Supply air system

[revlimited]

Hi truck is a 2007 freightliner Columbia. Has an air dryer connected to the primary tank. Almost like an AD-IS. When both primary and secondary tanks reach 135 psi, the purge does not burst air but slowly leaks out air for 20 seconds. While this is happening both tanks drop to 125 and it starts building again back to 135. I have replaced the white check valve, spring and o rings with bendix kit 5004052. The check valve which I removed was broken.

So whats the problem? Why is the truck losing primary and secondary air when its purging?

[Nilao]

Could be the body itself is worn out...they do have a service life expectancy...i think i would just swap out the whole assembly and be done. It might be cheaper than throwing parts at it hoping to figure it out.

[imalumberjack]

I had the same issue ...... I tore the whole effing thing a part!!!!!!! governor .....tried to get into side valves .......I was not happy.
So my fix was replacing the purge valve ....its been awhile but it seemed there was special instructions? also there is a tiny line that went from air compressor to valve make sure its not clogged with soot?

[kmk]

Check your governor and the purge port. That white check valve supplies pressure to the governor, in turn it unloads the compressor and the purge valve. Sounds like restriction.

[revlimited]

So no chance it has anything to do with unloader valves in compressor?

[kmk]

The port on the back of the governor sends signal to the purge valve, either governor or restriction to the purge valve.