Hi Luke,
I agree with what Mike and Sameer said. I'm also curious about your
setup. You said your helium exhaust ports are "connected to a copper
header line via manifold and long flexible whip". How thin is that
piece? Back pressure on the magnet during fills is a huge problem -
especially at the end of the fill. I think that anything smaller than 1"
would cause big problems during fills.
For our piping manifolds, we basically copied Yale's design
(
https://cbic.yale.edu/about-us/helium-recovery ), except that we used 2"
diameter flexible tubing (on the fill side) to connect to our piping.
Eric Paulson advised me to do that. They used 1" diameter flexible
tubing and he thought bigger would be better. (We do actually have one
magnet that has a short section of 1" flexible tubing on the fill
exhaust and it hasn't caused any problems, so maybe 1" is enough.)
We have modified flow meters installed in the piping manifold (just like
Yale's setup), but we also have pressure gauges. I substituted the
original floats with black corks in the flow meters, and they work well
to indicate when the magnet is full (the corks shoot to the top). But
there's an even better indicator than that: I've found the pressure
gauges to be the most useful tool to both indicate when the fill is done
and to avoid overpressurizing the magnet at the beginning of the fill.
When I was first doing fills, I almost quenched magnets two or three
times (I actually popped quench valves). It always happened when the
magnet got full and I didn't stop the flow of helium or reduce the
pressure in time. Then I realized that the pressure gauge on the wall
was extremely useful, and I now mostly pay attention to that one rather
than to the one on the dewar. The one on the wall (on the piping
manifold) is a better indicator of what the magnet pressure is. I've
found that as long as I keep the pressure gauge on the wall from going
above 1PSI, I don't pop any quench valves. My transfer line has a valve
that controls the flow, and I open and close that valve to control the
flow and the pressure.
Just to emphasize what a powerful tool the transfer line with shutoff
valve is: I've gotten pretty obsessive about not wasting helium. So when
I insert the transfer line into the dewar before starting the fill, I
try not to vent any helium at all. I let the dewar pressure get as high
as 6PSI. When liquid comes out, I stop the flow and connect it to the
fill lance already in the magnet (my transfer lines are in two pieces).
Then, without venting the dewar, I open the valve slightly and watch the
pressure gauge on the wall like a hawk. By opening and closing the
valve, I very carefully prevent the gauge on the wall from ever going=
over 1PSI. It takes about 5 minutes, but eventually the dewar pressure
gets low enough that I can safely open the valve all the way. Then I use
either the pressure builder or a helium cylinder to pressurize the dewar.
(I wouldn't necessarily recommend this approach to everyone, but I've
gotten very good at it)
When the fill is nearing completion, I watch the pressure gauge and the
flow meter carefully (with my hand on the shutoff valve). As the magnet
becomes full, both shoot up quickly and I shut the flow off. If you
don't have a transfer line with a shutoff valve, I can't recommend
strongly enough that you get one. You can almost instantly stop the flow
of helium. Then the magnet is safe and you don't have to rush getting
the other side out of the magnet. I consider a transfer line with a
shutoff valve and a pressure gauge connected to the piping to be the two
indispensable tools for doing magnet fills into piping. I'd be terrified
to do a fill without them.
I think I've won the prize for lengthiest reply :)
Let me know if any of it doesn't make sense.
-Robert
--
-----------------------------------------------
Robert Peterson, Ph.D.
Facility Manager - NMR Technology Center
UCLA-DOE Institute for Genomics and Proteomics
UCLA Dept. of Chemistry and Biochemistry
phone: (310)825-1816
fax: (310)825-0982
peterson_at_mbi.ucla.edu
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Received on Fri Apr 18 2025 - 16:55:16 MST