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38 NIRvana
™
-LN System Manual Issue 4
4.10.1 Fill Procedure
Perform the following procedure to fill the Dewar on a NIRvana-LN detector:
1.
Loosen the retaining nut a few turns, then remove the LN Dewar port cap by pulling
it straight out. See
Figure 4-5 .
Figure 4-5: Dewar Ports and Valve
2.
It is recommended that an LN transfer Dewar with a pouring spout be used to transfer
LN from the storage tank to the detector. When using a funnel, place a thin vent tube
into the Dewar through the funnel to reduce splashing due to boiling LN.
3.
Pour approximately 100 ml of LN into the Dewar. Stop for 5-10 minutes until a
“geyser-like” vapor burst from the Dewar opening has been observed. This burst is
normal and is related to thermal equilibrium having been achieved between the LN and
the Dewar container surfaces.
4.
Fill up the Dewar (approximately 2.2 liters for the standard Dewar.) To test the LN
level, briefly insert a straight piece of wire (i.e., a cryogenic “dip stick,”) into the Dewar
and remove it. The LN level will be indicated by the condensation on the wire.
5.
Once the Dewar has been filled, replace the filler cap and hand-tighten the retaining nut
by giving it about 3/4 turn (or more) beyond the point where the nut feels snug.
WARNING!
Ice buildup may occur at the pressure relief valve ports if the detector is
being operated under high humidity conditions. Ice buildup could
prevent the valves from venting properly. Because the venting safety
bell covers the valves, this condition would not be readily apparent.
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