6.4 Checking The Liquid Nitrogen Level
Every time you remove or insert a vial, note the level of liquid nitrogen (LN) in the tub. You should top off the LN when needed as a matter of routine. If your programmed grinding cycle includes more than twenty or thirty minutes of actual grinding time, you should visually check the nitrogen level at about that point and add more if needed. We do not recommend cumulative grinding time of more than thirty minutes per run, as after that much grinding the LN level is close to the point where the LN sensor will shut down the mill. However, if you must run the mill for an extended time, and the LN sensor stops the grinding program, the mill can be refilled with LN and the grinding program resumed where it stopped.
The 6870 Freezer/Mill can be refilled automatically with the 6820
6.5 6820
Description: the 6820
LN transfer hoses can vary with the LN supply tank or line, so one is not included with the 6820
LN tanks come in two types,
with maximum pressure of about 20 psi.
Installation: install the safety valve on the outlet of the tank or LN line, with the gooseneck tilted up and the valve outlet down. Then attach the LN transfer hose to the safety valve, and the other end to the inlet on the Freezer/Mill. The safety valve should be higher than the LN inlet on the Freezer/Mill. The purpose of the safety valve is to have an outlet for nitrogen vapor in case the mill and supply tank valves are both shut, and pressure builds up inside the hose.
When installing the safety valve and transfer hose, use Teflon plumber’s tape on all joints, and tighten the nuts with a wrench. If the joints leak, tighten them further and/or use more tape.
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