Air-dryer leaking

I’m sure that’s the way air system are supposed to act. It may be that you’ve had a probalem since you acquired this truck. Now you have another issue that’s causing it to be unacceptable to drive.
The tank that drops to 90 has the issue. It is leaking air, sounds like a bad one that won’t pass a DOT inspection. It could be that both the check valve at the air drier/wet tank and the wet tank to primary or secondary whichever is leaking. Which could be leaking that 30 psi back through the air drier.

If you idle your truck until both tanks have 125 and as soon as the air drier purges, shut it off. Listen for where the air is escaping. If it’s the air drier you’ve got check valve issues. More than likely your going to find a line, air bag, or something else hissing air out.

 

So when the purge valve opens, unloads the drier and the compressor is not pumping, the purge valve is open and stays open until the governor reactivates it at the same time as the compressor kicks back in. If the drier is still allowing air out it’s because either the air compressor is still pumping ( air will pulse as it comes out, and will not leak when shutting down after a drier purge) or the check valves between the drier and all air tanks. (Will be a steady release after a purge).

 

Pipe Thread sealant. Not tape. I prefer the Permatex with teflon. Keep the teflon tape in the @ home toolbox.

 

kinda funny i just posted a video today on changing a ad-9 air dryer

iv been using loctite thread sealant 567 thread sealant on any pipe thread fittings for a little while and been having great luck with it.

 

I’ve fixed so many of these pull the snap ring out in there and the purge valve will drop right out/might require a little yank if it’s dirty, 99.9% of the time it’s the o-rings. Pull it out and if the O-rings are in fairly okayish shape slap some grease on them and slap it back in. Worst case scenario new o-rings, and btw you don’t need to take out those bolts you mentioned