Cryomech LNP-40, Инструкция по установке, эксплуатации и текущему обслуживанию

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Operation
7-18
7.10.8 Moisture has entered the dewar
SYMPTOM A. The level indicator reading fluctuates.
B. The level indicator not reading the actual volume of liquid.
C. The dewar is under vacuum or when extraction line opened,
vacuum is felt rather than pressure.
POSSIBLE
CAUSE 1) Not purging the dewar before the initial startup.
2) Filter element maintenance required in the filter bank.
3) Automatic drain valve not working correctly.
4) Air compressor maintenance required. ( i.e. draining moisture
from the compressor)
5) Extremely hot and humid installation environments.
REMEDY 1) *Follow procedure below*
2) If the filters have not been changed regularly, perform scheduled
maintenance and proceed to procedure below.
3) Test the automatic drain valve to ensure working properly. (7.4.1)
4) If the air compressor has not been drained regularly, drain
moisture from the air compressor and perform procedure below.
5) A refrigerated air dryer should be installed in between the air
compressor and the filter bank assembly.
PROCEDURE
The best way to fix this is to empty the Dewar completely and warm it up.
Once the Dewar is warm (room temperature). The "high" pressure line can
then be flushed with isopropyl (alcohol) *
see picture below* . To do this the
small (1/8") copper line that connects to the top shell of the Dewar can be
removed and alcohol can be flushed through the line. To confirm that the
alcohol is flowing though the line, the cold head needs to be removed
from Dewar and you will be able to see the small line with a 180º bend in it
coming up from the bottom of the Dewar. There should be alcohol dripping
from this line. Once this is confirmed-reinstall the cold head and pressurize
the Dewar (connect the nitrogen flex line from the filter bank) and you should
feel a small flow of pressure coming from the line. Allow the Dewar to remain
like this for 2 to 4 hours. Reconnect the 1/8" line and open the extraction line
slightly to begin the purging process. Once you have purged the dewar
through the extraction line for 4 to 6 hours, overnight is best. Close the
extraction line valve and start the system. This should fix the level indicator
troubles, but they may show up again.
11Jan10