Air Pressure Drop?

[Joe Cannarozzi]

Good job.

What about your aux. air pressures?

[jimshoen]

Hector,
Very impressive. How does the bubble system work? Did you already post about that? Please direct me to it.
Thanks

[Jeff Bayley]

Jeff did make a statement that may lead a Prevost owner to draw an incorrect conclusion. Once you have turned off the key on your Prevost (except for some very old coaches) the air in the air bags should be "locked" in the air bags unless the air bags, the Norgren valves or their respective fittings are leaking. The auxiliary air system pressure can go to zero, every device that uses aux air including the step cover air cylinder can be blowing air from it, and the bus should not lean.

Jon and all- This set up Jon refers to was noted and discussed on about day 3 of the dum and dummers head scratching. At what year Prevost changed over and make this "check valve" type of set up to lock the level in place or prevent the bags from dropping (even if the aux air went to zero).....I don't know what year they changed over, but my 97 Roayl on a 95 Chassis, didn't have it yet. They said that I had changed about 80% of the parts that would now allow my chassis to have one or two more components changed and mine would have this check valve (for lack of a better term) type of set up.

As regards the cost, it was in excess of $4,000 and looking back at it now, I should have refussed to pay for all the un-needed parts but I was too pre-occupied with working on the computer and the phone to make a sale to scrutinize and question it. Now that I've gone on to hear more stories like mine, I'll be less of a push-over hopefully. Joh is correct that you have to lead the mechanics around with a bull nose horn and watch what their doing. Mechanic leaves to go get a simple part and where do they dissapear to for 20 minutes ? If I thought they were checking the POG archives for answers I wouldn't mind paying for that.

[Jon Wehrenberg]

Not true Jeff. Your coach should not drop in the rear if aux pressure goes to zero (easy for you to check) and if the key is "off" the air in the bags when the key was turned off should be retained (unless there is a leak). The change was made prior to the dates of your chassis I think.

[Joe Cannarozzi]

Jim it looks like he made it out of a canister for a fuel/water separator. Fashion a tube to get you close to the bottom and put enough water in it to cover the outlet of that tube. It is simply inserted in line at any given point supply air and look for bubbles.

[phorner]

Good job, Hector and a great post. Thanks for taking the time to detail everything with the pictures.

[Jeff Bayley]

Hi Jon- Hmmmm. Strange. So you mean to say that this change was like before 1990 or so or maybe the mid 80's ???

My coach wasn't keeping good level for more than 2 or 3 days prior to this leak on the converter installed sliding floor board being fixed. Then the leak became a lot worse and it was falling after about 12 hours and it had to be addressed. After the replacement of that part (and all the other parts that probabley weren't bad but MIGHT have been letting some air out), now it stays level for at least a week if not 10 days but after about two weeks in the front yard, it eventually falls. If Jon is right and my 95 chassis has this up to date provision, then I suppose the answer is that even in a best case scenario, the system somewhere or another (small leak around bag connection itself ?) is responsible for it eventually falling. Does anyone have a bus that will stay level for more than a month ? I'm thrilled to get 7-10 days out of mine compared to where it was at before anyway.

[Jon Wehrenberg]

Jeff on all but older coaches, (up to about 1990 or maybe a little later) the aux air pressure can be zero and the air bags will not deflate, except when there is a leak in the suspension system itself.

Jeff, if your bus is staying up that long you have an excellent system. The Prevost standard for acceptability is 3 days.

[dreamchasers]

Jon,

My 95, on a 94 chassis, dumps the tag axle on loss of aux air. I have traced the pneumatic drawings for my coach and think I know the reason.

On the passenger side-rear, accessible through the access door in front of the chassis battery access door, a pneumatic cluster in located. This manifold is sourced by the aux air system. Through a 24 volt relay I think (Have not checked out that portion of the logic yet) is controlled by the Allison Transmission (After obtaining a speed of 15 or greater, the 24 volt relay is activated, routing supply air to the Norgren), air is routed to the supply of a Norgren that controls the tag release. When air pressure is loss on the aux system, supply is lost to the Norgren controlling the tag, and air is released from the tag through the loss of aux pressure, via the Norgren supply. I have looked at this in detail and this could be worthy of a seminar. It is so simple it is complicated.


Your statement that pilot air is de-energized (with the key off) to the Norgrens is correct for the front and rear duals. It get tricky on the tag axle logic.

The tag axle dump upon loss of aux air will happen on a 94 chassis (It does on mine.)


Hector

[dreamchasers]

Concerning the 'air bubbler', I do practice the 'KISS' principal whenever possible. With the complexity of the pneumatic systems on these Prevost coaches, using this air bubbler takes much of the complexity out of troubleshooting air leaks. With the dynamic complexity of the Prevost pneumatic systems, I needed a sure way of checking for leaks, internal or external. It either leaks or it does not!

I am on my second version of this device and I used it recently to uncover several very small leaks in the braking system.

pog leak detector 2.pdf
This is a drawing of the air bubbler. On this version, I purchased parts at a local Lowes. The part numbers are item numbers from Lowes.

pog leak detector 2 text.pdf
This is instructions and my disclaimer. Use at your own risk!


harbor freight regulators.jpg
This is the regulator set I purchased from Harbor Freight. I disassembled the set and used the regulator and the air filter component.

bubbler.jpg
This is completed bubbler. It is one of these things that looks bad, but feels good. It works for me.

I am sure a version 3 will be forth coming. If I were to offer needed improvements, first the check valve I used is a ¾” water check valve. It uses a rubber seal, which is good. The check valve can be upgraded to a smaller check, and mounted closer to the bubbler. The check valve is needed for when the operator reduces the air pressure on the regulator. The check is needed to prevent the water from being ‘backflowed’ through the bowl and into the regulator, ruining the air regulator.

I used Permatech thread sealant for all threaded connections. The ½ “ copper pipe was available from Lowe’s, thus I used it. Sweating the copper pipe together proved for an air tight connection.

In order to get the bubbler to seal, I had to smooth the surface of the o’ring seals on the metal flange with a flat file to get a good seal at 100 PSI. I also lubricated the o’ring and used a pipe wrench to tighten the flange on the bubbler to get a seal. Additionally, I cut the bottom portion of the bubbler metal protector in order the have a clear view of the tubing extending in the water. A dip tube is installed in place of the filter and the housing assembly is reversed (the inlet becomes the outlet) in order to have the flow in the needed direction.

Use of this device should be done by qualified personnel only. Working on Prevost suspension systems can and will cause unexpected results, causing the coach to lower unexpectedly. The suspension must be supported by approved jack stands before working of the suspension components. In other words, don't use this unless you totally understand the results of your actions. This device is for the personal use of POG members only and is not to be use commercially without express written permission of Hector Duplichen. Whew!

Hector