Gow-Mac 5900 Series, Operating Manual

Page: 31 / 38

Series 5900 DID GC
1019, Rev. 1
31
D. Backflush Valve: The 10 port backflush valve is used to allow impurities to pass through
the column ahead of the “heavy” sample gas with longer retention time. The sample loop
will inject the sample gas onto the “precolumn” which will separate the smaller/lighter
impurities and allow them to pass to a primary column or directly to DID. As soon as the
impurities of interest are through this precolumn, the valve will rotate to the CCW position
where the heavy retained gas will reverse carrier flow and purge out to vent preventing it
from reaching the DID. This will prevent saturation of the DID and minimize recovery time.
A general rule of thumb is to backflush the heavy gas at a 3:1 ratio, meaning there should
be 3 minutes of backflush time for every minute into the precolumn.
E. Foreflush (or Heartcut) Valve: The 4 port foreflush valve is opposite of a backflush
valve and is used to purge a lighter gas that elutes before the impurities of interest.
The sample loop will inject the sample gas onto the “precolumn” which will separate
the smaller/lighter sample gas and purge it to vent. As soon as the bulk gas elutes and
vents, the impurities of interest will continue to pass through the precolumn and the flow
path is returned by moving the valve back inline to a primary column.
F. Detector/Vent Valve:
The 4 port Detector/Vent valve allows residual sample or large
impurities that were not foreflushed to be purged to vent before it reaches the DID. This
is considered a last line of defense to prevent DID saturation or baseline disruption.