Fuel tank venting

Several years ago Phil de l'Etoile, Brave Duck #67, discovered his fuel vent lines were clogged with fuel. This week it dawned on me that every LNVT with fuel vents on top of the tank will suffer the same problem. That's because after leaving the tank, the 3/4" vent hose must dip down to get under the floor joist. It's only a matter of time until the dip fills with fuel. Fuel-filled vent lines also explain why there have been so many Forum discussions concerning filler port fuel eruptions during refueling operations.

Phil's solution, which is fix-and-forget, is pictured below. The vent on the port forward tank was relocated to a new location about 2" down the tank's side. This required drilling into the tank and installing a 3/4" fitting. The abandoned fitting on the top of the tank was plugged. Then the two forward tanks were connected together with 3/4" hose. A 'T' was put in the connecting hose and leads to the cabin-sides vent port. Care was taken to make sure the vent hose slopes only upwards from the 'T' to the cabin-sides vent port. Now, any fuel that enters the vent hose will automatically be routed back to the port forward fuel tank. The aft tanks were vented in a similar fashion except the starboard tank had the new fitting installed. To work properly, the tanks with the new taps can be filled no higher than those taps. This results in a reduction of fuel carrying capacity of approximately 30 gallons ( 2" x 2 tanks x 7.5 gal/" = 30 gal).

Another solution, which admittedly isn't fix-and-forget, is to pretty much leave the venting system as-is but install a trap to give the fuel caught in the vent hose someplace to go. From the aft tank the vent hose runs forward and constantly downward until it arrives abeam and about 2" below the forward tanks vent port. Here the forward tanks' vent 'T's in. Another 'T' just forward leads the hose ever-upwards to the cabin-sides' vent port. Attached to the downward facing leg of the second 'T' is a piece of clear 3/4" hose, about 2' long, which is capped on the bitter end. Since the clear trap line is lower than the vent, it will collect any fuel. Only when the trap is full does it need to be drained.

Starboard tank shows vent on top while port tank has vent on side

Here the starboard vent has been relocated to the side of the tank while the port vent is on top.