Air dryer odd purge every 5-10 seconds

Discussion in 'Freightliner Forum' started by W Bench Farms, Nov 13, 2021.

  1. W Bench Farms

    W Bench Farms Light Load Member

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    95 FLD120. Having an odd issue with the air dryer. Dryer will sometimes purge every 5-10 seconds. It's not a normal purge, it's a long release of air. Doesn't do it all the time. Seems to do it more when it's cold. Compressor will run up to 120 and then it will sometimes do it. Air pressure does not drop like I have a leak, it stays right at 120. I thought the issue was in the dryer, and the compressor has some miles on it and was leaking some oil, so changed the compressor and dryer. Thought that fixed the problem then started again. Replaced the regulator as I thought it may have some oil in it making it stick when cold. Helped some, but still having the issue. Seems like it will do it when running down the highway, pressure goes down to cut in on the compressor, and when it runs back up the dryer will purge steadily. But like I said it's a long release of air, not the normal quick exhaust. Anyone have this happen?
     
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  3. JonJon78

    JonJon78 Road Train Member

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    Maybe this will help...
     
  4. W Bench Farms

    W Bench Farms Light Load Member

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    I think I narrowed down my problem. The compressor has a safety pop off valve on the side of the head. This seems to be the source of the air purge. Sounds just like the dryer. Finally caught it in action, as it never seems to do it when sitting at an idle, and happens randomly. Usually only when it's cold, or cruising down the highway. Going to pick up a replacement tomorrow. Hoping this will be the fix.
     
  5. lilillill

    lilillill Sarcasm... it's not just for breakfast

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    It's the governor sticking that's causing the safety valve to pop, that is, if the pressure is also correspondingly high. Change the governor or lube that one up with a little silicone spray.
     
  6. W Bench Farms

    W Bench Farms Light Load Member

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    I'm thinking the blow off pressure on the safety valve is low. Compressor, governor, and dryer are all new. It was doing this with the old set up. The safety is the only thing I did not change. Pressure gauge goes up to 120 and the safety will go off. Doesn't do it all the time. It's going off just under the cut off pressure on the governor as when it does this, the safety will purge several times then the dryer will purge, and then it's fine for a while.
     
  7. lilillill

    lilillill Sarcasm... it's not just for breakfast

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    The new compressor didn't come with a new safety valve? If it's popping off at 120, then yep, time to replace it.
     
  8. W Bench Farms

    W Bench Farms Light Load Member

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    New compressor didn't come with one, and I should have replaced it, but it was a Sunday when I had it off so no luck getting one. After doing some research, Bendix makes 2 different versions. A 1/2" NPT 250 psi and a 1/4" NPT 250 psi with a bushing. Someone had replaced this one before with a 150psi. Hoping this is the issue.
     
    lilillill Thanks this.
  9. W Bench Farms

    W Bench Farms Light Load Member

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    New safety pop off valve did the trick. Ran all day today and all is well.
     
    lilillill and Crude Truckin' Thank this.
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