[77newell]

Now that I've eliminated the leak in the step slide I'm down to the air compressor running about once per 20 hours more or less. Now I have an interesting leak down situation. All three needles (2 brake and 1 supply) drop in unison. So, either there remains a leak in the systems from the supply tank and bot check valves on the two brake tanks are back flowing at the identical rate, or there are equal leaks in each of the two brake systems, or there is some common place where the two brake systems somehow come together and a single leak could effect all the pressures equally. None of these three explanations seems plausible. It's a puzzle that I'll be noodling on for a while it seems.Given the leakage rate it's not like this is an urgent problem. Actually, if it was just the leakage rate I wouldn't be bothered. What bothers me is I can't figure out how the leakage pattern is possible. I hate being stumped, it's one of my several mental obsessions.

Any thoughts?

[HoosierDaddy]

Jon, My compressor runs once/hour........You are invited to come and chase leaks here...Maybe that refocus will help!!! ;-)
Seriously , could the leak be in the compressor?

[ccjohnson]

Leaking at the gauges?

[77newell]

To answer the last two questions asked;
I doubt it's the compressor for the following reason; there is a separate check valve at the inlet of each brake tank. In order for a compressor leak to be the problem both of those check valves would have to be leaking and at the same rate since the needles are dropping in tandem. My 120V compressor feeds into the inlet of the main air dyer.

The gauge with the twin needles for the brakes could be leaking internally. I did have a small leak in one of the two fittings on the gauge and they now check leak free. The reason I doubt the leak is internal is that I would not expect a single internal leak to effect both needles. If there were to be two leaks internally the odds that they were exactly the same size strikes me as nearly nonexistent. However, I am assuming that the internals for the two needles are independent of each other. I may lack the imagination as to a configuration where they aren't independent.

There is a place where the two brake circuits come together, the parking brake knob device. OK, it has some other fancy name that escapes me at the moment. While only the rear brakes have spring-brake actuators on the (I believe), both brake tanks supply pressure to the knob device. I've examined a cut-away of that device and failed to understand exactly how the two supplies are used. Today I will leak check that. At 50-60 psi the leak down is only 5 psi per day so the leaks I'm trying to find are tiny, but to salve my obsession, I hope are detectable. I will boost the pressure to the cutoff of the 120V pump.

I appreciate the suggestions, as I consider them they deepen my thoughts and understanding even if I conclude they aren't the solution in this case. Any time I can better understand this complex air system I know it will be useful in the future. For those of us to whom complexity is scary, your gifts of suggestions are invaluable.

[Richard]

And the two brake tanks come together kind of at the brake treadle. You may be on to something, it has to be downstream of the brake tank PPVs and common to primary and secondary systems.

If the brake tanks leak down the supply side will try to replenish them and thus be at the same pressure.

I find some air brake schematics that show a double check valve that combines air from either tank and sends one line to the E brake release button. I don't know if we have that setup or not, but it's something to research,

[77newell]

You conclusions about the relationship of the service tank and the brake tanks is consistent with my own understanding which is why I have been focused on the brake system which in theory has each system sealed from the other and at least from what I find from vendor literature they indeed are separated by either separate tubing or o'ring seals in the common devices such as the brake treadle and the e-brake/parking brake valve. The brake system should, and does leak down very slowly and I'm wondering if that is just the way they are given all the parts and pieces involved. Still, my engineering mind wants it perfect. I suspect this leakage has probably existed since I've owned the coach and only became apparent now because of my diligence in eliminating the non-brake systems leaks. If so, I should interpret this as a sign of great success instead of kvetching about it.

[folivier]

Yes Jon it was like that when I owned it. Perhaps my not being trained as an engineer it didn't bother me as much?
Hey, the brakes worked when they should so that was my only concern!
But congrats on getting the air loss down so low you should be proud as any Newell owner would be.

[77newell]

Thank you Forest, coming from you that is a real compliment.

Perhaps it's less about my engineering training, which was minimal, than it is a genetic disease. I can't complain too much, it generally serves me pretty well, mostly usually