14 Flow and Pressure Modulesï€
Operation Manual 205
Example: Using the PCM Channels
The two channels in a PCM are different. Channel 1 is used to supply a pressure. Channel 2
may be used in the same way, but can also be used to maintain a pressure by reversing the
input and output connections.
Channel 1: Forward-pressure
This is identical to the carrier gas channel for the packed column inlet.
Channel 2: Two-way channel
If gas is supplied at the threaded connection and delivered by the tubing, this operates as a
forward pressure regulator. But the connections can be reversed—requiring some fittings—so
that it will maintain the gas supplied to it at a fixed pressure. In this mode it behaves as a
controlled leak.
This can be used to maintain the gas in a gas sampling valve at a fixed pressure, even if the
supply varies somewhat. The result is improved reproducibility in sample amount.
The figure shows the connections with the valve in the Load position.
Valve
PS
Sample in
Carrier in
To column
Back-pressure regulation
Sample out
Vent
connection
Threaded
connection
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