Date: Wed, 3 Sep 2025 21:00:38 +0000
We have been wondering what to do if that scenario happened, and it did over
the weekend ... we have a ~ 235 cu ft helium bag, and boiloff from our 7 NMR
magnets will fill it in about 30 hours. We tried switching our system over
to direct recovery, but the pressure in our helium recovery lines is very
low, and it wasn't enough to produce gas flow compared with the back pressure
in our purification setup. However, we found that an inexpensive diaphragm
pump (~ $600) connected between the bag and our storage cylinders did the
trick. The pump only produces a couple psi in the cylinders, but that is
enough to get through the purifier, and produce near normal amounts of
liquid helium by our standards, about a liter an hour. The pump pictured
empties the bag a bit faster than the magnets fill it, so we only have it
on while we are there to make sure the bag doesn't get completely deflated.
David VanderVelde
Manager, Liquids NMR Facility, Caltech
davidv_at_caltech.edu
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(image/jpeg attachment: diapump.jpg)