Air release from compressor safety valve.

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by dberset, Mar 26, 2023.

  1. dberset

    dberset Bobtail Member

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    2016 Coronado glider, 12.7 Detroit series 60, bendix truflo 550 compressor.
    This has been a persistent problem for a couple years now. Late last fall I decided to finally dig in to correct it. I was hearing an intermittent whistling noise but had no clue where it was coming from.
    I thought it might be a boost leak so I cleaned boost hose connections and used new clamps And checked CAC for Leaks, No luck.
    One day I realized driving across Texas that it only whistles under load, moderate boost, at just below 100psi on my air gauges(cut in pressure), and air pressure will not rise while whistling.
    If you lift your foot and let the boost fall it will stop whistling and start building pressure. That definitely led me to the safety valve.
    I stopped at freightliner and bought a new valve but still had the problem. I also used a solid plug temporarily In place of the valve to make sure it was the valve and it did not whistle.
    Replaced governor. No luck.
    Then replaced the discharge hose believing I’m dealing with a restriction. No luck.
    Then onto the dryer. No luck.
    The day after Christmas, I spun the rear main bearing(-24f) and have since replaced the engine with a complete reman which included a new/rebuilt compressor and governor so those are totally eliminated.

    As of Today, that’s as far as I’ve gotten with it with the check valve being the next possible(maybe) restriction in line.
    Is it possible for the check valve/s to be restricted? The old compressor with 833k on it did pass a little oil so could the check valve/s be coked up from oil?
    Also there is plenty of air pressure coming from the tank line at the governor and I blew shop air through the line from the governor to dryer with no problem.
    I’ve called a couple of shops and nobody has ever encountered anything like this.
    Am I heading in the right direction as far as a restriction or not?
    Operation of the truck isn’t a problem, I still have plenty of air pressure but I know the safety valve should not be leaking.
     
    Last edited: Mar 26, 2023
    Rideandrepair Thanks this.
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  3. JB7

    JB7 Medium Load Member

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    What do the dash gauges read for pressure, is the system building to over 120psi? Do you have one of the newer style driers such as the Bendix AD_IS with an electronic control module? Calling a shop and asking questions and taking it in for repair are 2 completely different things. The safety valve is set to pop off at 150psi. You are saying that the whistling sound is coming from the valve? If so, it is relieving excess pressure.
     
  4. Rideandrepair

    Rideandrepair Road Train Member

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    New compressor and gov. Reused the check valve? I had one leaking on my Truck. Same compressor/governor. Probably different air drier. It would barely seep. Eventually got weaker and would pop off for no reason. I wonder if yours has the same valve as mine. Might need a higher psi rating? Try vin# A 10466. That’s for a 99 Classic. See it it’s the same valve. As I recall it’s rated much higher than 150. I could be wrong. I’m guessing they used a new silicone hose from intake to compressor. If not, make sure it doesn’t have a small hole in it. It’s in a very tight spot on the back of compressor. It’ll cause a whistle and boost leak, hard to detect, till it finally completely blows out. They get chafed and can’t be seen, because of its location. Also exposed to a lot of heat at the compressor and are prone to getting weak.
     
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  5. Goodysnap

    Goodysnap Road Train Member

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    Those relief valves almost always pop off way above 150. Plumb a gauge in. If it is In fact high and still popping off you have a restriction between the compressor and the dryer.
     
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  6. JB7

    JB7 Medium Load Member

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    The relief/safety valve I refer to is in the air tank which is after the drier. It relieves excess tank pressure. Yes, plumb a gauge in. How is a restriction between the compressor and drier going to cause high air pressure in the tanks which are after the drier? The restriction you mention would cause high pressure before the drier, not after. Even if there were a restriction between the compressor and drier, if everything is connected correctly, the governor would/should shut off the compressor before the relief valve popped off.
     
  7. Goodysnap

    Goodysnap Road Train Member

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    I may be incorrect. I assumed the OP was referring to the pop off in the compressor head? No?
     
  8. dberset

    dberset Bobtail Member

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    Gauges read normal. Cut- In just below 100psi cut-out right at 120psi.
    Ad9 dryer. Simple old school.
    Most shops I’ve been to don’t diagnose anything. They just spend your money. plus I could never replicate the problem. It’s totally random.
     
  9. dberset

    dberset Bobtail Member

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    Last edited: Mar 26, 2023
  10. dberset

    dberset Bobtail Member

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    Can’t be a restriction between compressor and dryer. The discharge hose is new along with the dryer.
     
  11. dberset

    dberset Bobtail Member

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    I am referring to the safety valve on the compressor head.
     
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