Small but steady air leak

[johnklopp]

One engineers approach, Make the leak larger and easier to find by reducing molecule size.

If the leak is almost impossible to find, consider putting helium into the air system rather than air. The helium won’t hurt anything on the suspension; but will leak more than 10 times faster for the same size hole and pressure. Helium is readily available at most party stores for inflating children’s balloons. The reason is simply the molecule size. A helium balloon shrinks because the gas molecules within the balloon can slowly pass directly through the permeable rubber of the balloon, air does not. Tires also have a permeability ratio that will allow them to very slowly deflate. A helium molecule may be the smallest molecule in existence. A carbon dioxide molecule (Air) is much larger, composed of one carbon atom and two oxygen atoms.

Remove the helium before driving the bus.

[hobobimmer]

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

[dogear]

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

[ajducote]

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.

[Jon Wehrenberg]

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.

[Charles Spera]

Hector/Jon,
My coach is not leak free but with all your help I have chased down a lot of them and have only one interesting situation to share.

Occasionally (not always), when I return to home base and lower the coach all the way I will, after a short while (couple of hours), start to listen to the aux pump cycle every hour or so. Sometimes I ignore it and it seems to cure itself in about 8 hours or so. On the other hand, Ms Barbie isn't always so patient with it. Fiddling around I have found that if I cycle the Level Low switches a couple of times with the ignition on, it will cure up immediately.
My conclusion is that I have a shuttle that doesn't always seat correctly. Since I can work around it I have decided not to go on a full bore leak and valve replacement safari for now.
See you in Austin.

[LNDYCHT]

Andre,
I would bet that when you take your coach of the stands you will find that your air leak will be there once again.

[Jon Wehrenberg]

Lee,

One thing we have learned is we have to think of air leaks in one of three ways. Brake system, aux air system, and suspension, which is actually three systems, front, left and right. A leak in the suspension will not necessarily pull down the pressure in the aux system, and conversely a leak in the aux system can go to zero and not cause the bus to lean or settle. Or the reverse could be true which is why leaks are such a big PITA.

[LNDYCHT]

The only point that I was trying to get across in my last post is the fact that system pressures and dynamics change when the weight of the coach is removed from the suspension.....

food for thought or not

[Jon Wehrenberg]

Can you elaborate? Are you suggesting supporting the chassis (or removing the chassis support) will reveal or mask system leaks?

If everything is leak free (there's a pipe dream) we have primary and secondary brake systems, auxiliary air system, and (3) suspension systems(s). I can't think of how supporting or removing chassis support will reveal or mask any leaks.