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Never vent the turbo pump through the vacuum isolation valve whether the pump is
turned on or turned off. Although this will not immediately destroy the vacuum pump, it
will likely stall the pump and decrease its life. Always close the vacuum isolation valve,
turn off the pumping system, and open the turbo vent valve if the valve is not configured
to open automatically.
4.4.4 Purging the
Vacuum Chamber
The purge valve shown in FIGURE 4-9 is used to purge the chamber with dry nitrogen
or dry inert gas such as argon. It is most commonly used when warming or venting the
system. During warm up, purging with dry gas can speed the warm up process
(section 4.5.4, step 6). When opening a system, purging with a dry gas will prevent
moisture and contaminants from entering the chamber, which will reduce pump-
down time and improve vacuum quality. If available, dry argon is recommended
because it is a heavy gas that is easier to evacuate with the turbo vacuum pump.
Follow this procedure to purge the vacuum chamber.
1. Close the vacuum isolation valve and properly shut down the turbo vacuum
2. Attach the gas line to the
p
in NPT purge valve fitting. A
p
in NPT to
p
in OD
tube adapter is included in the Model CRX-6.5K spares kit.
3. Regulate the gas pressure from 6.89 kPa to 13.79 kPa (1 psi to 2 psi).
4. Open the purge valve slowly until it is fully open. In about 1 min the pressure
relief valve on the chamber will open and release gas.
5. Open the vacuum chamber lid for sample exchange with the gas flowing.
The dry gas will prevent moist air from entering the chamber; this will speed vacuum
pump down time.
6. Close the purge valve fully when the vacuum chamber lid is replaced.
If the system is accidentally left open for a long period of time, it should be cycle-
purged to reduce contamination. Refer to section 5.2.1.1 for this procedure.
The vacuum chamber is not designed for positive pressure and should never be
pressurized above 2.1 kPa (0.5 psi). The pressure relief valve on the chamber is set for
2.1 kPa (0.5 psi) and should never be disabled or modified. Failure to comply may result in
injury or death.
The vacuum chamber should only be purged with dry nitrogen, dry argon, or inert gas.
Failure to comply may result in injury or death or damage to the probe station.
Never purge the chamber with dry nitrogen, dry argon, or inert gas unless all stages and
the probe arm sensor are above 290 K.
Never vent the chamber to atmosphere unless all stages and the probe arm sensor are
above 290 K
.
