2002 Volvo VNL 780 Air PSI Issue

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by JRK, Aug 1, 2021.

  1. JRK

    JRK Bobtail Member

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    Feb 18, 2016
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    picked up truck after having it serviced a
    2002 Volvo VNL 780
    VIN 4V4NC9TJ12N331024
    Engine serial ISX 475HP 14020915
    shop is closed had to drive home with this, there is 115 psi in air tanks , breaks release, air to suspension.
    No Air to Splitter or Cab air bags or to raise or lower suspension or engage rear differential.
    any help would be appreciated.
     
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  3. AModelCat

    AModelCat Road Train Member

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    Sounds like the pressure protection valve is sticking. Probably located on one of the air tanks.
     
    spsauerland Thanks this.
  4. Team818

    Team818 Medium Load Member

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    I hope he can correct that. Wow. The mechanical forces released that Truck to soon. My goodness I hope its doesn't cause a incident on the highway. Might want to U Turn and get back there asap, what if the brakes all apply at the same time..... yikes.
     
  5. JRK

    JRK Bobtail Member

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    i have never heard of that what does it look like
     
  6. AModelCat

    AModelCat Road Train Member

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    Purpose of the pressure protection valve is to protect air supply for the brakes. All it is is a valve that won't let air flow from the tanks to the air operated accessories until a specific system pressure is reached. Ever notice how once a truck hits about 90 PSI the cab and suspension inflate? That's the pressure protection valve opening.
     
    spsauerland and Goodysnap Thank this.
  7. JRK

    JRK Bobtail Member

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    i didnt know till i was on the way home , no place to turn around. made it home safe and put truck in the air i thought tech may have disconnected or some thing came lose by accident.
     
  8. AModelCat

    AModelCat Road Train Member

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    Google search " Bendix pressure protection valve" there's a few variations that look different.
     
  9. JRK

    JRK Bobtail Member

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    i have heard of tractor protection valve, i had air to brakes and all air bags just not cab bags suspension and splitter, it is a 13 speed
     
  10. Team818

    Team818 Medium Load Member

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    Oh thank the Lord. It made it to your place.
     
  11. JRK

    JRK Bobtail Member

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