116 Advanced User Guide
6 Valves
Sampling valves have two positions:
Load position The loop (external for gas sampling, internal for
liquid sampling) is flushed with a stream of the sample gas. The
column is flushed with carrier gas.
Inject position The filled loop is inserted into the carrier gas
stream. The sample is flushed onto the column. The run starts
automatically.
Carrier gas may be provided by an (optional) PCM channel. To
do this, configure the column and specify the PCM channel as
the inlet. The channel then becomes programmable with four
operating modes.
The sampling valve control parameters are:
Load time Time in minutes that the valve remains in the Load
position before becoming ready.
Inject time Time in minutes that the valve remains in the Inject
position before returning to the Load position.
The sampling valve cycle is:
1 The sampling valve rotates to the Load position. Load time
begins. Valve is not ready.
2 Load time ends. The valve becomes ready.
3 If everything else is ready, the GC becomes ready. If anything
is not ready:
• If you are using Clock Table or sequence control, the GC
waits until everything is ready, then executes the valve
inject command.
• If you are not using Clock Table or sequence control, the
valve injection can be made at any time from the
keyboard.
4 The sampling valve rotates (keyboard command or sequence
control) to the Inject position. Inject time begins. The run
begins.
5 Inject time ends. Return to step 1.
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