[Brad Townsend]

So I am back to chasing down my air leak and was under the coach looking for a drain on the wet tank and found it had an automatic drain. I pushed on the what looks like a stem valve to make sure it worked and it did no water came out only air.

I also noticed a horizontal tank not sure what it is, it looks to be about 4 inches in diameter and 14 inches long with a breather cap on top and a drain petcock on the bottom. I opened the drain petcock and nothing came out. Does anyone know what this tank is?. 

The 2 air tanks up front I opened the drains, the forward tank was dry and the other one had about 1/4 cup of water with a small bit of what looked like oil.

So on our way to our winter location we lost a brake diaphragm and had the whole chamber replaced.
I am wondering if there could be another diaphragm with a leak but can't detect it because it is inside the chamber housing. 

Yesterday I ran the engine and filled the tanks and now this am the supply is empty and the brakes have about 15 lbs.

I am planning to replace my old air dryer at some point this winter.

[Keith Jordan]

check dot valves between brakes and supply tank.Mine did the same as yours.front dot was bad.changed it and brake tank holds for two weeks now.then I could look for leaks on supply side only.cuts down on looking for leaks in the brake system

[Brad Townsend]

Don't know anything about those valves. What do they look like and where do I get replacements?
Would they show a leak with soapy water?
Is there a way to prove they are bad?

[Fulltiming]

They are located on the air brake tanks themselves. They are check valves to prevent air from leaking out of the tank back into the supply system. Although it is possible that they are leaking where it is visible, they can have debris or rust preventing them from properly sealing and allowing the tanks to bleed air back into the supply system. If they have not been changed out in a significant period of time, it is a good idea to change them IF you watch your gauges and see one or both brake tank pressure gauges dropping at about the same rate as the supply tank.

Bendix 800372 SC-3 on my coach.

[encantotom]

that tank with the pitcock on the bottom and cap on top sounds like the slobber tank for the engine to me. usually it will be full of dirty oil.

tom

[Brad Townsend]

Thanks Mike and Tom
Mike that sure sounds like it could be the problem.
How many valves might I be looking at? I have had issues with other smaller check valves. As far as I know they have never been changed.

[Fulltiming]

There is a check valve on each of the two brake tanks on the inlet line.

[Brad Townsend]

            Are the air brake tanks the square tanks welded as part of the frame. I see large lines coming from them to the air bags.

[Keith Jordan]

Are the air brake tanks the square tanks welded as part of the frame. I see large lines coming from them to the air bags.

those are for the air bags.brake tanks are round.

[Brad Townsend]

So I have what I thought was a wet tank in the rear which is round and 2 round tanks up front.