[Archived]

If it’s the dryer purge valve stuck you would surely hear the leak. If not at the dryer you have a huge leak.

[Dan]

It is also possible the air source for the accessory pressure gauge is leaking.

[Thomson]

Do you have an update on this?

[Archived]

You could have a leak anywhere in the main air system. I had a similar issue and Prevost found a break line that was rubbing against a chassis part and wore a hole in the line. I saw the exact same symptom that you are seeing.

[steve]

No change on the accessory air gauge when compressor stops. The coach suddenly developed a serious lean in the curb rear about the same time. Ride height to stops in 20 min after key off. Replaced 3 right rear air bags, Norgren 5 port & 3 port above the tag & all new DOT compression brass. The coach is staying near upright after 12 days. 1 problem solved but not the acc air gauge. Still see a 15-20 psi drop when the dryer sneezes. I need to watch the primary & secondary gauges closer to determine if they are acting the same as they would be 1st in line after the compressor & dryer. Got distracted from the coach for a while.

Have not found a leak in the acc gauge tiny air line connected to the converter air manifold. Don’t hear the dryer exhaust port leaking after spitting. Went poking around with an ultrasonic leak detector & could not find other obvious leaks.

Thanks

Roger

[John]

I watched all 3 air gauges while the engine compressor was increasing pressure. Primary, secondary and accessory gauges. When the compressor stopped & fired the air dryer only the accessory gauge took a rapid drop in pressure from 125 psi down to 105 psi and holds at 105 psi. The other 2 gauges only flinched a couple psi & held very near 125 psi. Almost like there is a leak in the accessory system above 105 psi?

[Dorel]

Hi Roger! I’ve been dealing with my dryer also, do you have a good air schematics to look at? I was looking at it thinking about what your saying, I just replaced my 2 check valves at the primary & secondary tanks that come from wet tank, they hold air in Primary & Secondary tanks for the brakes, but if you look from the wet tank the 2 lines that leave the wet tank, 1st one goes to Primary in rear(only) then the 2nd line from wet tank goes to secondary tank, but it also goes to supply acc tank with air, it goes thru protection valve at acc tank which is open till it hits 75 psi. So if the dryer is sneezing way to much air the Primary & Secondary tanks have 1 way check valves to hold air in, but acc tank does not, but maybe the protection valve at the acc tank is bad? So if the wet tank looses air quickly it will affect the acc tank, and if the check valves are holding the Primary & Secondary tanks won’t drop. I was reading about dryers, and they talk about a small amount of air drop when it sneezes ? Maybe dryer is sneezing way to hard and the acc tank isn’t that big. Maybe Dryer has a problem. I would like to up grade mine from Wabco Saver 1000 to the saver 1200.

[Jimmy]

Is it possible that your aux compressor is set to 105 psi and the regulator is bleeding off the excess? My aux compressor has a check valve to hold system pressure and not allow bleed back to the compressor. If the check valve fails then system pressure could be dropping to the aux compressor setting.

Doug

[Dan]

Hi Art, thank you for all the detailed info. The 1200 dryer sounds normal with a 10-20 sec purge. I assumed the acc tank filled from the secondary tank. The pressure regulator to the acc tank holds air back until 70-75 psi. But on a previous coach that same pressure regulator filled at 75 psi but also started leaking above 75 psi. Definitely requires a closer look. The air dyer note regarding a normal 10 psi drop in 1 of the gauges is interesting. Maybe that is a normal response for the acc tank gauge. Again the acc tank regulator requires a closer look. Possibly a purge valve rebuild is in order.

Hi Doug, thanks for your experience with the check valve. I recently changed the check valve & decompression auto drain valve to solve a different issue of the aux compressor not restarting under head pressure load. At that time i checked the diaphragm of well pump pressure switch. It does not leak. Also no longer leaks back to the aux compressor.

Thanks again for all the great feedback. I have a couple more items to check into or live with it.

Roger

[Robert]

Roger send me your e-mail address and I will send you a copy of schematic Art art.twaddell@gmail.com e-mail me.

[Roscoeapproved]

Roger,

I sent you an email a few minutes ago.

Ron

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Jeff and Lindsay

91 Marathon XL

[Dave]

Just commenting on what I think I understand and that is accessory pressure can leak back through the aux compressor, but that is why Liberty has a solenoid valve (and maybe a check valve) in the line from the aux compressor to the Liberty manifold.

[Art]

Hey Jon, the Liberty installed Versa valve & Watts auto drain filter are what was replaced. This solved a problem with the aux compressor not restarting with head pressure. Eventually i will install a large capacity filter.

The initial pressure drop following the dryer purge is a result of the SS1200 air dryer. It uses air from the wet tank for the purge. This was clarified by Art’s documents.

[Roger]

Just finished the dryer up grade as per Prevost new brake relays valves-all rubber brake lines, started up dryer purged at 120 psi much stronger purge and cuts rite off after purge. So I read this dryer has air inside of its self to purge way larger unit had to weld an extension on bracket and extend supply side of dryer.

[Archived]

Nice having an air dyer that stores it own purge air. Harder to service the AD-9 cartridge but you will like the performance.