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Thread: Fuel Filter Advice

  1. #1
    SWeidemann's Avatar
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    Default Fuel Filter Advice

    Kitfox Folks,

    I'm looking for testimonials and field experience about fuel filters. What type & brand of fuel filter do people use and why? My latest favorite is the bronze filter element that can be installed in the engine compartment if desired (or anywhere else) and can be removed for inspection and cleaning, such as Earl's aluminum body with bronze insert. I have a technical bias against paper elements however they are being widely used. What do others use?

    Thanks much,

    Skot
    Kitfox Vixen 912 ULS
    N24V at C29

  2. #2
    Senior Member t j's Avatar
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    Default Re: Fuel Filter Advice

    I have a finger strainer in each fuel tank and a 120 micron screen in my Aircraft spruce gascolator. That's all.

    The Rotax 2 stroke installation manual says don't use paper filters. Use a fuel filter of 0.15mm (150 microns).
    Tom Jones
    Classic 4 builder

  3. #3
    Senior Member HighWing's Avatar
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    Default Re: Fuel Filter Advice

    I have glass fuel filters mounted in the down lines from each wing tank to the header tank. My lines run down along the top of the quarter window. The filters are visible as I fly and in low fuel situations as in long down runs from the Sierra crossing to home, I can visibly monitor fuel flow. I also have the finger strainers in the tanks. 900 hours on the first Model IV with this set-up and not a hiccup.

    I do have one of the filters you describe, but it came with my second hand kit and it is still in the box as I like to see what is going on without taking things apart.
    Lowell Fitt
    Goodyear, AZ


    My You Tube Channel

  4. #4
    Senior Member
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    Default Re: Fuel Filter Advice

    My preference is a combination of both Lowells and Toms.

    I like the visibility aspect of Lowells and it provides the ability to supply fuel if one filter becomes clogged.

    I believe a gascolator is necessary, but I do remove the mesh inlet filter as no need to filter twice.

    A few other points to ponder:

    Rotax recommends a 100 micron (.1mm) for 4 strokes. Most would find anything between 70 and 100 micron acceptable. Any finer and you are increasing the probability of clogging and the required maintenance un-necessarily.

    I agree paper filters should be avoided - most are far finer than 100 micron and can clog much faster and trap water much easier. It is beyond me why places like Aircraft Spruce even sell them.

    I would also never use a plastic or glass filter housing in the engine bay.

    If using electric fuel pump(s) many have a pre-filter built into the inlet (ala 914 Pierburg pump). If you have an electric pump chances are it has one and it may be required by the pump manufacturer - it is another maintenance item.

    If you have another type of fuel system - IE injected - follow the manufacturers recommendations to a tee. Many injectors require much finer filtering than a carbureted engine.

    Incorrect filter micron selection/maintenance may be the cause of some rough running installations. How many even know the micron size of their filters?

    All IMHO, YMMV!
    Greg

  5. #5
    Senior Member jiott's Avatar
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    Default Re: Fuel Filter Advice

    I use the filter provided in the factory SS7 FWF kit for the 912. It is a NAPA inline filter in a metal housing, mounted at the inlet to the fuel pump per the build manual. Finger strainers are also include in the outlet of each fuel tank.

    I personally don't believe a gascolator is necessary (neither does the factory) because you don't need to filter twice and the header tank with its drain at the lowest point in the system does the same job as a gascolator for water separation/draining.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  6. #6
    kitfoxnick's Avatar
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    Default Re: Fuel Filter Advice

    My setup is very similar to Lowell's. I have two glass filters visible through the turtle deck. These filters can be taken apart and cleaned. I like being able to monitor the fuel and contamination level.
    Nick W
    IV 1200
    912Ul
    Warp Taper Tip

  7. #7
    Senior Member
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    Default Re: Fuel Filter Advice

    Hi Jim,

    I personally don't believe a gascolator is necessary (neither does the factory) because you don't need to filter twice and the header tank with its drain at the lowest point in the system does the same job as a gascolator for water separation/draining.
    I know there has been a lot of debate on this topic. I suppose you could use the header tank for separation - assuming you include it in each pre-flight check for water. If not it is useless for that purpose. The outlet is near the bottom and so it would be prudent to check/drain regularly anyway.

    I also don't think the factory would be opposed to using a gascolator if a builder wanted to utilize one. As a point of reference - they are required in Canada.

    I guess if you've ever gotten water out of a gascolator you'd be in the believer camp - I'm a believer! Of course if you don't have one, it would be hard to tell until potentially to late.

    IMHO,
    Greg

  8. #8
    Senior Member jiott's Avatar
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    Default Re: Fuel Filter Advice

    You are right, I include draining a sample out of the bottom of the header tank as part of every pre-flight checklist. I also agree a gascolator is not going to hurt anything as a belt and suspenders approach, but it is another maintenance point to deal with. If you have a gascolator, I believe you should still also drain the header tank on a regular basis because it will separate water and that water will lay in the bottom of the tank up to the level at which the outlet fitting to the engine is located (about 1"). This can be a lot of water and if it is not drained, it could suddenly overflow into the engine feed line and possibly even overwhelm your gascolator. I believe in the KISS principle and prefer to drain preflight samples in just the 3 spots-header tank and 2 wing tanks.

    Some people say that a gascolator can be located at a lower point in the fuel system than the header tank, and I suppose this may be true on some airplanes. It also may be true on a tricycle gear airplane. Most of the water is going to separate during periods of sitting on the ground, and a taildragger like mine sits with the header tank drain being the lowest point, so I am very comfortable without a gascolator.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  9. #9
    Senior Member Dorsal's Avatar
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    Default Re: Fuel Filter Advice

    I also use the metal can filter and no gascolator,change the filter every 100 hrs.
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  10. #10
    Senior Member
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    Default Re: Fuel Filter Advice

    I generally agree Jim, but a question - do you think its possible with a taildragger sitting, that water could collect in the aft portion of a wing tank (behind the drain) and then in a level flight attitude, make its way through the fuel system?

    A few other points to ponder:

    In the old days - don't know if still true as I can't find recent stats - somewhere between 5 and 7 aircraft accidents/incidents a MONTH in the USA were caused by fuel contaminated by water. Of those, about 75% were attributed to pilot error. IE: inadequate pre-flight.

    So, I guess the point is - it really doesn't matter want gear you have in your craft, if you don't have a thorough pre-flight routine and stick to it.

    As an aside, some may wonder why aircraft with electric fuel pumps AND a return line don't generally use gascolators. The fuel is flowing too fast for a separator to function and as such the water generally stays in suspension and diluted enough so as to still be a combustible solution. This however, does not negate the need to do proper a pre-flight of checking for water in each fuel reservoir.

    Again IMHO,
    Greg

    Greg

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