Air Pressure Drop?

[dreamchasers]

What is a reasonable amount of air pressure drop during a 24 hour period on the main and aux air gauges on the dash? I am trying to 'tighten up' my air system.

Thanks,

Hector

[Steve Bennett]

We have had coaches that will stay up for 30 days plus with 0 air loss. Most will loose a couple of pounds per day on the aux system, but very little on the brake primary & secondary tanks. The colder the ambient air temperature, the quicker the air loss will typically be do to the contraction of the fittings. If your coach has an auxiliary air compressor, we feel it should not need to run more than once a day in normal climate.

[Joe Cannarozzi]

Hector this is a great question. Steve beat me to a responce but looks like we agree to a great degree.

DOT allows up to but not more than a 20psi drop in 10 minutes. That is with the brakes released. IMO that is ridiculous and bordering on unsafe and I am pretty confident no one here is anywhere near that bad.

So what you are asking is slightly different and want to know an acceptable amount of pressure drop with the parking brakes on.

IMO we are going for no loss at all.For perspective, I think if you can keep the aux air compressor to cycling once a day (if not using any pnewmatic accessories that would skew the loss levels) you are probably about average compared to the rest of the group.

Our bus was pitiful when we got it and would completely bleed off overnight.
I got it to the point that it would take a week until the suspension dumped. I know of other issues but do not have the doe to correct them. When I do I expect to see at minimum 100lbs indefinitely, at least that is what I strive for.

This is one of those issues for me. I have driven truck my whole life and was completely comfortable with reasonable or slight loss of pressure overnight. However since joining POG and being influenced by the likes of Jon that is no longer the case. There is no reason why given a reasonable amount of time we can not get these campers air tight or darn close to it.

So how about it Hector what kind of loss are we talking about here, Hmmmmmmmmmmm?

[dreamchasers]

Hector this is a great question. Steve beat me to a responce but looks like we agree to a great degree.

DOT allows up to but not more than a 20psi drop in 10 minutes. That is with the brakes released. IMO that is ridiculous and bordering on unsafe and I am pretty confident no one here is anywhere near that bad.

So what you are asking is slightly different and want to know an acceptable amount of pressure drop with the parking brakes on.

IMO we are going for no loss at all.For perspective, I think if you can keep the aux air compressor to cycling once a day (if not using any pnewmatic accessories that would skew the loss levels) you are probably about average compared to the rest of the group.

Our bus was pitiful when we got it and would completely bleed off overnight.
I got it to the point that it would take a week until the suspension dumped. I know of other issues but do not have the doe to correct them. When I do I expect to see at minimum 100lbs indefinitely, at least that is what I strive for.

This is one of those issues for me. I have driven truck my whole life and was completely comfortable with reasonable or slight loss of pressure overnight. However since joining POG and being influenced by the likes of Jon that is no longer the case. There is no reason why given a reasonable amount of time we can not get these campers air tight or darn close to it.

So how about it Hector what kind of loss are we talking about here, Hmmmmmmmmmmm?

I am definitely leaking, but I am aggressively tightening thing up.

I believe I have a leak on one of the many braking components located under the coach. Here's my reasoning. After rebuilding the Bendix AD-9 Air Dryer, I started the coach to build pressure. After the 125 psi control spitting of the air dryer, I let the coach sit all night and the next morning, still 125 psi on the main air, Hurray!!. Not so fast, today while replacing and testing other components for leaks, I pumped the brake pedal a few times to consume air and build pressure back to the max. Now I notice, I am leaking again. I will test some of the braking components tomorrow.

I predict when I go out to the coach in the am, I will have lost 50 psi in 12 hours. When I pump the brake pedal, I can hear air discharging when the pedal is released. I am sure one or more of the exhaust ports are leaking.

What do you recommend on the troubleshooting the braking components? Any magical ideas or things to avoid.

On the suspension side, I have corrected several very minor leaks and it is looking good (cracked fitting on the new air bag Prevost installed). I am using a home made pneumatic tester for checking leaking suspension components. It works great!

I also replaced the check valve in the main air tank and the check valve in the aux air tank. I am working my way through the braking system.

Hector

[Joe Cannarozzi]

It is normal for air to exhaust as you release your foot from the pedal. If you are holding the brake pedal down steady and you hear air leaking THAT is bad.

For those who missed this procedure before it is definitely worth repeating.

Testing air pressure and looking for leaks as a standard pre-trip check. If you want to be sure you are safe you should be doing this every time you start a day.

First:
Build up air till the air dryer goes off and the compressor stops building pressure, with the parking brakes on. Wait 10 minutes and record the drop.

If you have a loss here it is going to be aux. air or possibly service air too.

Next:
Now first release the parking brakes pump the brake pedal to get the pressure down far enough to get the compressor pumping air and again build up to 120. Wait 10 minutes and again record the drop but this time you have the parking brakes off.. (The DOT allows up to but not more than 20psi drop in 10 min.)

If an additional drop is observed from the initial test you have an emergency air leak. ( probably a maxi or a line going to it)

Finally:
again with parking brake released and air built up to 120 step on the brake pedal and hold. Turn the bus off and open a window to help you listen along with watching the gauges.

If you hear air leaking but only when you are applying brake pressure it is Service air. (IMO anything heard during this test is unacceptable)

In conclusion the easiest way to completely rid yourself of pressure loss is to first get it to hold air with the parking brake on. When you get to there then release the parking brake and again get it to hold.

I can't tell you how many times I have got to the end of a search confident I have finally found all the leaks only to come out the next day and see pressure loss, go over things again and find more. This project is a lesson in perseverance and one worth doing for sure.

[phorner]

Joe,

I like your attitude about zero pressure loss!!

Can't wait 'till you get your hands on our bus....:D

[lewpopp]

Hey Joe,

You are short on "doe"? Instead of using "doe", try using Lewbucks or DOUGH. If that doesn't work, use a buck or a fawn. Good ole Lew, trying not to miss a chance.

[Orren Zook]

Hey Joe,

You are short on "doe"? Instead of using "doe", try using Lewbucks or DOUGH. If that doesn't work, use a buck or a fawn. Good ole Lew, trying not to miss a chance.

I'm sure it was a Freudian Slip - hunting season has arrived in the midwest

[dalej]

Now I notice, I am leaking again. I will test some of the braking components tomorrow._Hector


When your coach is sitting in the park position there is no air going into any of the brake lines or chambers. There is air pressure from the brake tanks sitting at the park brake valve and the foot brake control valve waiting to be used.

[truk4u]

No air leaks.... You guys are dreaming!

[Alek&Lucia]

No air leaks ?????
Sure, anything else, perhaps Santa Clause ?

[Joe Cannarozzi]

Truk I said some things like darn close to it and that is what I strive for and how it is a lesson in perseverance.

Alek didn't your bus get to be 8 years old before it started showing leaks?

I remember Orren posting that his will hold air indefinitely and they have an old one. I look forward to the day I can do some more with ours.

What is the alternative? The heck with it? This chore is a hard one so lets find something easier?

I know let's polish the rims.

[Jon Wehrenberg]

I have a slightly different explaination than Joe. He can jump all over me if I am wrong.

First....understand my coach, and almost every one owned by POG members has two air gauges, primary and secondary brake. Very few if any have a dash mounted aux air pressure gauge so this discussion is limited exclusively to what can be diagnosed from the driver's seat and in essence is a pre trip brake check.

With parking brake engaged, foot off the service brakes, air system up to max pressure, turn off the engine. The two systems should not lose any pressure. Not in one minute, ten minutes or even overnight because as stated in a previous post there is no pressure on any of the braking system beyond the relay valves. If any pressure loss is detected it should be corrected. 20 PSI in ten minutes of pressure loss is substantial. Steve has it right. A coach should sit for days if not weeks before a loss in pressure is noted.

Now, with the pressure up, engine off and wheels chocked, release the emergency brake. There should be a slight drop in pressure as the spring brakes are released and the pressures should stabilize and stay without dropping. If there is any pressure loss beyond the initial loss the emergency brake diaphragm(s), hoses, or fittings may have a leak and it needs to be repaired. Leaks in the emergency brake release part of the system will grow larger and to the point where you may be shut down.

Assuming the emergency brake release does not show any additional pressure loss, step firmly on the service brakes, and hold the brake pedal. Again, there should be a drop in pressure momentarily, and then the system pressure should stop dropping and hold steady.

If no pressure drop beyond the initial drop is noted after a period of time (a minute or so) alternately apply and release the brakes. When the brake system pressures drop to 40 or 50 PSI the emergency brake knob should spring back to the brake applied position and the emergency brakes should again be engaged.

That completes the brake system checks for leaks and problems.

The aux system is totally independent and the leakdown rate and methods to diagnose leak sources is a topic for another thread, and it is doubtful if anyone has any real definitive answers for that topic.

[Jeff Bayley]

Here's a cut and paste I put on this topic on a prior occasion.

---------------------------------------------------------------------

Related to this topic, I was at Prevost NJ for 3 days solid while they tried to track down why by bags were falling and the coach wouldn't stay level. After replacing one part after the other including the Norgren valves there was still no improvement but I got a lot of "Well, those were bad anyhow and also needed to be replaced". On day 3 or 4, I was letting myself into the coach and I heard a hissing noise. I got the so called mechanics attention to it and after further investigation, it was found that the air operated strut that works the recess floor was leaking air and that strut was defective. This was a converter item and Royal had tied it into a part of the air system that was directly tied into letting the air bags leak out and fall.

For what it's worth to the issue of problem solving and wasting money.

[truk4u]

Good post from Jon about brake air and I think most of the colorful remarks about air leaks (including mine) were directed at the Aux system. If your Aux air never leaks down, please make application to Guinness Book of Records or click your heals together and keep repeating, " there's no place like home, there's no place like home!):D

[dreamchasers]

I see the topic of air leaks are close and dear to all Prevost owners. I currently have my coach sitting on the great jack stands that Jon designed and had made. They work great!

On my Country Coach, I had to remove the coach AC condenser to have access (What a pain!). But once it is out of the way, WOW, I can actually reach things. I would advise any Country Coach owners with the Fridgi-Cool AC system, if you are considering any serious work in the area in front of the 'pumpkin', consider removing the condenser coil for better access. Plus, while it is out, I will replace both electric fans on the condenser as preventive maintenance. I am an R12 user, so I purchased a 30 pound keg of R12 from Ebay. I got the idea for the R12 Ebay purchase from Ted Delorme. Thanks Ted.

With the coach safely supported, I am methodically checking all the air circuits. I will advise what I find when complete. I am taking plenty of pictures as I go.

Hector

[Jon Wehrenberg]

Here's a cut and paste I put on this topic on a prior occasion.

---------------------------------------------------------------------

Related to this topic, I was at Prevost NJ for 3 days solid while they tried to track down why by bags were falling and the coach wouldn't stay level. After replacing one part after the other including the Norgren valves there was still no improvement but I got a lot of "Well, those were bad anyhow and also needed to be replaced". On day 3 or 4, I was letting myself into the coach and I heard a hissing noise. I got the so called mechanics attention to it and after further investigation, it was found that the air operated strut that works the recess floor was leaking air and that strut was defective. This was a converter item and Royal had tied it into a part of the air system that was directly tied into letting the air bags leak out and fall.

For what it's worth to the issue of problem solving and wasting money.


Everybody here should give Jeff a huge "attaboy" for what he posted because he has pointed out clearly why as a prevost owner you need to take control of the process of repairing and maintaining your coach.

What Jeff did not post was the costs associated with several days of chasing leaks and replacing a few parts. What he did post was the direction a repair facility will go if you bring a problem to them and not specifiy how you want it addressed.

First, all air bags and all associated Norgren valves will cost less than $2,000 and to replace them all will take no more than 2 days or about 16 man hours of labor. Instead of paying for three days of a mechanic's time to diddle around looking for leaks, bite the bullet and replace all the parts if the system hasn't been repaired or replaced in a long time. It will be cheaper and significantly better in the long run.

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.

And just for purposes of clarity, our suspension system is really not a suspension system to be viewed as a whole, but as three separate suspension systems (front, left rear and right rear) that operate in unison when on the road, or individually when leveling the coach.

[dreamchasers]

At last!!

It was a battle, but the sweet smell of victory is in the air. My brake system's air pressure has been holding for 5 days without dropping a pound. Hooray!!

First, I rebuilt the air dryer for good measure and to assure the supply system was in good order.

Using the bubbler system that I mentioned in Seiverville last year, I was able to find four air leaks in the brake air system. The biggest leak was in the Brake Spring Valve. This device controls the brake air to the front brakes. I replaced it with a new one. I had a very small leak in the 'push to fit' fitting on the back of the secondary air gauge mounted in the dash. The next leak was in a 1/8" union on the tubing going from the aux air cluster (connected to the double shuttle check valve). It was a tiny leak. To my amazement, the air pressure gauge had a very small leak internally. Whew!

Now the brake air system is bubble tight!

3805
This is the brake spring valve located below the drivers compartment. I was able to access the unit through the front slide out drawer, behind the bumper. It was leaking out of the exhaust (black rubber cover).

3806
After removing the spring brake valve, I started removing the fitting and components to be placed on the new assembly

3808
The push to fit fitting on the back of the dash pressure gauge was leaking. I replaced with a new fitting.

3809
I am still amazed that I was able to find the small leak in the dash pressure gauge.

3807
This is a photo of my homemade bubbler. It monitors all the air going to the components. As you can see, the slightest leak in detected. See the small bubble. I was testing the gauge and this bubble would form over a 45 second period.

[dalej]

Great job Hector! You have done a good job there.

[Orren Zook]

Congratulations on tracking down your leaks Hector and nice job on the step by step photos too!

[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.

3811
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.

3812
This is instructions and my disclaimer. Use at your own risk!


3813
This is the regulator set I purchased from Harbor Freight. I disassembled the set and used the regulator and the air filter component.

3814
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

[Jon Wehrenberg]

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

If I am correct, that is the system that is tied into the stabilizators to prevent the tag from lifting above a certain speed.

If that is the case there are very few of us who have that system still enabled. To the best of my knowledge you, Jim C and I have that system. Prevost has been disabling the system.

[Yankee802]

First, I'm not sure I understand how that bubbler thing detects air leaks, but I can find air leaks REAL fast with dish soap and a spray bottle, and it's cheap and easy.

Second, I guess my coach is of the vintage that does not have the lock in the airbags to keep them level. If my aux tank goes to zero, my bus is on the ground. I discovered this when a friend showed me how to bleed the aux air tank of water, man it was RED, almost like blood spraying out of that valve. I'll endavor to do that once a month. Also, my coach will ever so slowly sink down, albeit level, over a week or so. I haven't checked the air brakes, but after reading this thread, I'll do Jon's test. I have noticed that after almost a month sitting, when I start her up for her montly run, the air pressure in the dash guages are in the 60ish pound range, if memory serves.

Geoff

[Jon Wehrenberg]

Geoff,

Soapy water is only one method of finding leaks. When you get into chasing leaks you will find other methods are required due to the nature of where leaks can occur, a lot of locations requiring sophisticated devices because the leaks are internal.