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Re: REFLECTOR: Fuel tank venting

I think it goes something like this:  The gravity pressure head from the
surface of the fuel in the main tanks to the sump tank (say, about a foot,
or 0.4 psi) is the available pressure to the sump tank.  However; the
available (negative) pressure head available to clear a vent line is the
difference in the level between the two main tanks.  Still, in a relatively
horizontal vent line, an inch or two of difference in level should easily
clear any fuel that gets into the vent line.  So make sure there is no big
dip in the vent line between the tank and the manifold that takes it below
the upper surface of the tank.

And watch out for cap leaks.  Based on my statistically small sample (two
caps, one leaked seriously) there may be a 50/50 chance of a cap leaking.

Is any of this consistent with the information we have on the case that
brought up this issue in the first place?

Al Gietzen
-----Original Message-----
From: Bob Kuc <kucb@ix.netcom.com>
To: reflector@awpi.com <reflector@awpi.com>
Date: Wednesday, March 03, 1999 6:46 AM
Subject: Re: REFLECTOR: Fuel tank venting

>However, if one builds the vent line with a little down flair and the tanks
>are topped off to full to where it is above the vent line opening, won't
>that stop the vent line from working?  If there is any air that can come in
>the vent line, fuel should be flowing, unless the fuel cap is not seated
>What I got from the initial e-mail was the tanks were top off to full.
>they landed and opened up the cap, that allowed the tanks to "equalize" and
>thus no more problems.
>In another related question, if you drill small holes in the bottom of the
>vent line, if you are climbing, won't fuel fill the holes and thus put fuel
>in the vent lines and stop the venting?   The small holes should help on a
>descend since air can come in the small hole.  I also understand that any
>small hole should let the tanks vent, however, the bigger the hole the more
>it vents.
>When I built my top strake, I glassed a "tab" across the fuel cap
>approximately 1 1/2" below the fuel cap.  IF I put that much fuel in, I
>then know how much fuel I have in the tanks.  This line is below my fuel
>vent line to avoid "over filling" the tanks.  This also gives me the
>ability, when I do not fill my tanks, to say "fill to tabs".
>Bob Kuc
>173 FGE