Fuel Tank Vents

This tasks has been on my mind for literally years.  Modifying a fuel system scares the crap out of me... 

I have a header tank... purpose of the header is to simplify the fuel system.  Fuel injection return can simply go back to the header and does not have to go all the way to the main tanks.  Can also use a simplex fuel valve, and not a duplex.  Also adds some weight up front, and 2 more gallons of fuel.

So the vents... per the manual, run the vents out the bottom of the wingtip using either aluminum tube or the plastic line.  It is well known that this vent system will leak when (1) the tanks are full, (2) parked on a slope, or (3) daytime heating when the tanks are full.

The TWTT instructions modify the vents from the original manual.  The vents are T'ed together, and you run the vent line up as high as possible under the tip.  This is better.

On the forum, many have modified the vents using a 'bleed' type check valve prior to exit.  Lets lots of air in, only lets a little bit of air out.

Lastly, the underwing / tip exit has caught many on the noggin.  The aluminum tube vent is the worst.  Some builders are now using under wing machined aluminum vents designed for RV's.  These are nice as they have a screen, 2 vent holes (1 facing forward, and a backup at the rear).

Link to JD Airparts Site Here.

So my plan is to incorporate ALL of these.  T the vents, check valve, and under wing machined vents.

My worry... the vent for the main tanks and header tank work OPPOSITE from a venting persepective.

For the main and aux tanks, the vents let air in so fuel can depart.  For the header, the vent lets air out so the header can fill.  I'm worried they will fight each other... but we will see very soon I hope.

The bleed type check valve is key.  It definitely lets some air in.

On the flip side... the pumps will create some suction and draw fuel through (I hope).

I mocked one vent assembly up last night.  Everything fits under the wingtip.

I used a 1/8" NPT male / male into the tank.  A 1/8" NPT 'T", then a 1/8" NPT to AN4 female for the check valve, and a 1/8" NPT hose barb on the other end. Going to feed the nylon line into 14" hose and clamp it to transition from the vent line to the "T".

First one (left wing) complete.

Was somewhat worried about edge clearances on the -4 fitting that holds the vent to the bottom skin.  May reinforce it... will see.

(The wings are folded currently...)

I reversed the direction of the check valve... what is shown in the picture is backwards!  That would have been disastrous...