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Capt………….

Our coach air system must be kept dry and free of moisture. I can go into detail regarding the potential damage that can occur if the system is allowed to accumulate moisture, but all I need to say is it can prove expensive and might compromise your safety.

Every air system whether it is on a Prevost or a truck or a conventional RV requires periodic maintenance.

Our coaches maintenance schedule calls for chassis lubes at about 6200 miles. This is the perfect time to drain the coach’s air tanks. While the coach is being greased draining all the air tanks is quick and easy. Every couple of years is the only other scheduled maintenance that I would recommend and that would be the replacement of the air dryer cartridge. Doing that will keep the air system dry.

The only caveat is if the coach is not driven much, but is allowed to sit with the auxilliary air compressor on to maintain aux system pressure then the system maintenance must include routine draining of the water trap or separator downstream from the aux compressor. If that is not done condensate from the aux compressor could find its way back into the coach’s aux air tank.

Any time you or a tech has an opportunity to go beneath the coach take advantage and open the petcocks on the coach air tanks. Let them drain completely and you are assured you have removed any water that has the potential to migrate into the various air systems. In the first tank which is often called the wet tank you may see a water / oil mix. This is normal because oil can pass through the coach engine driven air compressor. If you see oil coating the area of the coach frame near the bottom of the air dryer that is a sign you need to change the dryer cartridge. You should never see that oil if the air dryer is properly maintained. That is a result of oil bearing air coating the desicant in the air dryer cartridge voiding its ability to remove moisture from the compressed air.

When the tanks are drained you accomplish one important task. If you drain them in sequence each succeeding tank will retain pressure proving the check valves and protection valves are functioning. This is an important check because it proves if you have a catastrophic failure of an air hose for example, the balance of the air system will remain intact and functional.

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WOW…thanks Jon. I was trying to crawl around underneath the coach a couple of days ago and there is no way I can fit under there…I had read that some air brakes have a handle to pull to drain the moisture on them…it actually says to do it daily. Another read I found stated that some have automated drains on them ( I have a shop air compressor like that)…I would be more than happy to grease the fittings and do the maintanence if I could get underneath to do it. I know the fender skirts are removeable, I wonder if I can access the tanks by removing them…? Thanks for the info…very useful.

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Kelly,

You
can reach the wet tank and primary air tank by lifting your fenders,
but no way to do the secondary and aux tank up front without going
under. Don’t ever get under the bus unless it’s blocked and braced.
Your aux tank should have a Norgren water separator in the steering
bay that you can drain, but the tanks need drained every so often. I
usually put a lanyard on the wet tank so I can drain often, but
haven’t yet go to it on this bus.

[JIM]

Wow, I’d like to be able to spend a couple of days with you and my bus in the shop Jon…It would be very educational and I could learn a lot about my ride l!!

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Jon you mentioned draining the tanks in sequence. Is the sequence self evident (wet tank and follow the lines ) or is there something I should reference to make sure of the order ?

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If you really want to crawl around under your bus to drain air tanks, perform maintenance or just plain ” check stuff out” it can be a rewarding experience.

Just be absolutely clear that you NEVER, EVER get under your bus without it being properly supported on stands….not even once, or only a “little bit” under.

There is absolutely no room for error, literally. Once the bus is aired up and placed on supports, there is a surprising amount of working room underneath.

Again, NEVER get under your bus without proper support.

[Tom]

I am not sure if there is a sequence to tank draining, but I usually do it when I lube the chassis and I start at the front.

I drain the aux tank first. The reason for that is if I have a failure of an air line or air bag in the aux or suspension system I want to know I have retained brake system pressure. I then drain the secondary brake system tank.

Then when I am greasing in the rear I drain the wet tank and the primary brake tank. As long as I have pressure in each tank I believe my check and protection valves are doing their job.

A few comments….Hector taught me to lube the tank drain valves so periodically I do squeeze some rubber lube (I use white lithium grease) up into the petcock and that helps make the petcocks easy to turn without damaging the seals.

Also, I expect all my tanks with the possible exception of the wet tank to be dry. If there is moisture in any of them I am going to service my dryer whether it is due for service or not. My tank draining is about every 5000 miles due to my lube schedule so there should be no moisture. The wet tank might get an oil water mix, and it might be a spoonful or less. I drain every tank completely because the air pressure will blow a path through the water if any and you really will not see the moisture in the tank until the pressure reaches zero.

And I have a pit in my garage, but as Paul has pointed out, I still support the coach on stands. Never ever even think of getting under the coach unless it is supported. NEVER EVER.

This may be considered sandbagging but if you think you are using knowledgible techs to service and maintain your coach pay attention when they are beneath the coach. If they lube the grease fittings and look like they are doing other things, just note what they are. As far as I am concerned a tech isn’t worth taking a coach to if when he has the opportunity to be beneath the coach he isn’t inspecting the brakes, checking for rubbing or chafing hoses or air lines, looking for evidence of hub seal leaks, and he is only applying enough grease to clean fittings to get grease into the joint, not so much it leaks and dribbles out. And finally he drains the air tanks. If he is doing all that as a routine part of your service without even being asked, he is a keeper. If you have to tell him any of that he isn’t doing his job. I have been beneath more than a few coaches whose owners have bragged about how good their maintenance has been and I see evidence whoever was doing the maintenance wasn’t good enough to oil my bicycle chain. You need to watch and ask questions and make the tech know you expect good work.