REFLECTOR: Fuel venting issue

[Scott Derrick]

Hmmm... 

My plane is vented per the 1996 plans,  both tanks and the sump attach 
to a block(tying then all together) on the firewall above all the 
tanks,  a single line exits the top of the block , the line goes up to 
near the top of the fuselage then down to the bottom of the plane, 
attaching to a small NACA duct to apply a very low pressurization to the 
system in flight. 

Just recently  I noticed a one way valve had been added to the single 
line running out of the block to prevent flow out of the vent line and 
thus only allow air to flow in.   I don't have this one way valve and 
wondered why I would need it?  I guess this scenario answers my question.

I had observed fuel venting out the vent line if I topped off and then 
let the plane sit in the sun all day heating up(expanding) the fuel but 
I had never seen a siphon get started.

Scott

Alex Balic wrote:
> Non vented sump tank- does the fuel vent system just goes from each tank to
> the outside independently then? If so, then probably your vent line(s) do
> not curve up to the very top of the tank first, but even if they did, if the
> exit leg is far enough down, then you would be able to start a siphon with
> them which would be difficult to stop until the fuel level dropped somewhat
> below the top most point of the vent system - can you give some more
> specific info on your setup?
>
>
> -----Original Message-----
> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
> Behalf Of Tom
> Sent: Sunday, July 01, 2007 8:34 AM
> To: reflector at tvbf.org
> Subject: REFLECTOR: Fuel venting issue
>
> Took first long flight with plane (FG/STD) this past week. When 
> refueling left tank in Huntsville fuel started pouring out of the vent 
> hole at a fast clip. It only started when about an inch from the top but 
> it worked like a siphon and lost 15 gallons. Filled it up to about 2 
> inches from top and no issue at all, tried topping off and it started 
> doing it again. I filled it in Fort Myers before departing and there was 
> no issue. Any ideas as to the cause?? Not sure if this is pertinent but 
> the sump tank does NOT have a vent line. thx Tom
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