[Wanderman]

Steve and I have been on leak finding patrol today and found something odd. When at 110psi on shop air we hear leaks in the lines coming out of the engine mounted air compressor. If the pressure gets below around 80psi it seems to stop.

Is there some kind of valve or other mechanism inside or inline that would cause this?

Sounds like a lower pitched air leak.. Almost a moan. You can here it flowing through all lines exiting the compressor.

Thanks!

[Jack Houpe]

Rick being a compressor I would bet reed valve but don't hold me to it as I have never had one apart. The moan you are hearing might be from one of those valves leaking by but I would think there would be a check valve in there someplace. You can hear this with your ears?

[Richard]

It could be the blow off valve on the air drier is leaking. It opens and closes based upon the pressure in the system. The engine compressor runs ALL the time being gear driven. The blow off valve opens and closes to allow the compressor to either freewheel OR provide compressed air into the system.

If that valve were leaking it would allow air to pass backwards into the compressor.

You can buy a rebuild kit, but most people find it just as economical to replace the unit.

It is likely a Bendix AD 9 or AD 7.

Word of caution, do not futz with that valve in the middle of your trip unless you have the parts to replace it. IF it fails to reseat, you will not be going anywhere until you get a new one.

[Wanderman]

Richard,
I understand the engine driven compressor philosophy you've explained.
Maybe.
If I am NOT using the engine to drive the compressor. Either using the 120V or shop air and we hear the air in the lines feeding the compressor, would that be the valve in the air dryer or something in the compressor itself? (unloader???)

This is mostly new to me and I'd like to learn for future failures.

We're at Steve Magown's and both of us are scratching our heads after being under the coach for a day tracking leaks.

Thanks!

[[email protected]]

I am having the same issue with mine, I can hear air flowing through the intake hose of the engine driven air compressor. This should be stopped at the air dryer as it has a check valve of sorts that keeps the air from flowing back to the compressor. I believe that Richard is correct, this is a part of the purge valve on your air dryer, you can either rebuild the purge valve or replace the entire unit. I have a newer Wabco 1200 air dryer but my coach is a bit newer. I have a new purge valve to put in mine to see if it cures the issue but have just not gotten to replacing it yet.

[Jack Houpe]

AHAA, I did replace my air dryer soon after we bought the coach, makes sense about the air dryer allowing reverse flow back through the compressor. One thing nice is they are cheap but its a nasty job.

[Wanderman]

So after a visit from a great diesel mechanic with amazingly sensitive ears! We discovered the main source of the leak, at least on the white needle of the dual needle brake gauge.

Under the dash is the primary brake manifold (your pedal attaches to it) and among several air lines there are some larger ones that come up from the primary and secondary air tanks. One was leaking very badly. But since the air was traveling down the hose, it wasn't making enough noise to be heard. We got new ends (swivel 90 degrees) and replaced the bad one.

Now I have the White needle essentially static when no air is being fed to it. However the Red one and the Supply one are still dropping rapidly. 90 to 70psi in about 20 minutes.

We only had one of the swivel 90's to use, as I had no idea those sizes were there. I will be buying several more and replacing the other one and perhaps some of the smaller ones I havent done yet.

Maybe that will stop the leak on the Red and supply side.

Steve Magown is/was/and will be a tremendous help and a Gentlemen!

The assist, phone a friend award goes to Richard and Jack, who were extremely helpful. Jack even fired up his coach and did leak down timing tests with texted photos. We were able to use that as a baseline. Invaluable.

Not perfect, but far better than when we began

[Jack Houpe]

Glad your getting it sorted out and found someone with good enough ears to pick it up, glad to help.

[[email protected]]

Guess I should have posted it, but I also had the same leak at the fittings going into my brake treadle. I was camping at the Wanderlodge rally and that is when I heard the leak under the dash. I just pushed the tube into the fitting and it quit leaking. I want to get back in there and move the air lines, they have them bent in such a way that it puts stress on the fitting, I think it would be much better if the tube were going straight into the fitting.