For four months subsequent to energizing a refurbished 500 MHz magnet
the helium boiloff was normal (0.6%/day). Due to various delays (not
Varian's fault) the magnet is only now being shimmed to specs. When the
installation engineer recently installed the ice inhibiting heat sinks,
flow meters, and a relief valve to the nitrogen exhaust the helium
boiloff eventually pegged the flow meter and the helium dewar lost
10%/day. Boiloff returns to normal when only the nitrogen relief valve
is removed. The high boiloff returned when a new relieve valve was used
or when engineer tried every permutation of switching the nitrogen
detector and heat sinks on the three nitrogen exhaust ports. (The port
with the nitrogen level detector was cooler than the other ports but no
obvious leak was detected). I also confirmed that the relief valve did
indeed release at 0.5 psi. Varian and Oxford don't seem to be able to
explain the problem. Varian has offered to take back the magnet (at
their cost of about $20k) and refurbish it which would delay the
installation for 2 more months and the faculty has manuscripts and
grants on the line. First, does anyone have an explanation for the high
boiloff rate? Second, how risky is it to accept the magnet as is and use
it without the nitrogen boiloff relief valve. Third, if we do accept
the magnet as is what guarantees should we request that the magnet be
refurbished free of charge should it spontaneously quench or launch into
a high boiloff rate. I was thinking of an additional 3-4 year guarantee
on the magnet and returning the system back to specs.
Ted Burkey
Dept. of Chemistry
Campus Box 526060
The University of Memphis
Memphis, TN 38152-6060
tburkey_at_memphis.edu
fax 901-678-3447
voice 901 678-2634
http://www.chem.memphis.edu/burkey/default.htm
Received on Wed Nov 30 2005 - 08:52:10 MST