I have the luxury of having a friend bring me helium from his liquefier when I need it.
I rarely have to siphon off the snow from the bottom but now and then some unscrupulous user will trash his dewar and the poor fellow has to go through a lot to clean it out. His comments and recommendations are below.
In the old days, when we had 3-on-a match, the last user would have to get the last drop and try not to plug up the transfer line with sludge.
It’s no fun to try to fill a needy magnet with a plugged line…and just good manners to use good technique and a reasonable quality gas.
Here are comments from a supplier…
“The people using low grade helium are causing problems for OTHER people.
The supplier, who has to clean out the crap (and then raise prices) and the other customers that get the dirty dewars before dewars are so bad that they have to be cleaned.
For NMR type magnets there is not a problem other than plugging a transfer tube when hitting the snow at the bottom of a dirty dewar.
For experimental cryostats with capillary tubes like the Quantum Design PPMSs and Squids, a little bit of snow contaminate in the bottom of a helium dewar can put them out of business for weeks.
We use 99.995% called High Purity (HP) by Airgas. Industrial/balloon grade is also listed at 99.995% but the HP is batch tested to be that pure, whereas Industrial could have any amount of impurities in it. We have measured some Industrial grade cylinders at 98.5% helium from various vendors in the past.
Balloon gas these days can't be trusted.
HP is 5% more expensive than Industrial for us.
And yes, bad transfer techniques and operator errors can make things much worse.”
From: Hirschinger, Jerry D [mailto:jerryh56_at_purdue.edu]
Sent: Monday, October 06, 2014 6:12 PM
To: Ammrl_at_ammrl.org
Subject: RE: AMMRL: Helium Gas Specification for Refilling Purpose
Even if there is significant contamination in your supply dewar, impurities can be easily blown off during the precool of the Xfer line by inserting it all the way to the bottom of the dewar. Fully inserting the supply end of the line during precool should therefore be standard procedure during a LHe fill.
All of this worry about contamination in the magnet during a fill is misplaced, IMO. If minor impurities are introduced during a fill, they go immediately to the bottom of the magnet and remain there at LHe temperature doing absolutely nothing! We have magnets which have been at field for 25 years using Grade 4.5 pusher gas, and they’ll quench from vacuum seal failure many years before the LHe tanks fill with contaminants.
Cheers, -Hirsch
Jerry Hirschinger, NMR Instrumentation Specialist
Purdue Interdepartmental NMR Facility
560 Oval Dr. West Lafayette, IN 47907-2084
Office: Wetherill 365A
Phone / Fax: (765) 494-5288 / 494-0239
Cellular: (765) 427-3034
From: Craig Grimmer [mailto:craig.grimmer_at_gmail.com]
Sent: Sunday, October 05, 2014 2:08 AM
To: Charles L. Anderson Ph.D.
Cc: Gudzon, Ana; Matthias Findeisen; Ammrl_at_ammrl.org<mailto:Ammrl_at_ammrl.org>
Subject: Re: AMMRL: Helium Gas Specification for Refilling Purpose
In an environment where one shares delivery dewars with other users at different sites, and where a single dewar is used to fill multiple magnets at the same site, I think that one has a responsibility to make sure that what goes into the dewar as a pressurizing gas doesn't contaminate the remaining liquid helium (as far as possible), and pass that on to the next magnet, or the next user.
Craig.
On 3 October 2014 21:48, Charles L. Anderson Ph.D. <shiulong_at_central.uh.edu<mailto:shiulong_at_central.uh.edu>> wrote:
We use UHP Helium gas from Trigas.
Chuck
Charles L. Anderson, Ph.D.
Manager NMR Facilities Office: 832-842-8862<tel:832-842-8862>
Department of Chemistry Fax: 713-743-2469<tel:713-743-2469>
Science Engineering Research Center (SERC) W5009A
Cell: 281-841-7588<tel:281-841-7588>
University of Houston
Web:nmr-Central.chem.uh.edu<
http://nmr-Central.chem.uh.edu>
Houston, TX 77204-5003
"Anything one man can imagine others can make true"
Jules Verne
-----Original Message-----
From: Gudzon, Ana [mailto:Ana.Gudzon_at_Covidien.com<mailto:Ana.Gudzon_at_Covidien.com>]
Sent: Thursday, October 02, 2014 1:38 PM
To: Matthias Findeisen; Ammrl_at_ammrl.org<mailto:Ammrl_at_ammrl.org>
Subject: RE: AMMRL: Helium Gas Specification for Refilling Purpose
We use zero or 5th grade from Airgas. You can call Airgas and ask for the %
for zero and 5th grade.
-----Original Message-----
From: Matthias Findeisen [mailto:matthias.findeisen_at_uni-leipzig.de<mailto:matthias.findeisen_at_uni-leipzig.de>]
Sent: Thursday, October 02, 2014 5:29 AM
To: Ammrl_at_ammrl.org<mailto:Ammrl_at_ammrl.org>
Subject: AMMRL: Helium Gas Specification for Refilling Purpose
Dear all,
which Helium-Gas Cylinder do you use for refilling the magnet (i.e. to give
slight pressure onto the refill dewar)?
Is the specification of 99.996 % sufficient for this?
Which experiences do you have?
Thanks!
Yours
Matthias Findeisen
Univ- Leipzig/ Germany
Received on Tue Oct 07 2014 - 08:38:27 MST