Varian 450-GC, User Manual

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Maintenance
Varian, Inc. User Manual 450-GC Page: 429
The use of soap-based leak detection fluids is NOT recommended for a high
performance capillary Gas Chromatograph due to the danger of introducing
contaminants into the system. If leak detection fluids are being used they
should only be used outside the Gas Chromatograph, i.e. to verify there are no
leaks in the plumbing to the Gas Chromatograph. If a leak detection fluid is
being used inside the Gas Chromatograph, an alcohol such as isopropanol or a
50:50 mixture of isopropanol and water should be used. Use a dropper or
syringe to place a few drops of leak detection fluid on the desired fitting and
monitor the area for bubble formation.
The most important step in leak checking is to verify that the GC system can
hold pressure. This is done by removing the column from the Injector, sealing
all exits from the Injector and pressurizing the system. Use the following
procedure to leak check 450-GC Injectors:
When conduct ing leak check procedures it is impor tant to completely
seal all carrier gas exits, includ ing septum pur ge and spli t vent outl ets. If
more than one Injector i s present, then the outlets of all t he Injectors
must be sealed. The following procedure refers t o one Injector but
should be duplicated for every Injector on the 450-GC.
1. Set the column oven and the Injector zone temperatures to 50°C and allow
them to reach this temperature. This allows safe handling of Injector
surfaces.
2. Remove Injector septum nut and install a new septum. An older septum can
often be the source of a substantial leak.
3. Remove the column from the Injector. Use the appropriate nut and ferrules
to seal the base of the Injector. For packed column systems use a 1/4"
Swagelok blank off plug (SWB400P). For capillary systems use a capillary
nut (03-949551-00) with a no hole ferrule (28-694590-01).
4. If the Injector is either an 1177, 1093 or a 1079 PTV, then the septum purge
and split vent outlets must be sealed. The septum purge outlets are located
on the top frame surrounding the column oven, behind the column oven
door. The split vent outlets are located on the left side panel of the 450-GC.
Seal the septum purge by removing the outlet fitting fr om the septum purge
valve and replacing it with a blank off plug (P/N SWB200P). Seal the split
vent outlet by installing a Swagelok union on the outlet tube and sealing it
with a blank off plug.
5. With all outlet ports plugged, pressurize the system to 20 - 30 psi. This can
be accomplished by adjustment of manual pneumatic controls or Electronic
Flow Control (make certain that the split ratio is turned to off, constant flow
is not selected and the septum purge valve, if appropriate, is turned off).
For information on setting carrier gas pressure see the Basic Operation
section of this manual.