Air tanks no air

Drained water out of tanks through purge valve?

Last time changing out air dryer?

 

@nasriza @DUNE-T may have some ideas

 

Should be 3 tanks on the side of your truck, which one are you referring to?

 

That tank stores moisture and is only pressurized when the compressor is running. The 2 other air cans are your primary and secondary. Nothing to worry about

 

Wait what?!? How does that work? The tank gets pressurized from compressor and then that air pressure goes to the other tanks and that tank is then empty till compressor kicks on again? How does it empty to a higher pressure tank?

 

There is really 4 tanks in Volvo first tankbyour wet tank is split in 2 there is a valve inside that fills up tank at pressure governor cuts off so it can keep the air dryer from chuffing excessively it only gets air right about time air compressor shuts off. Behind is the wet tank than primary and sevondary tanks

 

Any idea what's going on here? It's on my 2000 Volvo with Detroit. Every 3 minutes or so, the front tank pressure starts going up, then it purges and then repeats, while the 2nd tank just stays at 120 the whole time.
Can't find any leaks and already changed air dryer with filter, rebuilt fan clutch, put new governor and checked the compressor, everything seems to be fine
https://youtube.com/shorts/tU9oD2CyX_o?feature=share