Varian 450-GC, Руководство пользователя

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Maintenance
Page: 430 User Manual 450-GC Varian, Inc.
6. Shut off the carrier supply at the source and monitor the displayed pressure
at the GC for 15 minutes. The pressure should not drop more than 0.5 psi
in 15 minutes.
Leak checking ensures that there are no leaks in the GC system up to and
including the Injector assembly. If the indicated pressure on the GC drops by
more than 0.5 psi (3 kPa) during the 15 minute test period, this indicates that
there is a positive leak in the system. Finding such a leak, particularly if it is a
small leak, can be very difficult. In general the best approach is to
systematically go through the pneumatic system from the source and tighten
each fitting until the leak is eliminated. It is important to note t hat leaks are often
found in the carrier gas supply to the GC.
Locate leaks preferably with an electronic leak detector or leak detection fluid.
An electronic helium leak detector is available from Varian (CP87610 110 VAC,
CP80610 220 VAC, CP83610 240VAC). This device can detect helium
concentration in the air as low as 2 ppm and is very effective at identifying the
precise location of a helium leak from a GC system.
Gas Purifier Replacement
The most common gas purifiers used in gas chromatography are moisture traps
for removing water vapor, hydrocarbon traps for removing low levels of
hydrocarbon contaminants and oxygen traps for removing low levels of oxygen.
In general the choice of filter depends on the application and detector used.
Carrier gas should contain less than 1 ppm oxygen, moisture and trace
hydrocarbon contaminants. A moisture and a hydrocarbon filter are
recommended for general applications to maintain detector background levels
at their lowest possible level. If the detector used is an ECD or MS an oxygen
filter should be employed as well.
Carrier gas filters are typically located on the side or at the rear of the 450-GC.
Varian supplies several types of carrier gas purifiers. These include a
hydrocarbon trap, moisture trap and oxygen trap. While the choice of purifier
depends on the individual configuration and performance expectations, the
following configuration is recommended for maximum carrier gas purity and
protection.