Fuel System Flushing

[Ironflight]

Although I have been tinkering with airplanes most of my life, one thing I have never had to do was flush a new fuel system before starting the engine for the first time. I've looked through my bookshelves and can't find any good procedural discussions...before I take out a second mortgage to buy a full load of fuel, can anyone give me a quick description of the process?

I would assume it is to put a limited amount of fuel in each tank, turn on the electric pump, and flow fuel up through the gascolator, with the fuel line disconnected at the carb.... but how do I know when I've done enough - and am I completely off track?

Paul Dye
RV-8 finishing....

[robertahegy]

That's basically what I did. Run the pump and check the fuel flow while you purge trash out of the tanks and lines. Run a measured amount and time it to ensure that the GPH is sufficient so you are sure you have no restricted flow. I calculated about 45 gph from my little facet pump.

I had QB wings and tanks and still find little shards of AL sticking in the sump drains. Ocassionally I unscrew the drains and let some fuel dump as I replace the drains with ones that have new O-rings.

Roberta

[osxuser]

I'd fill them all the way up, let the fuel set a while, then pump out a few gallons from each. From then on, keep them full. The reason you should fill it up all the way is because you want to wash any **** into the bottom.

[f1rocket]

You can kill three birds with one stone, so to speak. Fill one tank full. Disconnect the fuel line into the carb, or FI Controller if so equiped. Turn on your electric fuel pump and fill a 5 gallon gas can and time it. Now, you can calculate your fuel flow. Second, you can begin to calibrate your fuel level indicators. This is especially helpful if you have any electronic displays that require careful calibration. Third, you're thoroughly flushing your system.

Filter the fuel as you pour it into your other tank. Repeat the procedure on the other tank once you've filled it.

Once completed, disassemble all filters and strainers to clean out any debris. Again, this is very important if you have a fuel injection system as the smallest particle can clog an injector and make for an interesting first flight.

[Mel]

If using this method to calculate fuel flow, be sure the airplane is in the MAXIMUM climb attitude.
Mel...DAR

[f1rocket]

Originally Posted by Mel

If using this method to calculate fuel flow, be sure the airplane is in the MAXIMUM climb attitude.
Mel...DAR

Yes, good catch Mel.

[osxuser]

Also, if using bendix FI don't forget the last chance screen behind the fuel inlet hose in the metering unit.

[Ironflight]

Thanks for the ideas - espcially doing one tank at a time and getting the flush, tank cal, and flow rate - good thinking Randy!

One question...is the fuel flow rate measurmenet a requirement for cert Mel? I know that you are supposed to do it for a new design homebuilt - couldn't remember that it has to be doen for a kit - but since you'll be my DAR, I guess it's your opinion that counts!

Paul

[Mel]

It's not a hard set mandatory rule; BUT it is STRONGLY recommended.
Mel...DAR

[f1rocket]

Originally Posted by Ironflight

Thanks for the ideas - espcially doing one tank at a time and getting the flush, tank cal, and flow rate - good thinking Randy!

One question...is the fuel flow rate measurmenet a requirement for cert Mel? I know that you are supposed to do it for a new design homebuilt - couldn't remember that it has to be doen for a kit - but since you'll be my DAR, I guess it's your opinion that counts!

Paul

Since you are essentially designing (or at least fabricating) a one-off fuel system, you should check to make sure that it can deliver over and above the necessary GPH needed to sustain flight. Who knows, you might have a severe blockage somewhere or at least a leak.