Trailer air supply line pressure? I have a supply problem

Discussion in 'Volvo Forum' started by 86scotty, Jan 7, 2023.

  1. 86scotty

    86scotty Road Train Member

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    If you mean trailer protection valve then yes.

    It's a 2015. It has 3 valves at the tank. One is brakes and brakes are fine. Never had a problem with brakes at all. Another controls tire inflation (replaced yesterday) and another controls tandems and leveling valve (replaced it too yesterday). Also replaced leveling valve yesterday which I can't calibrate because I can't get air to it reliably.
     
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  3. wichris

    wichris Road Train Member

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  4. 86scotty

    86scotty Road Train Member

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    My understanding is that that is the brake valve, the big center one on my tank looks like that. Are you saying you could control leveling valve and other things as well?
     
  5. wichris

    wichris Road Train Member

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    The big one with the ABS cables is the service valve. The one pictured is the emergency valve. Air goes through it to the tank, if it's sticking (one side) the brakes will still release.
     
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  6. D.Tibbitt

    D.Tibbitt Road Train Member

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    If you can find where you are losing that air supply . you should be able to narrow down where the problem is at. It almost sounds as if there is a blockage somewhere. Maybe a piece of debris inside the lines or a kink. Im not sure testing pressure at the gladhands would tell you much because it sounds more like a flow problem than a pressure problem... Although a simple way to check pressure would be to use a spare gladhand and find a air pressure gauge with male threads that can thread into the female side of the glad hand then connect glad hand to the red gladhand on the truck side. (Like ur hooking up a trailer or like ur hooking up a gladhand tire inflator hose)....

    But if the brakes work fine as well then i wouldnt think it would be a tank problem either because all that air to the brakes is supplied from the trailer tank... There has to be a blockage on the supply line somewhere. It is either in the valves itself or in the line... And if u have replaced all the valves then it has to be the lines... I think if it is supplying air to the tank at a normal rate when u press the brakes and bleed it down, the problem is most likely after the tank itself.. Maybe a piece of rust inside the tank has made its way into the supply lines to airbag and leveling valve... Something as simple as unhooking the leveling valve airline and supplying air pressure to the lines (pressing in red knob, make sure wheels are chocked)may be enough to clear the blockage if their is one....

    Just thinking out loud here. Hopefully this can help u a bit. Let us know what u discover
     
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  7. Big Road Skateboard

    Big Road Skateboard Road Train Member

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    Didn't read all, but you did check the pressure protection valve? Should be in the left or right end of the tank.
     
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  8. Stringb8n

    Stringb8n Road Train Member

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    Pass through valve? I had a similar issue. Could hear air hissing under hood sometimes, would hear it in the tube that runs under the cab. One time the brakes didn't wanna release on the trailer I'm assuming, but that was only once before I had the pass through valve on the firewall replaced. My shop I go to charged me I think $213 for the part, have to look to see what they charged for labor.

    I could hear air through the valves on the dash though, for a short while after starting the day then it would go away. Now I only hear it long enough to charge trailer tank and no more air noise.
     
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  9. D.Tibbitt

    D.Tibbitt Road Train Member

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    Curious to find if you ever figured out the problem
     
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  10. 86scotty

    86scotty Road Train Member

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    Sorry for the suspense. It's been a long week. WiChris nailed it, it is the emergency valve, aka spring brake valve, on the tank. I finally found the right part yesterday at Fleetpride. I left out Sunday night with a scheduled run to Boston and back and had to just wing it and haven't had time to update here. I drove for half a day with empty airbags but it was a light load and a frustrating couple of days. Eventually I got it working.

    But, it wasn't just that valve. My leveling valve was shot and leaking and I think both other pressure protection valves on my trailer tank were gone too. One issue kept fooling me for another issue. I was convinced last Sunday that the problem had to be supply from the tractor, which would point to tractor protection valve (where air lines come off back wall of tractor) but when I attached a gauge to my red glad hand I got 120 there so that ruled that out.

    Anyway, I'll report back one more time after I'm 100% sure it's fixed but I'm pretty positive the slow supply to trailer is from a bad emergency valve.

    I haven't put a lot in to this moneywise and feel alot better knowing all this stuff is updated and now I understand what lines go where and what controls what. Two pressure protection valves, emergency valve and leveling valve probably $250 total.

    One thing I did that some folks might consider is I added a female air coupler to my air tank. I did this primarily so I could plug an air gauge in to it to monitor the pressure in my tank while I figure out this problem but the long term win is I have air at the rear tank. In other words I can run an air hose/air tools or whatever from my trailer tank now.
     
    Last edited: Jan 12, 2023
  11. D.Tibbitt

    D.Tibbitt Road Train Member

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    If u still have the old leveling valves , dont throw them away unless you end up stripping out the hex bolts that hold the cover togrther. You can rebuild them. If you open it up there is a couple of o rings inside that go bad then it leaks air.. Replace o rings then u have a new leveling valve or atleast one to keep as a spare... Theres a metal plate inside that is what opens and closes the different valves to control air... Make sure to put it back on the same way or it will reverse your air flow... Meaning the airbags will deflate when its supposed to go up and inflate when supposed to go down... Safe travels thanks for the update
     
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