Page 1 of 2 12 LastLast
Results 1 to 10 of 22

Thread: Small but steady air leak

Hybrid View

  1. #1
    Join Date
    Apr 2008
    Location
    no where
    Posts
    439

    Default Small but steady air leak

    Well after 6 years and no air leaks to speak of, I have my 1st air leak that I can not find.

    Symptoms:
    1. Key off
    2. Level low in drive position
    3. parked on a level spot
    4. Air bags holding air, NO LEANS
    5. Primary and secondary air gauges lose about 1.5 lbs an hour.
    6. They will eventually go down to zero over a period of 3 days or so.
    7. They go down in sync. Both primary and secondary seem to lose air at the same rate.
    8. Aux Air guage goes down to about 70 Lbs and holds there.

    I have sprayed soapy water all over the air tanks, their fittings and drain valves with no luck. I have to believe that since both tanks are going down at the same rate that there must be something in common with both that I need to check.

    I am thinking that it could be:
    1. Air compressor ?
    2. Air governor which I have been unable to find...??
    3. Air dryer?

    Any others I should look at? And how do I test the above 3 components?
    It is a very small but persistent leak and I may have to wait until it gets bigger to find it, but I don't like that idea. What makes me frustrated about this leak, is that until now the primary and secondary air gauges NEVER lost so much as a pound over weeks or months. Those gauges were rock solid at whatever pressure was on the system when I shut down the bus.

    Any ideas where to look?

  2. #2
    Join Date
    Aug 2006
    Location
    Houma, LA
    Posts
    1,783

    Default

    Andre,

    I think I can help you find the air governor. Locate the starter and the starter solenoid on the starboard side of your engine. There should be an 1/4" air hose close by. Follow the air hose traveling toward the back of the coach and you will find the air governor.

    My air governor crapped out while I was dry camping. Next morning when I started the engine it would not go in gear. I checked around the air governor area and sure enough I could feel an air leak.
    Tuga & Karen Gaidry

    2012 Honda Pilot

  3. #3
    Join Date
    Dec 2010
    Location
    Penetang
    Posts
    117

    Default

    Andre,
    I'm sure you already know where to find pneumatic diagrams for your coach, if not go here http://prevostparts.volvo.com/techni...neumatique.asp
    The placement of the valves and check valves should help you isolate the leak. Air valves are clearly indicated and check valves are identified by an arrow. I would doubt that it is the compressor unless the check valve has failed.

  4. #4
    Join Date
    Jan 2006
    Location
    anytown
    Posts
    8,908

    Default

    Andre,

    Following up on Lee's points You gave some significant clues. Your leak relates to the braking system only or primarily. If the primary and secondary gauges are dropping the leak is somewhere between the compressor and the valves that actuate the brakes.

    You can rule out anything relating to the brake chambers because when parked there is no air to them. Air to the chambers stops at the relay valves. So by isolating your quest to those devices from the compressor through the entire system up to the relay valves you are likely to find the leak. Lee is correct that the pneumatic diagram will help you with where to look.

    FWIW 1.5 PSI per hour is a very small leak. The fact that both systems leak down the same rate look for points common to the secondary and primary. Brake treadle? Air dryer? Check valves, especially at the compressor? In a perfect system you should be able to drain air from each air tank in order and still have pressure on the next one.

  5. #5
    Join Date
    Jan 2011
    Location
    Cincinnati, OH
    Posts
    23

    Default

    I have this same problem on my new coach. I logged on to do some searching for answers. Mine is a slow leak and both primary and secondary go down at the same rate. Thanks for the help.

  6. #6
    Join Date
    Jan 2006
    Location
    anytown
    Posts
    8,908

    Default

    For anyone who has not yet chased air leaks, or who is new to the Prevost attempting to find every leak and repair them all becomes a frustrating obsession. I have no idea how many air fittings we have, how many potential leaks we have, or how to stop the aging process on the rubber components used to prevent leaks.

    What can be said is if you have leaks and you turn your coach over to a service center or mechanic to fix them it is going to get expensive. I am not suggesting you ignore leaks, but like Andre, you provide detailed information about the characteristics of the leaks to help a knowledgible person to isolate the area to be investigated. If the mechanic understands the coach, and the information provided is accurate the effort required is minimized. Those of us who have chased leaks know there is no single best way, or easy way to find them. The big ones are easy because you can hear them. The smaller leaks, especially those in inaccessible places are much more difficult to find. So far I know of six ways to detect leaks. We can listen for them. We can use a soapy solution. We can use a stethoscope. We can use an ultrasonic leak detector. We can use Freon to pressurize the system and then use a Freon leak detector (use caution here). And finally we can use a device Hector will show during a seminar in Austin in October that allows bubbles in water to signal a leak in a circuit.

    Each method has its positive and negative aspects, and for the determined owner the use of them will eventually identify every leak. If the owner turns the responsibility over to someone else there is a financial aspect to leak detection and some owners have spent thousands chasing perfection.

  7. #7
    Join Date
    Nov 2007
    Posts
    285

    Default

    Here is Eric/Deb Faires suggestion. On our 92 Angola, we had a leak from the fitting at the actual gauge on the dash. Where the gauge was fastened to the air line, that's where we had a leak. Replaced the little fitting, that leak ended. Would surprise me that both gauge fittings/connections would go at same time, but might be worth a look. Was fun experience removing the dash to look behind it to see lots of wires for the first time.

    Eric and Debbie Faires
    Huntsville, TN

  8. #8
    Join Date
    Aug 2010
    Location
    Lead, South Dakota
    Posts
    37

    Default

    My bus had a leak that was taking all three air tanks down to zero in 4 hours. I had been chasing this leak for 7 months and the bus had been to three different shops and to Prevost Jacksonville twice. One shop stated correctly that a leak that large should be able to be heard but it wasn't. Once the bus was at Prevost Jacksonville I decided to change the tires and when the bus was up on the lift it stopped leaking. This gave them an initial clue as to what the problem was. They split the systems by isolating the converter side from Prevost's side and finally changed the R14 valve which fixed the issue. This leak had perplexed pretty much everyone and proved very frustrating. To Prevost's credit the second time the bus went into the shop they credited to work as "rework" and there was only a limited charge. Hopefully my experience will help someone else. Cheers

  9. #9
    Join Date
    Apr 2008
    Location
    no where
    Posts
    439

    Default

    Update.

    Last Thursday I received the electronic stethoscope from Truk in the mail. I did not have time to use it Thursday night, and Friday I took the coach on a short trip to get a bad valve stem replaced on a tire. When I got home, I put the bus up Jon's stands and built air pressure up until the air dyer spit. Then shut the bus down. So I planned on spending Saturday morning under the bus looking for my air leak. Well, it is now Thursday and it has not lost a single pound of air since last Friday! With no leak, testing never happened. So, I am reluctant to send Truck his stethoscope back, knowing as soon as I do, the leak will reappear.

    On a more serious note, what should I suspect now? I am sure the leak will reappear at some point. I am thinking a Norgren valve, maybe a spool valve did not close in the right position? Any suggestions of the most likely place to look the next time the leak appears? I really hate these types of problems.

  10. #10
    Join Date
    Jan 2006
    Location
    anytown
    Posts
    8,908

    Default

    Andre,

    I am not familiar with the Royale aux. air system but in your original post you spoke of a slow leak in both brake systems, and perhaps a larger initial leak in the aux air.

    You have to mentally separate the two air systems and focus on one or the other. Yest they come from the same air compressor, but beyond where the aux air is supplied they never rejoin. Leaks do not repair themselves so if it had a leak, if will again leak, but chasing a slow leak is frustrating, and chasing a leak not currently present goes way beyond frustrating.

    I suggest you anticipate the leaks showing up again, and eventually getting worse, but to relax until they are more serious. Then gather the tools, ears, soapy water, stethoscope, etc and prepare to do battle, but first study the air systems so you can take the clues the bus provides and concentrate your search efforts in areas likely to be the leak source.

    Air leaks are the biggest annoyances we have relating to bus ownership and even if you do like Hector did and like I did once and got a leak free coach, it would not be long before leaks reappeared. I have moved past worrying about stuff like that until they get to be more serious.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •