Replacing O ring seals on magnet cryostats
BANGERTER%KEKULE@BIOMED.MED.YALE.EDU
Tue, 07 Jan 1997 11:17:46 -0500 (EST)
Chuan Wang of Rutgers raised the question of the desirability of changing
seals and getters on older cryostats. About a year ogo we needed to move a
11.7T magnet that had been cold and energized in one place for 12 years to
another room. Since the seals were 14 years old, I thought it would be
very advisable to warm the magnet up for the move, then replace the O ring
seals before reenergizing. We had oxford do this in connection with the
installation of a new system. When the old seals were examined, I was amazed
by how good their condition was. There was no evidence on microcracks, and
they were quite resilient (I know what my windshield wipers look like after
a year). So we may have been able to get away with moving the magnet cold
and under vacuum (though not energized) without problems. Since the consequence
of losing the vacuum on a cold magnet would be most unpleasant, I guess it
comes down to how lucky one feels. I would advise following the vendor's
recommendations on this point, particularly if they accept responsibility
for what may happen as a consequence of the move. Our He boiloff was the
same after as before the move (I do not remember if we replaced the getter).
We fill He on a 5 week schedule, so it is not a critical point. Personally,
I would choose to err on the side of caution and do not relish facing the
faculty if corner-cutting let to a serious mishap!
Ben Bangerter
Yale Univ.