Losing air from primary tank to air dryer (long)

Hello,

I have a 2004 Freighliner with a Pure Air Plus dryer that has been purging air every 30 seconds or so.

I have installed upper and lower kits on the dryer, changed the governor, and installed an unloader kit at the compressor.

I put an air gauge on the primary tank on the automatic purge valve just under the primary air tank' s inlet hose from the dryer and observed the pressure build to 135 and then the dryer's purge valve dumps and the gauge drops to 120 on the gauge, holds there for about 5 to 10 seconds and then climbs to 135. The cycle continues after this. The pressure holds constant at 135 down stream of the inlet valve on the primary from the dryer.

Haldex says to check the check valve at the bottom of the dryer. I have put it back together three times. It is a very simple check valve, one disk, small spring and an O ring. They advised to add another one way valve that I haven't done yet.

Freightliner sent a diagram when I called them.

Anyone have ideas?

Thanks!