Dear Jose,

We have a similar Optima-Isocarb in use and employ a liquid nitrogen level
sensor/filler (as in your option number 2).  It fills the small open dewar
on the mass spec from a 160 liter dewar automaticlaly, and works fine.  I
have been tempted to plumb the160 liter dewar of LN2 directly to the cold
finger (your option 1), and let the mass spec control the valve to reach
the temperature, but have never tried it.  I suspect there may be a problem
with too much pressure.  (?)

LN2 level sensors/fillers can be obtained from a variety of sources in the
U.S.  One of them is:

J.C. Controls
1069 Westridge Ave.
Danville, CA
USA  94526
Ph. 510-837-6677
FAX 510-743-0529

They sell controller unis and solenoid valves that are rated for
cryogenics.  Hope this helps.

Bruce
_________________________________________________________
        Bruce H. Vaughn, Stable Isotope Lab
        Institute of Arctic and Alpine Research
        University of Colorado  CB 450
        Boulder, Colorado  80309

        Office: 303-492-7985                 [log in to unmask]
        Lab:  303-492-5495                    FAX: 303-492-6388
_________________________________________________________

>Dear Isogeochemists,
>        At the University of Baja California (Mexico) we are trying to make
>a few modifications to our Optima-Isocarb system in order to make more
>efficient use (and simultaneously get an uninterrupted supply) of liquid
>nitrogen (for cold-fingers in the dual-inlet) during a carrousel run. Our
>system is set in such a way that we have to fill a 32-liter dewar with
>Liquid Nitrogen at the begining of the batch run. This liquid nitrogen is is
>pumped into the cold fingers by means of two independently controlled (by
>software) Charles Austen Pumps.
>        The drawback of this system is that we have to re-fill the 32-L
>dewar in the middle of the batch run. Instead, we would either like to: (1)
>connect the bigger ~160 Lt thermic containers (in which liquid nitrogen is
>supplied) to the cold finger tube-lines or (2), somehow connect the bigger
>container (~160 lt) to the smaller one (32 lt) by means of any sort of
>liquid nitrogen automatic refiller.
>        These options may sound easy to many of you, but at these latitudes
>we do not know of many suppliers for this type of equipment and accesories;
>most of them are abroad. Option-1 could probably be achieved by using
>electrically-driven selenoid valves, but I have no idea what kind of (so
>they would be Ok for operating at LN temp's). Option-2 could probably be
>simple but we do not know the model or company that sells this kind of
>cryogenic accessories.
>        Could anyone of you please suggest alternatives or provide relevant
>information for this case? Your help will be greatly appreciated.
>
>Regards,
>
>Jose Carriquiry
>
>
>
>
>                                   ,,,
>                                  (o o)
>------------------------------oOO--(_)--OOo-----------------------------
>Dr Jose Carriquiry                          . USA MAILING ADDRESS:
>Instituto de Investigaciones Oceanologicas  . 1125 Loma Ave. #144-E099
>Universidad Autonoma de Baja California     . Coronado, CA 92118
>Apdo. Postal # 453                          . USA
>Ensenada, Baja California, c.p. 22,800      .
>Mexico                                      .
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>http://www.ens.uabc.mx/iio/iio.htm
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