Help with Air Compressor on CAT C15

I have a Bendix air dryer I changed the compressor and it still did the same it has to be the dryer

 

What PSI are your tanks at? That safety valve should only pop off at about 150 PSI.

 

My safety valve started popping off last week. My mechanic checked a few things out and was going to replace the valve first before doing the unloader valve. I was on my way to the dealer to pick up the safety valve with the truck and lo and behold my 6 month old AD9 air dryer started dumping air continuously from the purge valve. Bypassed the dryer and everything is working perfectly now. Now its a fight to get a new dryer plus labour. Looks like its blowing the o-ring off the purge valve piston.

 

It is the same problem I had with my AD-9 dryer... It had a bad check valve at the bottom of the dryer... When the check valve gets stuck there is no air flow to the air dryer.... A high air pressure is only in a line from a compressor to the air dryer.. That's why a safety valve pops up all the time.