Fuel Filters, Wing Tanks

[djmc4344]

I'm right in the middle of changing out all my fuel lines, getting rid of the orginal factory stuff. Is it over kill or a good idea to have fuel filters from the wing tanks to just before the header tank and one filter just before the carb inlet. Opinions and thoughts on this appreciated.

Thanks

[Av8r3400]

My opinion and its only one man's opinion:

I do not like the idea of a filter between the wing and header tanks. The only flow there is via gravity. A small amount of water contamination could block the flow through these filters. Personally, I only like a filter where a pump provides positive flow through it.

[Dave S]

Hi Dan,

I unequivocally second Larry's comments. There should be no filters, for that matter - no partial restrictions of any kind, in the line between the main tanks and the header tank.

I had to experiment with this to settle the issue for myself. During my fuel system testing BEFORE first flight I experimented with a filter on each side. I found that all you had to do to get the fuel flow to stop is get a slug of air into one of the filters - the combination of fuel wetted filter and air sealed against the rather small amount of head pressure (remember the header tank vents back to the right wing tank balancing off most of the potential head pressure). This caused the flow to stop - it could be restarted only by significantly pressurizing the wing tank to overcome the cavitated wet filter. THE FILTERS WERE REMOVED FROM BETWEEN THE HEADER TANK AND WING TANKS before the first flight and the whole assembly replaced with a single one piece hose on each side.

You might think I am overstating the situation a bit - if you saw it happen in front of your face - I don't think you would consider deviating from the design specification.

That's just my opinion - based on experimentation with the setup.

Sincerely,

Dave S
KF7 Trigear

[Dorsal]

I support the last two posts, keep in mind that the tanks only balance with the differential pressure between them, that may only be a few inches of head for significant asymmetric draw. It does not take much (as pointed out above) to cause this to occur.

[Mnflyer]

Count me in with the 3 previous posters I agree 100% no filters on the tank lines.

[djmc4344]

Thanks for the advice guys, I think I'll go with one good filter.


I currently have a clear filter on each down line and one just before the carb. I have been experiencing unequal flow especially from the left tank it seems to draw down much faster than the right take. I think it may have something to do with filters I'm using.

I'm changing the tank hose to header to 3/8 I.D, I have 5/16 aluminum tube to the firewall. Then I will install either 5/16 or 1/4 I.D line from the firewall to the carb. The carb inlet is 1/4" I think.

[DesertFox4]

Sorry guys, my model 4's been operating just fine for 750 hours with filters and valves in the fuel lines between wing tanks and header tank. My previous model 3 , same thing for 1400 plus hours. Several Kitfox in "the Valley" are set up the same way with thousands of trouble free hours.
I do use blue Tygon type fuel lines so I can always see my fuel flow on both tanks and see-through filters. So far so no feeding issues in any attitude possible including limited aerobatics.

[sdemeyer]

I also run filters between each tank and header tank. Never had a problem in 225+ hours. I change the filters twice per year.

[DesertFox6]

Very sound reasoning all along here, but what else would one expect in this forum? My experience matches Steve's; 11+ trouble-free years on my Model IV Speedster (including positive-G aerobatics) with separate valves and filters on both wing-roots. I built my bird with a lot of "maintainability" features following 30 years' experience with military aircraft, not all of which were "maintainer friendly," lemme tellya.

Initial use of see-through Volkswagen (gasp!) one-way fuel filters was for early detection of possible contaminants following construction; early fill-ups really cleaned out my tanks, so a couple early replacements were expected and "clearly" necessary. The filters plug into the Tygon tubing perfectly and since there's never been a problem, I've kept using them. Annual swap-outs take about four minutes per side, including fiddle-time with the securing clamps...and you can tell if/when something funny is going through the lines before it disappears into the header tank and engine feed line...I like to see what I'm getting for my gas-money!

Use of in-line shutoff valves allows cutting off fuel flow from, or the total de-fueling of one wing, if working on the other, without a total defueling of both wings, when the need for emptying one side only arises. I also use this feature while refueling so I know how much imbalance I may be incurring, but no problems have yet surfaced. Using the shutoff valves while refueling also precludes fuel back-flow through the header tank up into the other wing while refueling, giving me yet another indication of how evenly each side is actually feeding. So far, I haven't found an imbalance worth mentioning.

It is absolutely mandatory to insure a constant "downhill" one-"G" fuel flow with no exceptions, in-line goodies or no. If you can insure a constant downhill slope without any changes in line slope, that's even mo-bedda! A bunch of us here in the desert southwest have not experienced the original problem in this thread, but since it was an excellent question concerning safety of flight, any amount of shared "cross-tell" has got to be helpful.

Do what your conscience (gut) tells you is right for YOU and please keep us posted: Take care and a Happy New Year!

"E.T."

[djmc4344]

Guys,

Thanks for all the responses on this subject. It's been a very informative discussion and I really appreciate your experience and expertise.
I think I will go with 3/8 ID hose from the wing tanks to the header. No filters, a large ID hose for the fuel to flow with no restrictions from the wing tanks to the header is what I want. I may put some clear plastic tubing so I can see the fuel. Also going to add shut off valves between the wing tanks and header.I already have 5/16 ID aluminum tubing from the header tank to the firewall. After that I'll use 1/4 ID hose with a good filter between the fuel pump and carb.

Regards,