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FLD 4th air tank

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Trugo, Mar 25, 2019.

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  1. Mar 25, 2019 #1
    Trugo

    Trugo Light Load Member

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    Is anyone familiar with a 4th air tank on a feightliner FLD? This tank has only one hose connected and holds air. Is it safe to remove? Purpose?

    Also, would I expect my trailer air supply to come from the wet tank, or the primary tank?

    air noob here, trying to learn more.
     
    Trugo, Mar 25, 2019
    Trugo, Mar 25, 2019
    #1
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  3. Mar 25, 2019 #2
    Working2party

    Working2party Medium Load Member

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    EB150B08-D4DF-41AF-A939-B9204B4C92F2.jpeg
    Here is a basic air system diagram. If needed Antilock brakes, roll stability, Automatic Traction Control; Control this system with modified or inline added valves but still have to follow this basic schematic.

    All air operated accessories come off the secondary system with a 60-70 psi pressure/ check valve. (Meaning until the system pressure is above the threshold, the air won’t pass)

    So there’s an air system but shell.
     
    Working2party, Mar 25, 2019
    Working2party, Mar 25, 2019
    #2
  4. Mar 25, 2019 #3
    Trugo

    Trugo Light Load Member

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    That’s a good diagram. So, the trailer air tank supply comes from both primary and secondary tanks via the double check valve. Is this correct?
     
    Trugo, Mar 25, 2019
    Trugo, Mar 25, 2019
    #3
  5. Mar 25, 2019 #4
    AModelCat

    AModelCat Road Train Member

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    4th air tank. Is it smaller than the rest? Might be a purge tank for the air dryer. Trace the line and see where it leads. Might give us a better idea.
     
    AModelCat, Mar 25, 2019
    AModelCat, Mar 25, 2019
    #4
  7. Mar 25, 2019 #5
    Trugo

    Trugo Light Load Member

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    Yea 4th tank, not smaller it’s the same size as the wet tank. I’ve heard of another guy with an fld who has a 4th also. The Truck is in for the annual inspection so I can’t take a look. But I tried to trace it before, it would be hard without some disassembly. Air dryer purge hey. Maybe although my ad9 purges directly below.

    The truck has 3 tanks behind the cab, the wet tank, the secondary tank (small) and then this mystery tank with only one hose. The primary tank is behind the 5th wheel. I think that’s how it works anyway.
     
    Trugo, Mar 25, 2019
    Trugo, Mar 25, 2019
    #5
  8. Mar 25, 2019 #6
    spsauerland

    spsauerland Road Train Member

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    Drain each tank one at a time and watch your gauges is easy way to tell.
     
    spsauerland, Mar 25, 2019
    spsauerland, Mar 25, 2019
    #6
    SAR, BoxCarKidd and Trugo Thank this.
  9. Mar 25, 2019 #7
    Trugo

    Trugo Light Load Member

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    Ok good idea
     
    Trugo, Mar 25, 2019
    Trugo, Mar 25, 2019
    #7
  10. Mar 25, 2019 #8
    RustyBolt

    RustyBolt Road Train Member

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    With only 1 line going to it, sounds like just extra capacity to me. Would make the compressor work less.
     
    RustyBolt, Mar 25, 2019
    RustyBolt, Mar 25, 2019
    #8
    BoxCarKidd and Trugo Thank this.
  11. Mar 25, 2019 #9
    Trugo

    Trugo Light Load Member

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    Makes sense. So it makes it a double size wet tank.
     
    Trugo, Mar 25, 2019
    Trugo, Mar 25, 2019
    #9
  12. Mar 26, 2019 #10
    BoxCarKidd

    BoxCarKidd Road Train Member

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    No. If you need secondary air it cannot pull off the primary.
     
    BoxCarKidd, Mar 26, 2019
    BoxCarKidd, Mar 26, 2019
    #10
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