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8
Liquid Nitrogen Autofill System
The optional autofill system automatically refills the 75 litre unpressurised dewar from a
pressurised supply dewar.
Warning:
There is always a possibility that this autofill system will fail, resulting in the
entire contents of your pressurised dewar being spilt on the floor. You MUST
have a contingency plan so that you can deal with this safely. An autofill system
is not likely to be safe in a small or medium sized room, unless you use safety
devices such as oxygen level alarms and self-contained breathing equipment. The
autofill system is recommended for use with portable pressurised dewars (of 160
litres or less), not with large nitrogen tanks.
Warning:
A pressure relief valve has been fitted to the supply pipework on the autofill to
safely discharge any pressure generated by liquid nitrogen trapping. This valve
should NOT be removed without consulting an expert.
The autofill system consists of the following components.
•
Nitrogen level probe
•
Level probe cable
•
Nitrogen hose with solenoid valve
•
Nitrogen level meter with IEC power cable.
The pressurised supply dewar is normally provided by the customer.
The level meter has its own detailed manual, but this section describes the basic operation
as part of an autofill system. The level meter has already been set up to function correctly
in the 75 litre Cryojet dewar. The display shows the depth of liquid, expressed as a
percentage of the maximum depth, which is 805 mm for the standard 75 litre Cryojet
dewar. Do not run the Cryojet below 13% depth (10 cm), as this will impair the
performance.
The level meter is set up in the factory with the following default settings.
FULL
95%
Filling stops at this level
FILL
15%
Filling starts at this level
LOW
10%
Warning light appears on level meter.
Each level meter is set up for the level probe supplied with it. If you use a different probe,
or you use the probe in a different dewar, re-calibrate the level meter as described in its
manual.
