36 400/54 Premium Shielded NMR Magnet System Product Overview
3 Maintenance
• Check the condition of the baffles. If they become torn or
cannot be straightened, then consider a replacement set.
• Check that the nitrogen vent is clear and is not iced- up.
• Check that the cryogen monitor was reset to the
minimum sample rate (“normal”).
• Check that the siphon entry fitting is tight. (Wait for the
ice to melt before checking.)
• Check that all seals are correctly made and are leak- tight.
(Check that the o- ring and carrier between the manifold
and nonreturn valve was correctly tightened with the
clamp, and that the bung and baffles were correctly fitted
with compression seals.) The correct compression seal
arrangement is shown in the following figure.
Figure 3 Compression seal arrangement
Cryogen and service log
It is good practice to keep a log of cryogen usage and
maintenance. An increase in cryogen consumption over time
can indicate that the vacuum space needs to be repumped. A
reduction in boil- off can indicate a leak or blockage. In
addition, it is useful to calculate the helium transfer
efficiency during a helium fill. Calculate the efficiency by
comparing the volume of helium used from the Dewar, to the
volume increase in the magnet helium can (75% to 85% is
usual for a 2m span siphon). A degradation in helium
transfer efficiency can indicate poor vacuum in the transfer
siphon, or a damaged siphon.
A suggested layout for a cryogen and service log is shown in
the following table:
To Next Page
Loading...
