Air Dryer?

Over the last week, I have noticed that both air gauges, primary and secondary, are dropping pressure from operating 125 PSI to 10 PSI, within 4 - 6 hours. I lifted the rear of the coach with the air bags and used the excellent 'Jon supplied' jack stands to support the rear of the coach, then crawled under to take a look. I used the venerable soapy water squirt bottle on the valves below the tanks, with no leaks. I doused numerous other fitting looking for leaks, but no joy.

But I kept hearing what sounds like air escaping in 10 second intervals (on of 1/2 second, then off for 10 seconds). I hear a slight leak (sort of like a squirt of air, then quite for 10 seconds. It sounds like the leak in internal, being it sounds like the air in being taken from the tank connected to the air dryer. I did not check to see if air was leaking from the air dryer discharge, but should have.

I wonder if a pressure relief regulator inside the air dryer is leaking? Very strange.

Has any others had symptoms such as these and what was the fix?

Hector

Hector,

I think our coaches use the WABCO air dryer and here is the link to everything you ever wanted to know about the dryer including the schematic and troubleshooting tips.

Hope it helps.

JDUB

http://www.meritorhvs.com/MeritorHVS_Documents/mm34.pdf

Has anybody changed their air dryer filter? Does it really need to be changed? How tough is it to change. If I'm looking the correct piece of equipment under there it seems that there is a plug missing on the underside . I say this because it looks really clean inside this little hole about an inch in diameter on the underside of what I think houses the air dryer filter. Can you tell I'm pretty new at this. I'm trying to change everything that needs it so I cvan start out with everything serviced.

I have no clue what to recommend for a change interval but I have changed mine every two years. The result is no issues with the air system such as high moisture or oil in the system, and the frame of the bus near where the dryer "spits" is dry and free of oil.

As the element is working it gets a coating of oil on the surface of the dessicant. Once the dessicant is oil coated (its normal to get some oil from the compressor) it will no longer function and water and oil get past it and into your air system. Life as a bus owner really sucks if you do not maintain the air system because water and oil start affecting how things work, and especially the valves in the suspension system and all your aux air supply devices. I know of one owner whose suspension failed to be controlled because he experienced hydraulic lock on the valves controlling the suspension. That is extreme, but is an example of the type of stuff that can happen.

Change the dryer element routinely, and drain the air tanks every 5000 miles and you will have no issues with the air system in the bus as a result of water or oil getting in it.

I suspect your air dryer element is a spin on cartridge which is actually easy to change. I use a large strap wrench and with a lot of grunting I can get it loose and off. They seem to stick so it does take some effort, but once it begins moving it goes fairly easy. If it was installed without some lube on the sealing gasket I would assume you will need to eat your Wheaties that morning because I use a lube on the gasket each time I install one and it still taxes my superior muscular strength to the limit.

If you see a coating of oil on the bus frame where it "spits" your element is well beyond the point at which it should have been changed.

Please remember that before changing the air dryer cartridge, first bleed (by pumping the brake pedal repeatedly) the air brake system completely. Yes, there are check valves that are "supposed" to prevent primary and secondary tank air from coming back to the aux system, but NEVER RELY ON SAFETY DEVICES to protect you. Bleed all the air out first. Use extreme caution when dealing with the underside of the coach and air systems, as again, there are valves that should trap suspension air in the air bags, but NEVER RELY ON SAFETY DEVICES to protect you. Block the coach body up first before getting under it.
The fleet standard for air dryer replacement PM interval is generally every 20-30,000 miles, depending on humidity/climate. As Jon indicated, changing this too early is never a bad thing. Water in your air system, once it happens, is MUCH more costly. Since the new year, we have had two late 90's Prevost XL's with bills in the thousands for valve and component replacements, both Prevost and house auxiliary air, resulting from water damage in the air system. Hope this information helps.

Scott13
The hole on the underside of the dyer is probably the exit port for bleed air. If you look at the assembly diagram for your dryer, it might show that this could be a threaded port for a nipple.

I've changed mine, and it is not all that difficult. There are several different configurations, so each one has a different procedure for changing. Unfortunately, mine is located in an awkard place, but it is a spin-on. Like Jon said, without change intervals, it is hard to know for sure, but I too have changed mine every 2 years on both buses I've owned.

Pictures of the dryer base.

Sorry if this is annoying, I have to keep in practice posting photos as it is so complicated and requires periodic review:p

I replaced mine last July and I will do it again this year. I have no idea as to how long it was before it was replaced. Liberty may have replaced it 2 years ago when I acquired the coach from them. I would have to check the records. I think though that I will just replace it annually.

It is easy & safe . Mine is located at the top front of the opening after removing the passenger side rear fender skirt and requires no under coach efforts..

As suggested elsewhere, bleed the system down first.

Jim, I for one love pictures keep them coming. They great for us simple minded people.