners,
First of all, happy holiday season!!!
I have been a passive observer and certainly taking advantages =
of the
fruitful discussions at AMMRL. Here is a story that I feel I can =
use to
contribute to the community. I am very much embarrassed in making =
such
mistake, as you can see I am even hiding my name, but I still want to =
post it,
so everyone could learn something from it.
I have been filling liquid helium to my 400 MHz magnet by myself =
and
for the past two years I thought that I have been using helium gas to
pressurize the tank (well, read the label before using it). Just a =
few
days ago, I found that it had been argon gas all along. Before =
using this
gas cylinder, there had been no problem doing it and after switching to =
the
tank, I started experiencing technical problems and I blamed the liquid =
helium
supplier and moisture in the air. Here were the problems: (1) the =
liquid
helium inlet (on the magnet side) seemed to be “ice” =
blocked, (2)
it took from one to two hours to fill it, and (3) at the end of the =
filling
process, it was extremely difficult to pull out the transfer tube =
(somehow the
tube got stuck somewhere in the system on the magnet side and especially =
on the
liquid helium tank side - I even destroyed one of my transfer tubes to =
pull it
out). Of course the root of the problems is that the argon gas =
solidified
in the system. Just last week, I found the mistake and switched to =
helium
gas; everything goes back to normal now.
So, what can we benefit from such odd experience? Although =
some
might think that there are other factors to consider, from the =
experience I
believe that we don’t need ultra high purity helium gas at all for =
the
refilling. A regular grade helium gas will do the job just fine.
The gas I used is almost 100% purity argon and it has been two =
years.
If it doesn’t hurt the magnet this way (in terms of building =
up
alarming level of solids in the magnet or clogging the system =
permanently), why
we need to use ultra high purity helium gas? By the way, the =
boiling point
of argon is about -186 C, oxygen is about -183, and nitrogen is about =
-195 C.
Anyone cares to shed some more opinions?
From someone too embarrassed to show his/her =
name.
______________________________________________________=
_________________________
------------------------------------------------------=
----------------
Dr. Jane Strouse
Director, UCLA Molecular Instrumentation =
Center
1410 Molecular Sciences Building
Los Angeles, CA 90095-1569
(310)-825-9841 - voice
(310)-825-2280 - fax
strousej@chem.ucla.edu<=
/font>
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