Fuel / Vapor Return Lines for FI Lycomings

[rickmellor]

I got more info from AFP ... they confirmed everything you guys were educating me on. Je comprends tout!

On the swivel tee thing ... it turns out it's used to route the relief valve output on the pump back to the inlet so it can circulate. So ... I'll need to do both: 1) route the purge valve output back to the tanks somehow and 2) hook the relief valve up to the inlet so the pump doesn't over-pressurize the line to the injector body. Simple.

Thanks for the help!

[JoeBlank]

Originally Posted by rickmellor

Joe,

Are there any issues with fuel purging overboard when you tee into the vent line? I like the idea of saving a line run to the tank, and I much prefer this over purging back into the intake lines. I just don't want to spit gas out on the ground everytime I start the engine.

-Rick

Rick,
First of all, you are not purging the fuel overboard. Most if not all simply returns to the tank you have plumbed into. I haven't noticed much of a fuel drip coming from that tank vent during the purge operation. If you select the same tank when you do the purge procedure (which I do), then you have a continuous loop and little if any fuel drips. I have seen this done on several aircraft and it works fine. Also, you will only need to do this procedure on rare occasions when it is very hot out and you have just flown, shutdown and let the plane sit for a while. This may have to be done more in warmer climates than we have up in the NW.

Joe

[n8zg]

Rick,
The swivel tee can help simplify the plumbing between the fuel selector valve and the Airflow Performance fuel pump assembly. Airflow's pump kit includes a high-pressure by-pass valve to prevent fuel stoppage in the event of a clogged filter. The tee provides an alternate path around the filter, and the simplest place to put it is right on the outlet of the Andair valve. The swivel allows you to clock the 90-deg leg to suit your particular plumbing situation without over-torquing the parts.

[Noah]

This is a year old thread, but since I've been researching AFP's fuel pump installation and reading a lot of these old threads, I thought I'd correct the previous post from Neal George. There seems to be a common misconception that the AFP fuel filter contains a bypass which will allow fuel flow if the filter becomes clogged. This is incorrect. Study of the Vans drawing regarding the high pressure AFP pump shows that the PUMP is bypassed via a check valve (allowing fuel to the engine) when the electric boost pump is off. However, there is no bypass around the FILTER in the standard configuration. The pressure relief valve does not allow flow to bypass the filter as it will only flow in one direction (the reverse direction). You have to make a diagram to see this clearly. So a truly plugged filter will lead to a very bad day.

Highest Regards,
Noah Forden
RV-7A finishing
Rhode Island