Flush new fuel tanks?

[Dorsal]

Steve,
Good point, the vent line is a perfect 1.5psi header tank pressure gage that is not affected by relative Gs. What do you use for a fuel sensor at the top of the vent line?

[Slyfox]

I actually have the little tank with a float sensor. Mounts right on top of the header tank with hose connections to the vent just off the header and than the vent hose connects to the other side. The vent hose goes to the right tank. When the fuel empties in the line so does the little tank, thus the float sensor drops and makes contact. I than went to carquest and got a red light and mounted it to the panel.

[Dave S]

Hi Nathaniel,

I'd like to get back to your original post regarding opinions about flushing new fuel tanks.

There are probably as many opinions about this, particularly as to how to do it, as there are builders - so please take my comments and opinions as only this builder's opinions/comments.

I believe there is enough data in the NTSB records to substantiate that experimental and certified aircraft suffer fuel contamination incidents resulting in engine stoppage in sufficient numbers that this subject should be considered seriously. Some of the incidents/accidents do not work out very well for either the plane or pilot. The incidents/accidents can be filed under two categories - either the contaminant(s) was/were not cleaned out of the fuel tank before the system was put into service; or, the contaminant(s) was/were introduced into a perfectly clean tank/system.

I think the answer about what to do is going to be more than evident if each of us thinks about the absolute most inconvenient time on the first flight to have an engine puke - but that is just me.

In my opinion, the builder needs to flush the tanks before assembling of the tank(s) into the wings; and, verify that the flush has been completely effective - verify - don't guess. It is way more difficult to flush after assembly.

My choice was to plug the tank fitting holes - introduce 5 gallons of water and detergent - close the fuel cap hole - then vigorously - even violently agitate the tank (a lot) in all positions including upside to dislodge as much junk as possible. Subsequent multiple clear water rinses to get rid of the soap and crud. If there is still crud - repeat till there is none.

How do you verify that the job is done? Use a coffee or paint filter to filter the water as you drain it from the fuel tank - I did the wash/rinse/repeat thing till three consecutive filter papers showed up with no crud.

Once the detergent is all rinsed out and it has been verified that no more crud remains (meaning three consecutive filter papers showing up with no crud) then the tank should be rinsed with isopropyl alcohol to remove the remaining water (since water is a contaminant also) - again - filtering the stuff when it is poured out because solvent may dislodge crud hat the detergent did not dissolve - good enough reason to do detergent AND solvent rinse. If any additional crud shows up - go back to the detergent and follow with rinses/solvent till there is no crud left.

Once the tank is spotless on the inside - allow it to air dry under controlled conditions so the isopropyl goes away and it is certain that no bugs or other debris are re-introduced into the tank. Then seal it up and store it away till it is ready for installation in the wing.

The upshot? I did the same with the header tank - the fuel lines and did a reverse fuel wash only of the filter to be installed in the fuel line...AND... when it came time to replace the filter - cut it apart to look for crud and found the filter was absolutely clean. There have been no fiberglass strands in the daily fuel samples/filter/header tank or anywhere else - ever.

Each one of us probably has a different opinion about this - I go back to comparing the effort to clean the tanks to "what if" on first or subsequent flights.

Sincerely,

Dave S
KF 7 Trigear
912ULS warp drive

[Nathaniel]

Good post Dave. Since I know now that I have the "new" tanks from Kitfox, it is still a concern, but not as much. I plan on doing a pre-install flush, like you say. And replace all filters before the first flight, and during flight testing. By then, everything should be worked out of the system.

[jdmcbean]

Nathaniel,

Think I responded directly to you.. but for reference here is a page from the manual.

[Mark]

After flushing the tank, be sure to wipe the fuel inlet dry, dry, dry! It is very susceptible to rust almost immediately with any bit of moisture.

[Nathaniel]

Straight from the source. That settles that!

[Nathaniel]

After flushing the tank, be sure to wipe the fuel inlet dry, dry, dry! It is very susceptible to rust almost immediately with any bit of moisture.

Perhaps dry it and wipe it with a little WD40? Displaces moisture, that should help.