Bendix AD-IP Air Dryer question..

Well the main trouble turned out to be the AD-SP air dryer as suspected.
The check valve leaking was just another kinda unrelated item.

I opted for HALDEX this time, since its not a re-branded-bendix same thing.
This was the 3rd Bendix AD-SP I have had issues with.

The HALDEX unit is a bit more compact and has a few extra features I like.
Hard to find one of these though. I had to have it drop shipped from HALDEX directly.

Now, when the dryer sneezes at 125PSI..the tank pressure only drops to about 122PSI and will hang there.
No more cycling or sneezing every 30 dam seconds.

I did discover a slight air leak on the #4 dryer input line (unloader line to governor) and I will have to get a new fitting
on that this week. It's not bad but did show bubbles when I was testing all my fittings.

Fix one problem...discover another...

 

You should have considered upgrading to AD-9 unit. AD-SP didn't do good job of drying air despite of couple rebuilt kits thrown in it. I replaced it with AD-9 and no issues so far

 

If your system purges constantly there are only a couple possible causes
Purge valve In the dryer leaking, line from the dryer to the governor leaking, valves in the compressor leaking , and I'm guessing by the higher rpm that the valves in the compressor is you problem

 

I got an unloader valve rebuild kit ($12) but since the issue stopped once I replaced the dryer - I am not going to replace those yet.
Besides, it looks to me that the intake manifold will be in the way since it goes virtually right over the top of the compressor.
I only have a few inches in there to even work with..