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Strange “BIG” air leak
Last night, I stopped at Cracker Barrel just after dark. I shut the bus down, got out and walked to the rear to check on a hotrod I was hauling on a trailer. Before I got half way back, I heard a loud BIG air leak (and I don’t hear real well anyway), it sounded like it was coming from inside the tag axle tire, but I knew it wasn’t the tire itself because I had no warning on my Pressure Pro Pulse system before I got out. I looked around with a flashlight, and couldn’t determine the leaks exact location. I also noticed no decrease in air pressure before I shut down either.
Being cold outside, and mainly because I was hungry, I decided to go in and eat, and worry about it after dinner. When I came back out, I could barely hear a small leak, so I went in the bus to look at the gauges. Primary and secondary brake pressure was still at 120. The aux pressure was at 5 lbs!
I started the bus up to see how long it would take the aux air to build up, and it built up to 120 within a minute. I then could not hear a leak with the engine running, so I decided to head home. After I got on the Interstate and got the cruise on, I noticed the aux pressure was down around 110 or so. And while I was looking at the gauge, the needle quickly jumped to 120-125, as if a valve was stuck or something. It stayed right on 120 as usual for the rest of the trip home.
Ride height was normal, no sagging or leaning.
I parked the bus in the garage, and with everthing shut down,……..there was NO leaking! I went out this morning, and all 3 gauges were around 120 still.
So,, what happened? Maybe the air dryer pop off stuck?
Any other ideas or anyone had this happen?
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26 Replies
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You can rule out the air dryer because if the purge valve was stuck open it would not affect the accessory pressure and it is not near the tag, but ahead of the drive axle.
There are some accessory items in the area you describe such as the 3 Port Norgrens on the frame that open to atmosphere when the tag axle lift is employed. Did you lift the tag for a tight turn at the Cracker Barrel?
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I had the very same issue. Jeff looked at it when I was there a few weeks ago and said that the dryer has a valve which doesn’t allow the pressure to go above a certain psi, and will purge air when over that psi. My air purging stops about 30seconds after shutting down the bus. No other issues noted.
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No Jon, didn’t lift the tag at Cracker Barrel. I did lift it a few days before, and did when I got home. Not leaking still, so guess I’ll have to wait till it does it again.
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like for a air flush toilet or sliding door? a tiny bit of dirt can dislodge itself after a few cycles. The aux system (air) should have a seperate water seperator in steering compartment are. I know noise is not there— but you could have a little moisture there causing a valve to stick. Think aux side only as that seems to be gauge indicated culprit.
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Could be, guess I should have dug deeper while it was leaking, but had no way to get under bus at the time.
Can’t fix now because I can’t duplicate. No moisture in the system though……..we haven’t had rain in 46 days!
On the trip, I did hear the air dryer working though.
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Jerry,
If it ever happens again the starting point is to try to pin point the area it comes from. The fact you heard it outside and in the area of the tag axle is a huge clue that suggested the 3 port Norgren on the frame. The fact it was accessory air was another huge clue, ruling out other things in that area such as relay valves.
I cannot think of any converter installed accessory air devices that might be located in that area so without getting beneath the coach you can play with the tag axle lift valve or manually operate the level low to help focus on the problem.
I did not ask, but when the accessory pressure went down did anything else catch your eye such as the rear settling down?
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Jon,
No, nothing else was unusual, bus stayed at ride height, no sagging or leaning at all. I looked at that close. I had just left a big car show swap meet and traveled about a 100 miles when I stopped. While I was parked at the car show, I leveled the bus manually with the level low? Maybe that triggered something.
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I don’t think going from the manual level low to ride height had anything to do with the leak. And since the bus stayed at the ride height my theory about the 3 port Norgren is off the table. I don’t know enough about your conversion to know if the converter has something in that area that would leak down the accessory system. If the sound came from the passenger side there is a Prevost installed valve, manifold and I think a pressure regulator behind the tag and that might be something to look at.
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I had my tag brake relay valve stick and caused a major air loss. By the time I got a new one and it installed it quit leaking. I opened the old relay valve and did not see anyting unusual. Maybe yours was leaking like mine. My tag relay is located just above the tag axel.
I attached my phone to a stick and used the video camera to track down the leak without needing to get under the coach.
Dan
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If one of the relay valves was leaking the brake system pressure(s) would have gone down but they did not so the dilemma and its cause has to be on the accessory side. The problem is the coach and converter both use accessory air so the challenge is more complex.
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oops – missed that bit of info – my bad.
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Dan, excellent idea on the stick phone! I use mine from time to time to take pics in remote areas of the bus, but haven’t thought about a stick to reach further in. Maybe I need one of those Selfie sticks?
Jon, on my Featherlite, removing the fender on the pass side is nothing but 8 house batteries. On the drivers side above the axles is all the norgrens, and I think the valve you are talking about may be moved to the pass side by Featherlite.
The leak was so loud, and parked by the interstate, it was still hard to pinpoint with all the other noises. It actually sounded like it was coming from whichever side I was standing on at the time. I had 2 guys with me, and they tried to pinpoint as well. At least I had witnesses……..that I wasn’t just hearing things. lol
So am I thinking right that, if it’s a valve, it’s probably the kind with an exhaust port that may have leaked at the wrong time? Otherwize, I’m thinking that fittings or hoses would leak and continue to leak?
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Hi Jerry,
You might consider going on the Prevost website and downloading the air diagram for you coach. You will be able to see on the schematic possible sources for a leak in that area. Of course that’s just for the Prevost side. Maybe the converter can provide one for the house side as well. I’m pretty lucky (I think) my converter did not add any house “air” accessories!
I keep my schematic laminated in the coach for quick reference.
Good luck.
Dan
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Jerry, In case this ever happens again get a cheap stethoscope, such as one Craftsman sells. I think they are close to $5. Air leaks that make a lot of noise elude detection because the sound seems to come from everywhere and bounce all over the place.
But with the stethoscope using the funnel end I have been able to aim it at the source. Sometimes simple is best and this is one cheap tool, simple to use, and effective.
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Will do, good Idea
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