air dryer constant purge

After reading almost every posting I could find I thought I understood this system. And yet again I'm wrong. The air dryer is connected right to the air tank,and governor to airdryer. Has a smaller twist on filter. The purge valve is constantly exhausting, but like a single cylinder exhaust, its contlstantly "pop pop pop". Not just a steady blow, and only happends onceit reaches 120lbs. The dash gauge does not show it losing any pressure though. I unhooked the air line at the unloader at the compressor and it stops. A short burst of air comes out of the line. Once i plug it bk in, a few seconds later the dryer purges once and right bk to "pop pop pop". My idea is to replace filter, governor and maybe the purge valve. But if this description throws you a dead giveaway, please pipe in! Thanks

 

Well it was something stupid/minor. When I pulled the air gov. Off it has a fittingvwithvan o ring that pushes in to the dryer housing and appears to work a plunger/spring deal. The o ringvon the fitting was stretched out. Put a new o ring and new gov gasket on and reassembled. Problem solved!