We were performing normal 80 day helium fill maintenance on our Oxford magnet for a 300 MHz NMR. During the fill we had 4 separate events where the pressure in the helium dewer became negative relative to the atmosphere and began sucking atmosphere into the dewer. The draw back into the dewer lasted between 0.5 and 1 second for these events. We've been maintaining 3-4 magnets here for the better part of 20 years and have never seen the like. Can any of you provide insight into this unusual observation.
Received on Thu Feb 25 2010 - 05:16:27 MST