REFLECTOR: Fuel venting issue

Mon Jul 2 01:41:13 CDT 2007

The current standard fuel vent system has the two
strake vent lines and the sump tank vent line all
connected up on the firewall via an AN cross. The
remaining run on the cross is pointed up - you plumb a
vent line off this last run up to the top of the
firewall and then down and out the bottom of the
plane. You want this line to exit the plane in the
center of the fuselage (assuming the exhaust stacks
exit the cowl on the sides). When the tanks are full,
and if you climb at a steep enough angle, some fuel
can escape out the vent system and you don't want it
running over the exhaust stacks! 

A check valve is "teed" into this last vent line in
case it gets plugged. These check valves can
definitely seep. I don't see any major failure modes
by placing it in the cabin, but I can't stand even a
whiff of gas in the cabin. So, I ran the main vent
line down the engine side of the firewall and teed off
of it with a check valve in the engine compartment as
well.

Here's a link to a pic on tvbf:

http://www.tvbf.org/gallery/?display=Interior%2FDscf0057.jpg

Btw, with this system the vent lines inside the
strakes don't need to be run to the highest points in
the strakes anymore. I called the factory just before
closing out my strakes - they just stub the vent lines
into the top of the aft fuel bulkhead - only sticking
into the strake about an inch. That means they are
under the fuel level when the tanks are full (yes,
they still vent when submersed via air bubbles).
Unfortunately, I learned about this after I had spent
plenty of time figuring out just where the highest
points in my strakes were and plumbing the vent lines
accordingly. Since I hadn't closed out my strakes, I
cut the strake venting down to a stub. Works great.   

Pat

--- Ron Brown <romott at roadrunner.com> wrote:

> The check valve is to prevent fuel tank collapse or
> fuel starvation from a frozen or stopped up vent
> caused by mud daubers.
>   ----- Original Message ----- 
>   From: Scott Derrick 
>   To: Velocity Aircraft Owners and Builders list 
>   Sent: Sunday, July 01, 2007 9:35 PM
>   Subject: Re: REFLECTOR: Fuel venting issue
> 
> 
>   these valves are made for liquid.  one way valves
> can seep a bit, and you would never know, except in
> this case... its only held closed by a very small
> spring.
> 
>   I'm trying to think of another plane that has a
> fuel vent open to the cabin and can't.  The failure
> mode of  this valve is potentially  catastrophic! 
> 
>   Anybody know of any certified or experimental
> plane that has this configuration? 
> 
>   Was this added because somebody crashed? 
> 
>   Can Scott Baker explain the reasoning behind this
> change to the plans and why Velocity thinks this is
> a safe thing to do?
> 
>   Scott
> 
>   Brett Ferrell wrote: 
>     Then it's a good thing it's not open to the
> cabin.  The check valve only allows air from the
> cabin into the tanks....
> 
>     B
> 
>     Scott Derrick wrote: 
>       I have a hard time feeling good about having a
> fuel vent line open to the interior of the cabin...
> 
>       Scott
> 
>       Alex Balic wrote: 
> The check valve is located inside the plane and
> above the level of the fuel
> in the tanks (right up at the roof- it T's into the
> vent system, so fi the
> external vent fails, it will open and allow air into
> the tanks from the
> cabin- but not let fuel/fumes out into the cabin.
> 
> -----Original Message-----
> From: reflector-bounces at tvbf.org
> [mailto:reflector-bounces at tvbf.org] On
> Behalf Of David Staten
> Sent: Sunday, July 01, 2007 12:49 PM
> To: Velocity Aircraft Owners and Builders list
> Subject: Re: REFLECTOR: Fuel venting issue
> 
> If the check valve is on the same line that is
> theoretically blocked by 
> ice or mud, how is it able to prevent ANYTHING? An
> obstructed vent is an 
> obstructed vent.
> 
> Dave
> 
> Brett Ferrell wrote:
> 
>   The check valve is actually there to prevent tank
> collapse should the 
> vent line become blocked (by say a mud-dauber or ice
> accumulation).  
> I've seen a 15,000 gallon steel tank collapse by a
> plugged vent, and 
> it's not pretty...
> 
> B
> 
> Scott Derrick wrot
> 
>
----------------------------------------------------------------------------
> _______________________________________________
> To change your email address, visit
> http://www.tvbf.org/mailman/listinfo/reflector
> 
> Visit the gallery!  www.tvbf.org/gallery
> user:pw = tvbf:jamaicangoose
> Check new archives: www.tvbf.org/pipermail
> Check old archives:
> http://www.tvbf.org/archives/velocity/maillist.html
> 
> -- 
> 
> -
>     Liberty means responsibility. That is why most
> men dread it.
> 
>     George Bernard Shaw, Liberty 
> 
> 
>
------------------------------------------------------------------------------
> 
> 
>   _______________________________________________
>   To change your email address, visit
> http://www.tvbf.org/mailman/listinfo/reflector
> 
>   Visit the gallery!  www.tvbf.org/gallery
>   user:pw = tvbf:jamaicangoose
>   Check new archives: www.tvbf.org/pipermail
>   Check old archives:
http://www.tvbf.org/archives/velocity/maillist.html>
_______________________________________________
> To change your email address, visit
> http://www.tvbf.org/mailman/listinfo/reflector
> 
> Visit the gallery!  www.tvbf.org/gallery
> user:pw = tvbf:jamaicangoose
> Check new archives: www.tvbf.org/pipermail
> Check old archives:
http://www.tvbf.org/archives/velocity/maillist.html

____________________________________________________________________________________
Be a better Heartthrob. Get better relationship answers from someone who knows. Yahoo! Answers - Check it out. 
http://answers.yahoo.com/dir/?link=list&sid=396545433