REFLECTOR: Vent Check Valve No-Yes

[Scott Derrick]

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