Secondary air tank filling, primary not filling, valve problem?

what valve controls the handoff between primary and secondary tanks? my understanding is the compressor goes to air dryer, air dryer goes to wet tank, then wet tank fills primary/secondary.

usually this truck fills primary first to 60, secondary starts to fill until they are both at 60, then they both climb to governor shut off at 130ish.

been sitting for a week, now secondary fills to 60, pauses for a few seconds, then secondary keeps filling to governor shut off at 130ish, primary dead empty.

what valve does the handoff between filling one or the other? attached some pics of the tank connections.

on this truck the "wet" tank looks like one long tube with the air dryer at the back, i guess it's the wet tank and secondary tank in one unit? the front drain on secondary (below all the connections) has air, the back drain only has air in it while compressor is running, as soon as governor shuts off and the dryer purges the rear drain has no pressure. the "primary tank" is two tanks at the front with green lines, one green line connects them, and one black line with a check valve.

all drains are bone dry, have been for seven years, never had water come out of them, desicant gets swapped at least twice a year, purge valve not leaking. just not air getting to primarys

 

no. air only comes out of purge valve when it purges, no leaks after that. primary doesn't have pressure in it at any time.

where is the dryer output check valve, is it built into the dryer, inside the housing?

on this truck the dryer just has input (insulated), grey governor hose, and green output.

that's why I'm trying to figure out what valve does the balancing between tanks and where it is, where it splits after the dryer. compressor good, governor good, dryer good... either primary input check valve stuck, or splitter valve stuck.

 

2017 cascadia but the old style

 

it's not the gauge there's just a little whisper of air from the primary drains

 

secondary tank fills directly from the air dryer, there's a hole on the back of the dryer that just butts up against the tank with an o ring, air goes straight thru into tank, the green output line coming off the dryer below the governor is just for primary tank. that means dryer or governor problem because secondary is filling but primary not filing. don't see how it's the governor tho if secondary fills to cutoff and governor pops off like normal. guess that leaves *air dryer clogged with something*. ??


fitting hasn't seen the light of day since the factory 2017 lol



cloth air line from compressor



not much left