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Trying to trace Air System lines on SMC-Beaver Magnum chassis


CountryB
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I'm losing air in both tanks rather quickly (over night or faster). I have not found any major leaks yet (I did find a good leak at the pressure relief valve on the  air tank and plugged that) .

However I think the Primary and Secondary air systems are not staying "separated". I'm trying to figure out where the two air systems (primary/green and secondary/red) tie together. Usually trucks will use a "shuttle valve" to connect the two air systems together - so if one side loses pressure the shuttle valve will slide over and  block that port and continue to supplying air pressure (to whatever component) from the air side that has more pressure.

I'm losing air in both sides equally fast. so I think there is a "shuttle valve" somewhere that is not closing. I cant think of anything else that would let both tanks drain equally.

An Air System schematic would be useful - but there dotn seem to be any for the SMC Magnum D-series (Blue Diamond) chassis.


I have three air tanks. There are two stacked tanks on the outside of frame near front of coach, and one tank in the rear over the drive line.

The rear tank only has two lines (and a tanks drain line). One of those lines goes to the Relay Valve for the  Tag Axle brakes. The other (black) line is the supply from the front tank. Also the Red line on the bottom tank (the one wire tied to Black line) looks to be feeding the rear Relay Brake valve for the Drive Axle.

So the problem must be in the front of coach somewhere. I need to trace out the Red and Green 5/8" lines that go from stacked tanks toward the front.

Does anyone have any ideas or other places to check?

Beaver Air Tank line routing.jpg

I have not  located the air supply line coming form the Air Dryer. It's a 5/8" Green line. That could be the green line that goes into the lower tank (at the right just out of the photo). That green line goes into a pressure protection valve at the tank.

I need to trace those two 5/8" lines going toward the front of coach.

 

 

Edited by CountryB
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Mike,

I have developed a similar leak on our coach where both the tanks leak down in about 24 hours. Have not looked into this yet but I remember Van Williams chasing an air leak for days before finding it to be the treadle valve up front. I plan to look there first. If you have not checked the treadle valve you might want to give it a look.

Edited by Bob Nodine
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Just thought I'd add - both of those "stacked air tanks" (in my photo) have "internal check valves" that separate the Wet and Dry sides of the tank. I'm going to try to remove one ans see if it can be cleaned (I doubt there is a replacement available).

 

 

Air Tank - Internal Check Valve.jpg

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That sounds like a quite extreme measure, do you suspect that the air dryer did not do its job? I never got any water from the wet tank when drained. Even if one of the check valves was stuck partially open, could it cause both leak downs? Getting both stuck at the same time sounds weird, especially in the top tank's wet side that could be probably considered a 'second stage' wet tank. I think, if I wanted to verify the check valves, I would just use a gauge on the dry halves and regulated pressure drop on the wet side port and then maybe the other way around.  

If the break pedal did not have a leak, there are still quite a few smaller lines up front to the gauge, park break, step slider, horn, vacuum gen and who knows what else you might have there. Some of them should not leak below ~60psi. I know you know that.

Personally, I would not even worry about an overnight leak down, as long as my air leveling holds pressure. But I get it, if you want to make it perfect.. BTW, I can't believe how clean your tanks and hoses are after those years.

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12 hours ago, Ivan K said:

That sounds like a quite extreme measure, do you suspect that the air dryer did not do its job? I never got any water from the wet tank when drained. Even if one of the check valves was stuck partially open, could it cause both leak downs?

Getting both stuck at the same time sounds weird, especially in the top tank's wet side that could be probably considered a 'second stage' wet tank. I think, if I wanted to verify the check valves, I would just use a gauge on the dry halves and regulated pressure drop on the wet side port and then maybe the other way around.  

That's a good point. 

I know there is some internal leakage with the check valves because I can air up the tanks and then drain the Dry side tank and pull off the feed hose and I will get some small air flow out of the Wet tank. So the check valve is "seeping" but that is an internal leak, and I need to focus on finding the external leaks.

I can look in the end of the tank (plug removed) and see the check valve. It looks pretty clean, but I cant see the sealing seat of course.

Regarding soapy water - i am spraying everything. That's how I found the leakign "safety Relief" valve I asked about in my first post.

I also see two other small leaks. On is at a brake valve "fitting", the other is on the Tag Axle dump solenoid. I don't think it is worth messing with the solenoid, and the fitting is hard to get to. They look to be small leaks so I 'm not sure it worth messing with. But I suppose all the small leaks add up.

Today I plan to spry the air system at the front of coach (there's not much up front, except the treadle valve). I did spray the HWH 6-pack and did not see any leaks there.

Air leaks at brake relay vale and Tag axle valves.JPG

Edited by CountryB
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