Re: Short "shelf life" of high pressure LN for SEM EDX system?

On Mon, 15 May 2006 07:34:59 -0400, waltd@xxxxxxxxx wrote:

I have had a LN cooled EDX system for 2-1/2 years and recently the time
it takes for my storage bottle to evaporate has shrunken drastically. I
get LN delivered in 306# tanks (approx 5 ft high x 2 ft dia). Pressure
relief valve is always between 235 and 350 depending on the tank. Tank
is different each time (supplier has many tanks).

For 2 years, I had gotten between 18 and 21 days out of a tank. The
limit is mostly evaporative loss as I only draw about 15 liters a week
to keep the EDX dewar filled. Starting about 4 months ago, I started
getting 11 days from a full bottle (once), then 7 or 8 days ( a few
times). Now I've had one fill that lasted 3 days and the latest 6 days.
What life does anyone out there get from these bottles? I'm thinking the
scale at the filling plant is defective or someone is punching in the
wrong tare. At $100 per fill I'd like to get my meager 40 liters for my
scope. All feedback greatly appreciated.

So you are talking about problems with the delivery Dewar? Not the
EDS Deway.

The large tanks have float indicators to show if they are full or at
some other level. Do you have this on the tanks you get? Make sure
they are full. It would be "normal" for one tank to lose LN2 over a
short period of time if the vacuum and insulation went bad. But to
lose LN2 using different Dewars is quite odd.

What kind of Dewar are you getting? The stainless steel units work
very well. Life of a fill I typically get with a 50L unit is about
two weeks.


Gary Gaugler, Ph.D.
Microtechnics, Inc.
Granite Bay, CA 95746
916.791.8191
gary@microtechnics dot com
.

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