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Two fuel tank thoughts. Am I crazy?

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  • #16
    Originally posted by 64osby View Post

    The 1/2" has a Cv of 3.1, or 3.1 gallons of water per minute with 1 psi differential between input and output. Relying on gravity and tank differential levels it would be.
    I very much doubt you’ll be able to get a 1psi delta between the 2 tanks, and you don’t mention how much pressure is required to open the check valve. I don’t think any spring loaded, pressure-operated valve will work. A cursory look at the McMaster offerings didn’t reveal any candidates, as far as I could tell.
    --Mark

    1973 SIII 109 regular w/2.5NA Diesel

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    • #17
      Possibly something like a larger size one of these flapper valves. They mention a 0.05psi cracking pressure, though they don’t say what’s required to get this valve beyond the point of being cracked:

      https://www.improvedracing.com/high-...eck-valve.html

      EDIT: The orifice in the male end of a “-12” AN fitting is only 0.61” in diameter, so even with the largest size flapper valve, it would probably take a while to gravity-fill one tank from the other.
      Last edited by SafeAirOne; 08-11-2022, 09:17 AM.
      --Mark

      1973 SIII 109 regular w/2.5NA Diesel

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      • #18
        I think the differential pressure will be .4 psi between a full and empty fuel tank, and a 1.35 inch or so difference in fuel tank levels should get you to 0.05 psi to open the shown check valve. There likely won't be much flow but if you want to prove the concept fab the setup using a check valve, hose and some tubing gooped to the bottom of a couple of 5 gallon buckets. Fill them with water to the depth of the fuel tank and drain from the supply tank. While water won't flow exactly the same as gas or diesel, you can see what happens.

        Bob

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        • #19
          Originally posted by 64osby View Post

          Positives that I see:
          1- Two tanks worth of fuel from one filler, no need to lift the seat on the drivers side
          2- No switch, no secondary lines, no separate pickup, no extra wiring, no separate sender unit.

          Any thoughts on this? Am I crazy?
          Yes -crazy. How many more failure points are you adding? How will you shield them from damage from something like road debris, branches or recap tire bits?

          The simplicity of the existing two tank system with brass changeover valve or simple electrical switchover like pick-up trucks use is handy. The ability to isolate one tank or the other for impromptu repairs etc. Sooner or later all tanks fail +-.

          People have plumbed in an electric transfer fuel pump to fill the auxillary tank from the main tank but that requires close attention to how much is in there and how much you are filling it with.

          Really the sole advantage is not having two fillers. Its a lot of rigamarole to avoid that.
          -Matt
          ------------------------------------------------------------------------------------------------
          A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away. ---Antoine de Saint-Exupery

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          • #20
            I did the military switch-over valve and have 1 filler per side in the tub original location and mirrored to the other side) .

            Pros, in addition to those others listed above, include:
            - It switches the electricity from the senders in addition to the fuel
            - It isolates the 2 tanks, such as for leaks as above, but also in event of fuel contamination
            - It is switchable on the fly - engine doesn't see an interruption in fuel. I know a connection between both tanks would work in effect the same; just noting it here

            If you go above the driveshaft with the line connecting both tanks, you could get an air bubble trapped in the line (maybe?)

            Mine is a diesel, so I had to decide how to handle the return line from the injector pump (plumbed to a single tank). Just connecting the 2 tanks at the drain plugs would take care of a potential issue with the changeover tap setup, as level is always equalized between tanks (except on a side hill, again as above).
            Miles
            1965 Series 2a 109 diesel soft top/pickup/3-door, Limestone

            Jesus rides beside me
            But he never buys any smokes
            --The Replacements, Can't Hardly Wait

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            • #21
              Originally posted by MilesBFree View Post
              ...so I had to decide how to handle the return line from the injector pump (plumbed to a single tank). Just connecting the 2 tanks at the drain plugs would take care of a potential issue with the changeover tap setup, as level is always equalized between tanks (except on a side hill, again as above).
              This is a good point. If at some point you decide to go fuel injection (Holley sniper kit, i.e.) wouldn't you also need to swap the return lines tank-to-tank, in addition to the supply lines??

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              • #22
                More info on Land Rover Fuel tanks

                https://pablanchard.co.uk

                josh t




                Attached Files

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                • #23
                  Originally posted by 50 wulf View Post

                  This is a good point. If at some point you decide to go fuel injection (Holley sniper kit, i.e.) wouldn't you also need to swap the return lines tank-to-tank, in addition to the supply lines??
                  Not necessarily. The main situation where you would have an issue is if the tank to which a single return line was plumbed was already chock-full. If you fill both tanks at the same time, switch the tap to draw first from the one with the return line.

                  An exception would be if the non-return line tank was full to the brim of really old fuel and you wanted to fill the return line tank and pull from the non-return tank first. As long as you manage the tanks you would probably be fine

                  And depending on the volume and pressure of the fuel being returned to the tank, type of tank, cap, etc., might need additional venting. This is a purely theoretical point, but something to think about.
                  Last edited by MilesBFree; 08-24-2022, 11:42 PM.
                  Miles
                  1965 Series 2a 109 diesel soft top/pickup/3-door, Limestone

                  Jesus rides beside me
                  But he never buys any smokes
                  --The Replacements, Can't Hardly Wait

                  Comment


                  • #24
                    The Ford electric changeover valves used to swap over the return lines as well I think? I always figured if I went diesel and needed two returns that would be the way to go. I think Pollack made them for Ford.
                    -Matt
                    ------------------------------------------------------------------------------------------------
                    A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away. ---Antoine de Saint-Exupery

                    Comment


                    • #25
                      Originally posted by Yorker View Post
                      The Ford electric changeover valves used to swap over the return lines as well I think? I always figured if I went diesel and needed two returns that would be the way to go. I think Pollack made them for Ford.
                      Yeah, Pollack has a dual tank/dual return electric valve. I've got one sitting in my closet waiting for me to hook up that long range tank to the fuel system on my 2.5NAD 109.
                      --Mark

                      1973 SIII 109 regular w/2.5NA Diesel

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