Small but steady air leak

[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.