No air in rear air bags - 1997 Prevost XL 45-E

OneLapper · July 18, 2016, 07:22:00 PM

The problem: Lost air in right rear air bags the other night. Last night lost air in the left rear air bags. The rear of the bus will not air up.

Bus is at a shop right now (24/7 service dept, kinda cool concept) and the technician says the rear air tanks are empty. Since it's a truck shop, they claim they dont have the right type of valves in stock, so they don't want to remove, inspect and clean, etc. any valve. If they break it, they can't fix it.

Bus has to be back in service by 10pm tomorrow to make it to the next venue.

Does anyone have a suggestion on which valve it might need? Or valves? I'm pouring through the parts manuals and I've never seen a piece of equipment, wheels or no wheels, that use more air valves than this thing.

Thanks,

Mark

luvrbus · July 18, 2016, 07:56:04 PM

Fill the rear tanks with a shop compressor it may start working again,you can always buy a compressor at H/D to keep the rear air up till you can get it to Prevost,it's not unsafe to do that all you are airing up are the auxiliary tanks.Aren't the Prevost a over engineered air system

DoubleEagle · July 18, 2016, 08:15:45 PM

Has your air dryer not been serviced for some time? There might be a lot of sludge in the system that is fouling up the transfer valves and check valves. The mechanics where you are at should be able to check the air dryer. Hopefully, there are connections on the rear tanks so you can air up.

luvrbus · July 18, 2016, 08:33:34 PM

You can remove the drain valve to air it up, the accessory tank is up front on the right side it may have another about the middle on the right side

OneLapper · July 18, 2016, 08:45:38 PM

I'm certain the dryer hasn't been serviced. I'll have them look at that.

Cliff, you got me thinking.... I wonder if I can get the tech to run a line from the front aux air tank to the rear tank that feeds the rear air bags. I think I saw that the air bag system has a pressure protection valve that limits it to 75 psi, or maybe it maintains a min of 75 psi. Now I need to reread that section of the manual.

I have spent three days convincing three different "mechanics" to think out of the box and just FIX it! If you can't get the part, then improvise. Example, they missed the shipping cut off so they "can't get the part tomorrow" (BTW, I gave them the part number they needed to order 5 hours before the shipping cut off, I insisted that they order it next day AM delivery, I was told they would order, but they didn't) . So....... I found someone in the area to get a Uber ride, pick up the part, then had the Uber driver drive it to shop. Just like that, the part they couldn't get, is there. Getting them to install it is a different matter.

eagle19952 · July 18, 2016, 09:11:07 PM

run a line from the front aux air tank to the rear tank...
that could compound your troubles.

Clifford's suggestion to plumb an auxiliary compressor is best.
do you have an inverter ?
a $100 bill gets a pancake.
i would.
i have.
just don't return the compressor and tell about it here

niles500 · July 19, 2016, 01:28:04 AM

Your problem is probably a norgren. valve - FWIW

Jon · July 19, 2016, 03:58:17 AM

The real problem is it is in a shop that services trucks and not a shop that actually understands Prevost suspension systems. It isn't rocket science, but some shops have the ability to think they know the system, or at least more than the bus owner and they will screw with the system, usually ignoring the true problem until the owner's wallet is empty.

The suspension air bags have NOTHING to do with the wet, primary or secondary air tank, except that they need to have air in them before the accessory tank gets air. The accessory tank is the source of air pressure for the suspension. Fill the accessory tank (only) from the schrader valve in the steer compartment, and with the key on and the suspension control set to the driving or road position the rear should air up. If it does not you likely have an issue with the solenoid valve in the center on the 5 valve manifold near the schrader valve. If it does air up, look at your compressor or protection valve.

robertglines1 · July 19, 2016, 04:41:26 AM

Jon beat me to it. Mist have signal to center stack solenoid, front left lower steering compartment. what it does is change elect signal from switch to air signal that sends a air signal to norgren valve behind last bay bulkhead in front of rear axle. that valve either directs air to level low or manual leveling valves.. Also the front opens valve to fill aux tanks. Not unusual for this filter to be neglected to the point of plugged up. Go to prevostcommunity web site at top articles section go down till you get explanation of level low. I don't think you have to sign in to get there. Bob

robertglines1 · July 19, 2016, 04:43:57 AM

PS all valves in that stack are interchangeable. If you may think the center is bad just switch solenoid from. another .

luvrbus · July 19, 2016, 05:57:48 AM

Mark, there is a regulator from the auxiliary tank at the right front corner not far from the tank they go bad too,what I was trying to say if you can equalize the pressure on both sides of the protection valve most of the time it will start working again.The entertainers coaches that come through here carry a box full of valve, fittings and lines to bypass some of the valves when they have a problem on the road,lol if I ever need a NG valve I just look for a entertainer coach

niles500 · July 19, 2016, 06:38:25 AM

I ruled out solenoids because it would be rare for 2 to go out at the same time - FWIW

Jon · July 19, 2016, 08:09:13 AM

Any time there is an issue as described the only way to resolve it is to find out where there is a lack of flow. If you have aux pressure then you have to follow the air through both the manifold which is sending the command to the Norgren valves, but also to the air supply to the Norgren valves.

In a Prevost the air bags get air routed through 5 port Norgrens which are normally closed until they get an air signal from the manifold stack. Then based on the signal which is going to come from those solenoid valves the Norgren which is normally closed, is going to allow air flow through either the ride height valves, or by manually filling with commands through the level low system controls. Without leaving the driver's seat you can do part of the diagnosis by determining if you can get the rear to raise using one of the two methods. If it won't raise at all then you have to see if you have an issue with the air supply not reaching the 5 port Norgrens.

If the air system has not been maintained and the norgrens within the system are filled with moisture and aluminum oxide which becomes a paste almost you have a whole coach issue of fairly large proportions. But if the system is dry and has been maintained you may just have a problem with on valve.

luvrbus · July 19, 2016, 08:24:54 AM

He is lucky his is a 1997 model these new Prevost with the computerize air suspension are a nightmare.
A casino here has a H with the self closing door it take 4 Norgren valves to close 1 door and it is interlocked to the B500 and won't engage till the friggn door is closed why they do stuff like that is beyond me

brmax · July 19, 2016, 09:20:21 AM

I totally understand Clifford, recalling some of the air circuit boards on the frames of the dumps trucks in the mid 2000's with their electric over air relays controlled by the body control module. This was a real blessed learning curve, and with out the laptop and some software it was a pain at times. I had fun talking with a friend who work with the city trans busses and I felt lucky.

Floyd