> Dear Michael,
>

Usually the liquid nitrogen tanks are isolated through a vacuum chamber.This
chamber should be reevacuated. Our tanks have a ventil for that.
That could be one reason for which your N2 consumption increased over the
years.
You need also a special adaptor to reevacuate the chamber.

Cheers,

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Dr. Ana-Voica Bojar
Institut für Geologie u. Palaeontologie
Karl-Franzens University
Graz, Austria