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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    I've had an occasional problem for awhile with my airbags and sliding tandem not working all the time, slow to build pressure. I replaced pressure protection valve and leveling valve in trailer today but still have a problem. I am getting pressure to everything in the trailer but not enough for everything to work reliably.

    Any idea what the pressure coming from the airlines at glad hands should be? I'm going to rig up a gauge to a glad hand tomorrow morning and test what I've got.

    I'm thinking the big valve on the firewall may be bad. I don't know what it's called. Has big green and red lines coming out of it, the green one goes straight under cab to trailer air line manifold at back wall. I'm thinking it's bad because if I supply air to the trailer and pull my red air line it just hisses, it does not pop closed on the dash as it should.
     
    D.Tibbitt Thanks this.
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  3. loudtom

    loudtom Road Train Member

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    This part?


    If you've got another trailer you can test on, it would help narrow down if the problem is with the tractor or not. I've had a valve get plugged up with debris on the trailer tank that made it take forever to build enough air to release the trailer brakes.
     
  4. 86scotty

    86scotty Road Train Member

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    That's the valve I am thinking of but he says that is the foot valve. I have no problem at all with brakes, I have a problem with air supply to the other things in the trailer (tandem release, tire inflation and airbags). I have replaced all valves in the trailer and checked and double checked them.

    Oh, by the way, I don't have any backfeed coming out of the foot valve like in the video.

    Any idea what valve I should check next?

    Also, I don't have a spare truck or trailer. I'd do both if I did, connect another truck to my trailer and another trailer to my truck.
     
  5. wichris

    wichris Road Train Member

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    Regulator on the air tank. That controls the leveling valve, air release, PSI, ect
     
    EverLuc Thanks this.
  6. 86scotty

    86scotty Road Train Member

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    Just replaced and chased all that down yesterday. I am not getting enough pressure to supply that regulator/regulators. Or I should say I am but only intermittently.
     
  7. Ridgeline

    Ridgeline Road Train Member

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    Check the pressure at the gland hand at the back of the cab and see what it is, if it is operating pressure, then look at a problem with the airline on the trailer. I had one which the driver ran over some junk on the road and and a piece of junk actually wedged up under the trailer and kinked the line, the mechanic had to replace that section of line.

    EDIT - didn't see the latest post, but it still is good info so I'll leave it.
     
    Siinman Thanks this.
  8. 86scotty

    86scotty Road Train Member

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    @Ridgeline, thanks, I went over and over the trailer yesterday. I've got to rig up a gauge to test air pressure at glad hands. I do know that I might have two problems. If I supply air to the trailer (red knob in) and yank it loose my red knob on dash does not pop, just constant rush of air from red air line. I know this is a problem, I just don't know if it's the only problem.

    I'm going to rig up a gauge this morning. A friend also suggested taking my air compressor to the trailer and supplying trailer with it to see if everything there is working.
     
  9. 86scotty

    86scotty Road Train Member

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    And also, what should supply line pressure at glad hands be, 120?
     
  10. wichris

    wichris Road Train Member

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    Whatever your tractor tank pressure is.

    You replaced the emergency valve on the trailer?
     
  11. Cat sdp

    Cat sdp . .

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    Is it a older trailer?Did you replace the diverter valve on the trailer ? Sometimes they get filled with crud and restrict air supply to trailer.Where the line goes back to the tandems and then all the other lines come out of the valve going to everything else at the back of the trailer.
     
    Siinman Thanks this.
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