Hi all,
No real agreement, but the advice of the majority seems to be: Helium level at maximum (to keep it cold) and N2 at minimum (because of weight). See below.
Thanks to all for the useful comments.
Cedric
Cédric Malveau, PhD
Laboratoire de RMN
Département de Chimie
Université de Montréal
Tél. 514-343-6111 #1966
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Definitely good have it discharged. Move with low levels of cryogens to lessen the weight during the move. That reduces the primary risks of damaging a support rod from a sudden bump or elevation change. I think it's OK to have LHe at ~20%, LN2 could be nearly 0. Fill as soon as the magnet is in place. Other people almost certainly smarter than me on such a question. But that's my understanding of such a move.
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why not to move charged. If there are no ferromagnetic parts too close during the transport (As a rough estimation 1 meter for unshielded and 30 cm for shielded magnets) you should try. There is a risk of course but discharging/recharging is a risk as well. There are numerous examples especially for older 500 MHz Oxford magnets, which never came back to field. Its your decision but if course you can discuss with the spectrometer manufacturer in advance.
Concerning the cryogens: max helium, min nitrogen (because if the weight).
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I believe that helium should be full for discharging.
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Yes, it must be filled to capacity with both helium and nitrogen.
Moving it will accelerate boil off so it must be full.
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we just moved our 400 and 600 deenergized and about half full with both helium and nitrogen. We were told that as long as the coils are covered you should be ok. Obviously the more you have in there the bigger the lifting equipment you need.
Good luck make sure the removal firm you use does not shake it too much.
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I assume you know you will need to have helium level at >85% (ideally 100%) when you discharge the magnet current.
I think all the magnets I know of that were moved cold were pretty full
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We recently moved a 500 and a 300 magnet cold AND charged about 15 miles by road. It was a total success, just a few more grey hairs. The engineer (who was highly sceptical of it having any chance) told us to move them as empty as possible of N2 and as full as possible of He to avoid any mass shifting during transit. I had thought the opposite, that both being completely full would provide a dampening or buffering effect. However, we let the N2 tanks boil down all the way and had the He tanks at 100%. We had spare He waiting in case of a quench but didn't need a drop.
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If magnet is not charged, it is better to move it with minimum Liquid in it, as it does not really matter even if it gets dry, however little Helium in it is good, so that once it is shifted to final place, you can simply fill helium and go ahead for charging.
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My 300 mhz bruker was moved cold. They wanted the helium level above 75% for the move. We also had to have 100L of liquid helium on hand in case it quenched durong the charging phase. Hope you get lots of good answers.
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If it's discharged I wouldn't be too concerned about the filling level. The only thing I could imagine is that there's less room for the cryogens to move around in the dewar, when it's filled to the top. This may be beneficial for the physical stability when moving it around. The suspension of the coils in the dewar is quite fragile. The moving of the cryogens in a half filled dewar may put unwanted horizontal forces on them.
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I moved a 500 cold with Bruker. It's easier to keep a minimum in it. It's easier to hoist off the legs onto the pallet. The magnet can be topped up when you get it into place and start recharging it. Try to keep the magnet as level as possible during the move.
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We moved a live 500MHz magnet a while back (from one room to another).
The advice at the time was move with the liquid He topped off, but with liq. N2 at a low level to minimize the weight and to avoid sloshing around in the N2 container that would create additional mechanical stresses. I suspect that same advice might apply to moving a discharged magnet.
Obviously you will still have to be very gentle to avoid damage to the magnet mounting internals without the shipping restraints installed.
We rented low cost aluminum scaffolding from a local supplier that we erected around the magnet to provide a lift point. We used a non-magnetic chain-fall (from McMaster-Carr) that was hung from aluminum I-beams supported on the corners of the scaffold. This was much cheaper than having the usual non-magnetic tripod or A-frame shipped in.
The legs were detatched then the magnet lowered onto a non-magnetic dolly (with an open base to allow for the round bottom and OVC fittings). Of course all this would be much simpler with a discharged magnet...
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Ideally, not, but don't stress it too much. I did not take care to fill or empty anything when I did. The density of liquid helium is 125 g/l. I don't know how much you magnet holds, but 100 liters is 12.5 kilograms. This is minor compared with the weight of the magnet itself. Liquid nitrogen is 807 g/l and so is more of a concern. You can blow out most of it. You want to keep some liquid (both He and N2) in there so that it is not prohibitively expensive to ramp back up. Fill the magnet with liquid helium before putting the charging stick in to discharge, and when done, move with whatever is left. What you do not want are any sudden bumps or stops because that in principle could break spacing rods. When it is in it's new home, then fill before ramping up.
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Received on Wed Jun 06 2012 - 10:55:30 MST