purge valve won't shut after purging

This has drove me insane for the last 2 weeks.

After reaching 130 psi, purge valve purges and everythingis okay until the compressor kicks in again at 100psi.

I can feel air coming out the bottom of the purge valve horn. If I keep my finger over the exhaust port on it for about 3 seconds, it closes and the system builds up to 130 again no problems. The cycle repeats itself again at 100 psi. Once in a while it'll work correctly for a few cycles.

Just had new AD-IS dryer replaced. 2 purge valves replaced. Governor about 2 years old and air comes out of small line from it when system purges.

Seems like something is keeping the valve open when compressor goes to BUILD AIR cycle. please help. 2003 Detroit 60 DDEC4

 

Took out the unloader valve and the housing it sits in. Applied some white lithium grease to all the o-rings as well as the little plunger and put it back in.

Then took out the purge valve from dryer, also applied liberal amounts of white lithium grease to all the orings and put the valve back in.

Also gave the dryer mounted governor a couple of really good whacks.

Drove home (about 450 miles) problem seems to be solved. My bet is the purge valve had to be greased up but it's hard to tell what exactly solved the problem

 

Quick update.

After about 500 miles, the problem returned. Made it to local Freightliner stealership and bought a THIRD purge valve kit in about a year. Installed it. Truck has been running and purging great ever since then. (600 miles so far).