REFLECTOR: Vent Check Valve No-Yes

[Mike Dawson]

Without the check valve in the vent line don't you get that fuel smell permeated in the interior. That is what it is for, let the air in , keep the gas out!

--- On Sun, 3/13/11, Scott Derrick <scott at tnstaafl.net> wrote:

> From: Scott Derrick <scott at tnstaafl.net>
> Subject: REFLECTOR: Vent Check Valve No-Yes
> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
> Date: Sunday, March 13, 2011, 11:42 AM
> I'm not too sure about the vent check
> valve that has been added to the kit.
> 
> The general description of the vent system is to plumb all
> vents, L&R tanks and sump into a block high on the cabin
> side of the fire wall.  A feed line is plumbed into the
> same block that travels down to the bottom of the fuselage
> and is  positioned or set up to apply positive pressure
> to the vent system in flight.  Mime is plumbed to a
> little NACA scoop on the bottom of the fuselage.
> 
> At some time after 2000,  a one way valve was added to
> the feed line to only allow air into the system. Why? 
> I'm assuming it was to prevent fuel from leaking out of the
> vent system in case of an accident or something?  Or
> was there a different reason?
> 
> I bought a valve recently and have yet to add it as I've
> flown the plane for 600 hours with nary a problem with the
> fuel system.
> 
> The problem with adding this valve is it prevents pressure
> from escaping the system.  Fuel tanks are vented to
> allow air in and to allow vapor out when the fuel expands
> from heat. We've all filled up an airplane, parked it on the
> ramp, only to discover it puked a puddle of fuel onto the
> ramp as the cool fuel heated up in the sun.
> 
> Now that valve won't let that happen, and if your system is
> tight you will be pressuring it as the fuel heats up. Is
> that a problem?  I don't know..  A couple of
> months ago I calibrated my fuel tank sensors, adding fuel
> into each tank in 5 gallon increments until full. I had
> planed on flying immediately after words but something came
> up.  I pushed the plane back into the hanger but the
> sun was shining in on the plane. I was futzing with
> something on my workbench when I heard dripping.  I
> looked arouns and saw a stream of fuel dripping from the
> bottom of the fuselage!   Just like I've seen
> from Bonanzas, Cessnas, etc..  I got all excited and
> looked into the cabin thinking I would find a cabin full of
> fuel, nothing.  I looked under the fuselage and could
> then see it was coming out of the vent  It then
> stopped.  I popped a fuel cap and left it un compressed
> so anymore pressure wouldn't build up while the tanks were
> completely full!  Now if I had that vent in there, the
> pressure would have built up, and up?
> 
> How high, I don't know.
> 
> 
> Scott
> 
> -- 
> Stand porter at the door of thought.
> Mary Baker Eddy
> 
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