In our experience, "dry shipper" dewars will "fail" for two reasons:
1) the vacuum gets compromized
2) the "sponge" that soaks up the liquid nitrogen gets contaminated with
water
Hot and cold cycling can cause the vacuum pump-out valve (that
sticky-out thingy that always seems to be in the way) to leak. This
includes spilling liquid nitrogen on the valve while filling the dewar!
Once the vacuum starts to go, you will notice the outside of the dewar
is cool or even icy to the touch, and this further weakens the valve
seal. Makes one wonder why we bother with a valve, until, of course,
you actually do need to pump it down. We have rescued a couple of user
dewars over the years by pumping them down. Doesn't always work, but
sometimes it does. Obtaining the fitting for the port is the tricky
part. We got ours from here:
http://www.cryocomp.com/vacuum_valves/product.php?id=50
The contaminated sponge problem is different, and depends on what kind
of "sponge" you have. Most modern dewars use a zeolite, which is a
porous mineral. The name literally means "boiling stone", which I think
reflects how hot you have to get it to drive off the water. Other types
of "sponge", such as cotton wool can be easier. However, if you are
patient, there is nothing quite like a very large volume of reasonably
dry air blowing over something wet to get it to dry out. The boil off
gas from a liquid N2 tank, flowing through a warm dewar for days to
weeks should eventually dry it out completely. You can keep weighing it
to monitor the progress.
And, as always, there is no substitute for testing your shipping dewar
by prepping it as you would for your precious samples, and then putting
a thermocouple in it and verifying that it actually does last for 2
weeks or more without the temperature rising about that of liquid nitrogen.
-James Holton
MAD Scientist
On 7/17/2013 7:33 AM, Mark J van Raaij wrote:
I heard or read (don't remember where) that repeated warming/cooling cycles are what can
make the dewars less efficient and can "break" them.
So we keep them always with liquid nitrogen, filling them every week if we can.
But we are lucky that Madrid has low humidity most of the year. And perhaps our
liquid nitrogen supply is also relatively dry (I don't know this), because we
haven't had too much problems with icing.
Given your advice, maybe we should dry our dewars once or twice a year at least.
Mark J van Raaij
Lab 20B
Dpto de Estructura de Macromoleculas
Centro Nacional de Biotecnologia - CSIC
c/Darwin 3
E-28049 Madrid, Spain
tel. (+34) 91 585 4616
http://www.cnb.csic.es/~mjvanraaij
On 17 Jul 2013, at 16:25, Johan Turkenburg wrote:
We put a supply line of compressed air (not sure how dry this is) in the dewar
to wam it up and dry it out. We leave this running overnight, and this seems to
result in the dewars being dry enough for later use. We haver never bothered to
weight the dewars before and after use etc, so can't comment on how well this
really dries the dewars. Icing seems in our case more dependent on manipulation
of the samples and the pucks (we think unipucks cause more problems than pucks
that hold the pin in a vial, but can't prove that). And maybe on how clean the
LN2 is in the sample changer dewars (at home and at the synchrotron).
Johan
On 17 July 2013 12:34, Phil Evans <p...@mrc-lmb.cam.ac.uk> wrote:
In response I felt I had to post the low-tech version (not mine)
Phil
<IMG_0694.jpeg>
On 16 Jul 2013, at 11:57, Edward Lowe <edward.l...@bioch.ox.ac.uk> wrote:
At Elspeth's request, here's a link to a picture of the rack we use for
drying out shipping dewars.
https://www.dropbox.com/s/8ber2iikra9x73y/2013-02-21%2013.39.38.JPG
Very simple and both we and the Lea group here have found it to make a
huge difference the the effectiveness and longevity of our dewars.
Ed.
--
Dr. E.D. Lowe
Department of Biochemistry
University of Oxford
South Parks Road
Oxford, UK
OX1 3QU
e:edward.l...@bioch.ox.ac.uk
t: +44 (0) 1865 613288
f: +44 (0) 1865 613201
On 12/07/2013 14:27, "Edward Snell" <esn...@hwi.buffalo.edu> wrote:
Ditto - I was always impressed with the contraption in the Garman lab
which, if I remember correctly, is made of a thick block of wood and some
plumbing pipes. It is designed to hold empty open Dewars inverted so they
could dry.
Edward Snell Ph.D.
Assistant Prof. Department of Structural Biology, SUNY Buffalo,
Senior Scientist, Hauptman-Woodward Medical Research Institute
700 Ellicott Street, Buffalo, NY 14203-1102
Phone: (716) 898 8631 Fax: (716) 898 8660
Skype: eddie.snell Email: esn...@hwi.buffalo.edu
Telepathy: 42.2 GHz
Heisenberg was probably here!
-----Original Message-----
From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of
Ginell, Stephan L.
Sent: Friday, July 12, 2013 12:45 AM
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] frosted crystals during storage in pucks
My experience with xtals frosting in LN2 either in a dewar, while
freezing, or in pucks, has been because the LN2 was contaminated with ice
crystals The fog you see above your dewar when freezing xtals is frozen
water vapor...it will fall and collect in the LN2 and also deposit on the
xtals. Dewars filled with recycled LN2 get contaminated with ice. Dewars
dried upside down allow the cold gas to flow out and warm moist air to
flow in and the water to condense inside the dewar (basic physics). To
dry shipping dewars keep up right while warming.
Steve
Sent from my iPad
On Jul 11, 2013, at 5:25 PM, "Nathaniel Clark"
<nathanielcl...@gmail.com<mailto:nathanielcl...@gmail.com>> wrote:
At our last synchrotron trip, the beamline staff suggested that the
problem was due to moisture accumulation in the dry shipper. They
recommended storing them inverted (for a few weeks, if I recall), and/or
putting a supply of dry air in the dewer. Haven't tried it yet!
Nat
On Thu, Jul 11, 2013 at 5:08 PM, <Rain Field>
<rainfiel...@163.com<mailto:rainfiel...@163.com>> wrote:
Hi All,
We found if the crystals are storaged in pucks for 3-4 days in shipping
dewar (with liquid nitrogen), they are almost frosted.
Although I can wash them with liquid nitrogen, but it's not convenient to
do that for each crystals.
I doubt it's because the humid air in North West America.
Does anyone has an idea how to avoid this?
Thank you!
--
Dr. Johan P. Turkenburg X-ray facilities manager
York Structural Biology Laboratory
University of York Phone (+) 44 1904 328251
York YO10 5DD UK Fax (+) 44 1904 328266
Note new email address johan.turkenb...@york.ac.uk
