Changing Header Tank, Fuel and Vent lines-Hints, Tricks, Experience Welcome!

[PNWJARED]

Am I missing the point of this line. the fact it is called a vent line typically means this line has air?? Is it not a vent line? or should it be called something else. to me if this line has fuel it is not venting the header tank. Though the header tank in effect becomes part of the wing tank which is vented thus not really requiring a vent at all??? So what is the point of having it??

[Av8r3400]

It vents the air out when initially filling. After the tank is filled with fuel the line then also fills with fuel.

[PapuaPilot]

That's a great question. It is a vent line. It taps into the top of the header tank and goes into the top of the fuel tank. If there is any vapor that goes back to the header tank from the fuel pump or engine it should get back to the tank via this line. The fuel supply lines come out of the lowest point of the tanks and go into the header tank. The vent line should always have the approximately the same fuel level as the fuel tanks.

If you have fuel in either tank it will go by gravity to supply the header tank.

The purpose of a header tank is twofold:
1. To provide a place for vapor to go to return to the fuel tank. The return from the engine or fuel pump needs to tap in above the fuel supply to the engine so it doesn't just draw air back to the pump/engine. The vapor return from the header tank to the fuel tank needs to be at the top so the air can rise back to the fuel tank.
2. It provides a place for reserve fuel in case of interruption of fuel flow from the wing tank(s). Using the Kitfox as an example: if your left wing is empty and you unport the supply line from the right tank by uncoordination, doing a slip or negative Gs there is still going to be about one gallon of fuel in the header tank. Even if a bubble of air gets down to the header tank it is going to stay in the top and return in the vent line.

[PNWJARED]

Thanks Guys, you were a great help!!