On our last trip we were on the side of the road due to losing air pressure. It turns out it was the air dryer purge valve. I have always called this purge valve a pop off valve. Well, that terminology got me into trouble. Foreforum members have posted a lot about servicing the air dryer. So, every 18 months I have FOT service the dryer. The repair order says that they replace the air dryer filter and the popoff valve. The repair order then list a air dryer mod kit and a 200 pressure relief valve. I telephoned FOT and was told by the service writer that the pressure relief valve is the popoff valve. And, was also told the purge valve (what I call a pop off valve) is not a maintenance schedule item and is never replaced unless there is something wrong with it. In other words, unless it fails to release air pressure at the 120 or 130 psi level in the shop when the air dryer is serviced, it is considered ok. Unless there is specific request to replace the purge valve, it is never replaced. I am beginning to wonder how long I will have to own this motorhome before I can ask to have it properly serviced.
Larry
This is why I prefer swapping out the old dryer for a complete rebuilt unit. You get all the good stuff in one package. Except for the "isolation valve", which is required on my AD-9, and not included with a rebuilt dryer. May not be required on all dryers...
You can find the isolation valve on line for 20 to 30 bucks.