Help identifing air system part - 2002 Spartan MM

[dansawyer]

The Chassis is a 2002 Nat'l Tradewinds on a Spartan MM Chassis. I am chasing an air leak on the primary, dry side circuit. Below is a part behind the tanks. The picture is rotated, up is to the right. There is an electrical connection and what looks like a solenoid. Can anyone identify it?

[Lt Dan]

With the electrical connection, my best estimate would be the suspension dump valve.

[dansawyer]

I am chasing a leak.

I found a drawing and was finally able to read the color legend, green is system 1, primary; red is system 2, secondary, and blue is suspension.

The traditional 'wet' or supply tank appears to hold air. The secondary tank holds air. The primary tank is loosing air pressure. There is a PCCV between the supply tank and the primary, it appears to be working.

The two lines above are green, these would be system 1. I would chase 'rear abs valve' and 'quick release valve' as suspects. I have been spraying soapy water but have not tested this area yet.

(I hope it is not the treadle valve - I suspect it is not a reasonable cost item.)

[dansawyer]

Based on the drawing and the comments I went back out and looked for more detail. The two red hoses connect to the tanks. There is a third, not visible blue connection. There is no device in the diagram that matches the part, however the two red and blue connection indicate the part is part of the 'suspension'' system.

I wil keep searching, however for now this is not likely part of the circuit I am interesting in.

[Ray,IN]

You never said, is that part leaking? I have been lucky and solved an internal leak past "O" rings by removing the compressed air In line, adding a few drops of air tool oil and cycling the valve a few times.
DO NOT use motor oil, the additives may damage the O-rings and seals.

[dansawyer]

Originally Posted by Ray,IN

You never said, is that part leaking? I have been lucky and solved an internal leak past "O" rings by removing the compressed air In line, adding a few drops of air tool oil and cycling the valve a few times.
DO NOT use motor oil, the additives may damage the O-rings and seals.

Thanks for the reply. I do not know where the leak is. I have sprayed soapy water and nothing shows up. The primary gauge shows pressure dropping, The seondary gauge shows a steady pressure. I am trying to trace the circuit to eliminate the secondary circuit and the leveling circuits.

[dansawyer]

Update:
Well, I have learned a lot and not yet found the leak yet. What I have learned:
First, the treadle valve does not route service air to the brakes. It instead routes control air to air brake relays. I believe Spartan labels these as Rear Abs Valves. These have control air inputs, service air inputs and service air outputs.

Second, each of these lines have a quick release function. The treadle valve for the control air signal and a quick release valve for the service air.

From a diagnostic perspective since the primary tank leaks down but the secondary holds the leak must be in the rear brake circuit somewhere. Also the leak is independent of the parking brake. I will exclude it for the time being.

Next steps:

Raise the RV for safety reasons.

Charge the air pressure in the system.

Shut off the engine.

Follow the rear brake circuit with a stethoscope listening for the leak.

Unknowns:
I have not positively identified the rear brake relay (abs valve) or the quick release valves. Any help with their location would be appreciated.

[dansawyer]

Update:
I have found the rear valves, see pix below. I tested the circuit for leaks and did not find any.
There are four circuits in the pix. The two left and right, one in the middle, and one at the bottom. The first three are primary circuti and part of the service brake system. I believe the one at the bottom is part of the parking brake system.

[Unplanned Tourist]

Originally Posted by dansawyer

Thanks for the reply. I do not know where the leak is. I have sprayed soapy water and nothing shows up. The primary gauge shows pressure dropping, The seondary gauge shows a steady pressure. I am trying to trace the circuit to eliminate the secondary circuit and the leveling circuits.

Check the line from the air drier to the primary tank. There should be a one way check valve at the tank. It could be letting air back out and exhausting out the bottom of the air drier.

[dansawyer]

Originally Posted by Unplanned Tourist

Check the line from the air drier to the primary tank. There should be a one way check valve at the tank. It could be letting air back out and exhausting out the bottom of the air drier.

Thank you. I had over thought that and moved it to second or third. I will check it. I thought the check valve was located in the dryer? I will check that.

Thanks again.

[rag_ftw]

While you are checking the air dryer check the purge valve for not closing fully. Mine stayed partially open and gave the symptoms you are experiencing.

[dansawyer]

We went back out last evening and checked the dryer. The advice to check that was correct. The lower exhaust port was leaking a steady stream. The volumn was about equal to that from a normal exhale.

I will pull the dryer and rebuild it. I hope the check valve parts are included in a rebuild kit.

Because the primary service tank also leaks down I am concerned the check valve between the wet thank and the primary service tank is also leaking.

Thank you for pointing me to the dryer.

[rag_ftw]

I found a new dryer was not too expensive at a truck parts house. Replaced rather than rebuilt my old one.

[dansawyer]

Hopefully one final question:
Where is the check valve in this system?
I am under the impressoin there is a check valve built into the dryer on the output port. Is that correct?
Is there also another check valve on the tanks that needs checking / replacing? The replacement listings commonly show a PCCV that is also replaced.

Thanks, Dan