Varian 1079 Injector (3800 GC)
Posted: Tue Jun 09, 2009 11:57 am
by WK
Hi All,
Can anyone tell me why - when I have the split flow as OFF there is still flow out through the split line (equivalent to the flow at the split ON event?
Thanks in advance
WK
Posted: Tue Jun 09, 2009 1:02 pm
by Peter Apps
It's because during splitless operation the bulk of the gas flow bypasses the inlet, rather than being shut off as it was with the older inlet pneumatics. There is a diagram in the inlet manual.
This arrangement is a consequence of back-pressure control of the pressure in the inlet, which requires mass flow control of the flow to the inlet. When this arrangement was first commercialised the advantage that it can maintain inlet pressure even when there is a leak was punted as a major step forward, but this is true only for high flow rates, and with wide connecting lines, and if you have those an "old fashioned" front-pressure control system is also robust to leaks.
As far as I know all GCs now have back-pressure control.
Peter