Ken,
We had this problem last year. I didn't think it was an ice block,
because I could see a plume coming out of the exhaust port on the prodigy
LN2 dewar. However, it turns out there was a large plug of ice further
down in the metal tube that connects to the exhaust port on that dewar -
although it wasn't completely blocked, it was blocked enough that the high
pressure during the fill was forcing LN2 into the probe and out the heater
on the probe.
To fix this, you have to cut that metal wire on the clamp so that you
can pull the assembly out of the LN2 dewar and then remove the ice block(s)
from the little L-shaped metal tubes connected to the two ports. After
doing this, we haven't had any problems with LN2 fills for almost a year.
Before this, we would have all sorts of trouble with the Prodigy
spontaneously warming up after a LN2 fill long before we started seeing the
LN2 coming out of the probe heater exhaust port. It turns out that was all
due to the high pressure in the dewar from the (partial) ice block on the
exhaust port.
-Scott
On Wed, Jun 7, 2023 at 8:21 AM Kenneth Sharp-Knott <kknott_at_vt.edu> wrote:
> Noticing today that there is LN2 gas coming out of the probe heater
> exhaust outlet and out of the front of the prodigy unit during the refill.
> I haven't observed this before.
>
> We opened up the LN2 dewar and the inlet and outlet stems are nearly the
> same length. I don't recall, but I'm wonder if perhaps the inlet is
> supposed to have tubing or something extending deeper into the dewar?
>
> There are no blockages that I can observe.
>
>
>
--
Dr. Scott Burt
Professor
NMR Facility Manager
Department of Chemistry and Biochemistry
Brigham Young University
C414 BNSN / C008A BNSN
Provo, Utah 84602-5700
Phone: (801) 422-2404
Fax: (801) 422-0153
chembio.byu.edu/nmr-facility/
email: scott_burt_at_byu.edu
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Received on Wed Jun 07 2023 - 08:54:28 MST