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Column switching with diaphragm valves
Column switching
with diaphragm valves
The columns are connected via 6-way diaphragm
valves. These valves are installed in the oven. The flows
are adjusted with needle valves such that the flow
through the detector is influenced as little as possible
by the valve switching. Valve switching is only condi-
tionally suitable for capillary columns, we recommend
live switching.
How a diaphragm valve functions
valves
Column switching with diaphragm
6 - 14
Valve position Straight
The valves "Back" and "Cut" are switched such that
columns A, B and C are connected in succession.
Carrier gas flows through the injection valve Inj. to
column A, from there via valve Back to column B,
and then on via valve Cut to column C
Column A is often filled with a nonpolar substance.
The uninteresting components with a higher boiling
point are retained there, the interesting components
are passed on to column B.
Valve position Cut
As soon as a component which is not of interest or
which interferes has left column B, the cut valve is
switched over. This component is then flushed into
open air via Cut outlet
Shortly before a component of interest reaches the
outlet of column B, the cut valve is switched over
again. The component is passed on to column C
NOTE:
The cut can also be used for distribution onto another column.
Valve position Backflush
Once the last component of interest as left column
A, the backflush valve is switched over
Carrier gas flows backwards into column A via the
valve Back and also via the needle valve NV 2 into
open air through the backflush outlet Back outlet.
All components still present in column A are
flushed backwards out of the column
Carrier gas flows via needle valve NV 1 and via the
backflush valve to column B.
membran.chp, Issue August 17, 1999
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