ORIGINAL: delateurj


To clarify, I am not suggesting using the pressure line to force anything out.

The 3 line approach has two lines in the bladder. One is the feed line set up same as 2 line approach, simply fuel tubing in middle of bladder. The pressure line goes to the provided pressure line tap in the outside casing of the tank, same as two line approach. The 3rd line is a vent that goes to the top to one of the little humps in the top of the tank inside the bladder. As you fill, air rises to the top and vents out. Eventually all air is theoretically displaced by the fuel and comes out the vent line until it is full of fuel. The the fuel causes the bladder to expand theoretically. I agree there is a practical chance that some air may not come out or the bladder may not expand completely and you'll get a less than full tank. One way to see the practical performance vs. theoretical is to actually try it outside of the plane. I have multiple times as that is how my engine test stand is set up and it seems to work. I also use this in my stock T-34 racers initially for the rule reasons I mentioned (no syringe fueling allowed) and since it worked well for that, I use it even when not required by the rules.

- Joe.