Air pressure trouble

[mlh2013]

I have been trying to help my brother with his 98 diplomat. His air pressure pops off at 120 psi just like it should but want stop until it drops to 90 psi.then dryer closes off,compressor kicks in and it builds back to 120 and same thing over again. All this takes place over about 5 minutes or so give or take. Checked for air leaks found nothing was told dryer was bad, so we changed it out same thing happening.Then we were told the governor was bad so we changed it out same thing still happening. Has anyone had this problem and can give advise? It is a haldex pure air dryer the compressor is a holset. Thanks

[ecurb74]

When they replaced the dryer did they rebuild or replace the isolation valve? That has been the source of the rapid recycling as you described along with the governor. I'm looking at a dryer replacement or rebuild myself so I've been reading up and came across that yesterday. Maybe this is a start.


Bruce & Teresa
40' 2000 Foretravel U320
Cummins M11 450hp
Allison HD4060R 6 Spd W/Retarder

[ecurb74]

Here is a picIf I can figure it out.


Bruce & Teresa
40' 2000 Foretravel U320
Cummins M11 450hp
Allison HD4060R 6 Spd W/Retarder

[rssnape]

Did you check for air leaks with the engine off? 30 lbs over 5 mins might be difficult to hear.


1997 Tiffen Allegro Bus 37', Cat 3126

[mlh2013]

No Bruce we didn't change the valve you described. Where is it located? Is it on the air compressor?

[mlh2013]

Yes we did check for air leaks with engine off.

[twinboat]

Yes I have had this problem many time in my career, working on heavy equipment.

Check the small line from the governor to the air dryer. If it has a leak or loose fitting it will do just what yours is doing.

One other thing to check is the check valve, on the wet tank. Follow the air dryer line to the first tank. The check valve should be on that fitting. Take it off and take it apart to see if it's stuck.

[3rd stage]

I think the valve in question is called a purge valve. It's generally built into the holder for the air dryer canister. They get old and leak. Just had a rebuild kit put in mine because of leakage after shut-down.
Andy

[mlh2013]

Took the new air dryer back to napa and they are sending it back and going to get another one. We were told that one is bad. It will be Monday before napa gets it in not a stocked item.