Site Preparation
Cryogenic cooling requirements
20
These contaminants could clog the expansion orifice or affect the proper
operation of the GC.
Additional requirements for the liquid CO
2
system include:
• The tank must have an internal dip tube or eductor tube to deliver liquid CO
2
instead of gas (see Figure 5).
• The liquid CO
2
must be provided to the GC at a pressure of 700 to 1,000 psi
at a temperature of 25°C.
• Use 1/8-inch diameter heavy-wall stainless steel tubing for supply tubing. The
tubing should be between 5 to 50 feet long.
• Coil and fasten the ends of the tubing to prevent it from “whipping” if it
breaks.
• Do not install a pressure regulator on the CO
2
tank, as vaporization and
cooling would occur in the regulator instead of the oven.
• Do not use a padded tank (one to which another gas is added to increase the
pressure).
Figure 5. Correct and incorrect liquid CO
2
tank configuration
WARNING Do not use copper tubing or thin-wall stainless steel tubing with liquid CO
2
. Both
harden at stress points and may explode.
Dip tube
Correct configuration Incorrect configuration
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