Fuel tank sealer

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by fulcona, Dec 15, 2018.

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  1. Dec 15, 2018 #1

    fulcona

    fulcona

    fulcona

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    I'm about to build a custom fuel tank that will mostly use auto fuel. Ethanol free fuel is available, but still is a concern. Of course a welded aluminum tank would be ideal, and still possible, but a composite tank would be easier (and cheaper) for me. Lancairs,etc use a Jeffco sealer (expensive) but I don't need the amount sold by Aircraft Spruce (3gal.) so my question is, would it be possible/prudent to "skin" the entire inside of my composite 22 gallon tank with Proseal as is used on the seams of RV tanks? This would appear to be a cheaper alternative to the Jeffco option.
     
  2. Dec 15, 2018 #2
  3. Dec 15, 2018 #3

    BJC

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  4. Dec 15, 2018 #4

    wsimpso1

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    Proseal on Fiberglass? It might work over the long haul. I have two options that I KNOW will work long term as a complete protection against gasahol.

    Build the tank using vinylester resin instead of epoxy. Make pastes from yinylester for bonding too. This is my preferred choice for new construction of fuel systems. Vinylester is proof against ethanol bearing fuels, and is only a little poorer for both handling and strength than epoxy. You might need to make a couple practice parts before you commit to your tank pieces. Use only fresh material with vinylester - it does not like the shelf;

    Build the tank with epoxy and then seal with Flourosilicone sealer from Dow - Silicone Primer is PR1200, then coat that with Dow 730 FS. This option is only preferred if you already have the tank built.

    The primer comes in various size containers, is water thin, and can brushed or sloshed. 730 FS is pricey stuff, but over PR1200, it is solid and proof against ethanol. Because it is so pricey, you do not want to buy much of it. For tank sealing, it comes as a paste and you disperse it in lacquer thinner for application. Dow sells bigger containers of it and folks do thin for application, they recommended that for me too. I made it a little paint-like for brush application. I applied the primer, let it cure per the instructions, then applied sealer to all surfaces I could except the faying surfaces for bonding things together. After bonding the pieces together, I sloshed it all with primer, let it cure per the instructions, then thinned my sealant with enough lacquer thinner to make it slosh well. Captured it in steel paint cans between uses and none of the materials went bad over a month or so, but these are air cure silicones, so do not buy or open more than you need at one time. One issue I had was that my parts were porous, and weeped primer the first time they were sloshed. A couple more cycles of sloshing with primer filled the porosity, then sloshed with sealant. It seems to work...

    You might do well to have ports in the tank so you can reach inside and seal the whole thing once it is together. Ellsworth Adhesive is a good source for the materials.

    One look at the prices, and I suspect you will just figure out how to make the tank with yinylester resin.

    Billski
     
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  5. Dec 15, 2018 #5

    TFF

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    Use the Bill Hursh stuff. I have only used it in cars, but it is similar to certified airplane stuff I have used on FG tanks. Pro seal on an RV is only for the seams.
     
  6. Dec 15, 2018 #6

    wsimpso1

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    The best question so far is that one right there.

    For the sealer to work on a fiberglass tank, it has to do three things:
    Seal up porosity and the surfaces;
    Stay put in a continuous film forever;
    Prevent ethanol from diffusing through to the resin of the tank.

    The usual products for sealing up a porous tanks may be good at filling porosity and staying put in gasahol, but do they keep the ethanol from diffusing through to the tank resin and damaging the tank? You must ask that question and get an unqualified "yes" on preventing ethanol migration. That was why Dow 730 was such a good choice - it prevents ethanol diffusion and so can protect underlying fuel sensitive materials. The other stuff on the market when I did this did not pass muster. Maybe some newer stuff does, but check before you buy.

    Billski
     
  7. Dec 16, 2018 #7

    BBerson

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    Line the inside of the composite tank with thin aluminum sheet. Then pro seal the corners.
    Or make it out of thin aluminum sheet with pro seal on the joints, then layup glass on the outside to make it stiff.

    (I haven't tried it)
     
  8. Dec 16, 2018 #8

    dino

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    I applied the second product (Bill Hursh) as a sealer on an EZpoxy-Rohacell sandwich gas tank. Anecdotally, EZpoxy is gasohol proof so the sealer was slosh applied as insurance. It is a milky, one component product that is easy to apply but I haven't used the gas tank yet so can't report on results.
     
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  9. Dec 18, 2018 #9

    proppastie

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    I would be careful of a product that says "resistant".....How much resistant?
     
  10. Dec 18, 2018 #10

    Pops

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    I have use it, no problem.
     
  11. Mar 10, 2019 #11

    TJay

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