Small but steady air leak

[Kuhlsport]

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.

[Jon Wehrenberg]

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.

[ajducote]

An update. Thanks for all the input, it all helps.

I have been studying the Prevost diagram and have started a very slow and methodical check of my air system. The leak is so small, I not sure I will find it, but I want to try.

I started back at the air compressor, spraying soapy water and checking for loose fittings. So far no bubbles, but I found 1 small fitting on the "unloader" on the back of the air compressor that was just a 1/8 turn loose. Also the 2 bolts that hold the "unloader" on the compressor where just a tiny bit loose. So I tightened them up. It does not appear that is where the leak is. SO next stop is the wet tank fittings and all the fittings on the air dryer.

I have the bus up on Jon's stands and I am able to safely crawl under the bus and check 1 or 2 parts at a time. Since I have found a few very slightly loose fittings, I guess I will put a wrench on every fitting I can find and see if I stumble onto the leak.

Just to be clear, it is a VERY small, Very slow leak. I could ignore it for now and wait to it gets a little bigger and it might be easier to find. BUT, until a week ago the air system on this bus has been as tight and leak free as they come. It was so good for so long, I really want to get it back to air tight if possible.

[truk4u]

Andre,

I can send you my electronic stethoscope if you want.

[ajducote]

Tom,

Thanks for the offer, that would be a big help. Will send my address in email.

Thanks

[LNDYCHT]

In my experience chasing leaks it is seldom fittings and usually devices such as valves. Both of my coaches had leaks at the belt tensioner control valve when I purchased them. The new coach also had a leak at tag axle valve, this leak was very small and not always present.
I found the best method was a stethoscope which is easily obtained at a tool store, I extended the hose on mine with a piece of tube and removed the amplifier device from the end so that it is strictly hose. You definitely know when you are close to a 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.