Dennis,

We have removed the fan from inside the Conflow and have a gentle pull from
the fume hood duct that is across the room and through the wall.  The
exhaust tube connecting the Conflow to the fume hood duct is about 1" in
diameter and about 30 feet long.  The result is a fairly gentle pull.

When I take the exhaust duct tube off the top of the Conflow the mass 28
signal decreases about 0.2 v and the signal actually bounces around a bit
more (+/- 0.1 volt) than when the exhaust tube is attached to the top of
the Conflow.  The only hole in the Conflow is in the back where the MS
fused silica capillary goes through a swagelock connector that is basically
open because the diameter of the capillary is so small.  When I take my
handheld He leak detector and look for a He leak at this open swagelock
fitting when the exhaust tube is connected to the top of the Conflow, I can
not find any He coming out of the Conflow.  So not only is there no CO
coming out of the Conflow into the lab when the exhaust tube is attached,
the signal appears to be more stable.

I think that these fans inside the Conflow may build up pressure if the
exhaust tube diameter is too small or very long.  My fume hood pulls at
least 125 cfm, but the pull at the top of the Confow is very gentle and
although you can feel the suction on your hand, it will not hold the tube
to your hand like a vacuum cleaner hose.

Hope this helps and is not too confusing?

Bill



>I am wondering if Ty or Bill encountered any instability problems with the
>venting methods they have used?

Bill Showers
Dept of Marine, Earth & Atm Sciences
Box 8208
North Carolina State University
Raleigh NC 27695

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