Air Bag Bench Test: how do I do that?

Deb and I replaced six rear air bags on our 1991 Angola. We did not bench test any, figuring Prevost would not ship one which leaked. We were wrong. Ordered a replacement for the one which was leaking and installed it. Suspect it might be leaking, too, but can't figure how we might be recipient of two faulty bags.

If we conclude it is leaking, I want to take it off and "bench test" it, but I don't know what that means or how to do. I have a "bench," so that's where I'll test it. Other than a bench, what do I need?

Exactly what do I need to accomplish this? I think I'll have to buy gauge and fittings, but don't know which ones. I live about 15 minutes from a NAPA, and we have Fastenal, Advance Auto, AutoZone, and a privately owned auto parts store. I imagine I can get what I need there. I also have big compressor with plenty of air power.

If there is an article which any of you know of which says, "Here's How To Bench Test Your Prevost Air Bag Prior To Installation So You Don't Have To Install It More Than Once," please direct me to that and I'll see if can figure it out from there.

In advance, thanks.

eric faires
huntsville, TN

Eric

I have never done this but it seems easy enough.

I would first build a box around it. Like a 2 by 4 frame around it so when you air it up it isn't extended all the way out.

Thread a T into a nipple and into the air inlet on the top of the bag. Thread a pressure guage into one opening and a female quick coupler for your air line into the other.

Put about 40 lbs of air into it and unhook the air line from the female coupler. First do the soapy water treatment then see if it bleeds down over time with the air pressure guage.

Finding small air leaks are always a challenge, weather on a Prevost or other pneumatic systems. Joe's idea will work, but you might consider filling a 5 gallon bucket with water and pushing the inflated air bag underwater to see if you see any air bubbles. If you have a leak, submerging the air bag under water will find the leak. I think Jon has done air bag bench test before. Perhaps he can help with what he did to confine the air bag and at what pressures.

If the air bag is still mounted, then things are a little more complicated.

Status:
The bus barn slab is poured and the driveway modifications should be completed this week. I am working on temporary electrical now.

Good Luck,

Hector

Quote:

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Originally Posted by Joe Cannarozzi

Eric
I would first build a box around it. Like a 2 by 4 frame around it so when you air it up it isn't extended all the way out.

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Couldn't I just lay it on its side? I don't mind building a box or frame for it, but wonder if I need to do that.

I'll go by NAPA tomorrow to see if they have the parts (I bet they do).

Thanks for guidance.

eric faires
huntsville, TN

Sure you could. Watch how much pressure you put in it. Carrying a load under the bus they are around 60 or 70psi but I would not go nowhere near that bench testing without that jig.

I thought the jig would duplicate the actuall configuration better. Sometimes what is leaking at 60psi will not leak at 30.

I would be concerned what may happen at the bottom where the bag attaches to that base if allowed to just stretch out but I may be worrying about nothing.

If you have one of the old ones experiment on one of those first.

I have a fabricated steel fixture you can use Eric. I made if back in the old days when the air bag tops popped in. I used it to pressurize the bag to seat the top and check for leaks.

With the air bag in there and a valving arrangement (that you will have to make) to seal the air bag off you can leave it pressurized and roll it around in a big tub of water. I also have the tub.

Did you check your leveling valve(s) on that axle? It's pretty easy to see if one is exhausting when it shouldn't be and easier than swapping out a bag. Just put the exhaust hose from the leveling valve in a glass of water and see if it is making bubbles, in a level condition there should be no air escaping from the valve's exhaust port

Orren,

I have some knowledge of where Deb and Eric are on this puzzle.

The issue is isolated to one side, rear. It was further isolated by lifting the tag axle and finding that stopped the leans. By doing that it eliminates all potential sources of leaks to a leak on the tag axle side of the 3 port valve between the tag and drives, all the fittings associated with that, and the air bag.

The new air bag was found to be leaking around the top crimp. I am assuming that air bag has been replaced with a new one and the defective new one is on its way back to Nashville for credit. If the coach continues to lean, which is sounds like is happening (assuming the tag lift exercise is repeated with the same results) it brings the 3 port valve, the fittings and the replacement air bag again into question.

If Eric borrows my air bag cage and finds the air bag to be OK my advice is to drive it and see if exercising the valves blows the gremlin out of the system. If the air bag and fittings are OK it could be as simple as a bit of dirt at the O ring on the spool valve that just needs to get exhausted out through use.

Quote:

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Originally Posted by Jon Wehrenberg

Orren,

I have some knowledge of where Deb and Eric are on this puzzle.

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Jon stated it all correctly, and has more than "some knowledge" of where we are. He has guided us every step of the way, and did a whole lot of work on our bus in addition to his supervisory role where he just wanted to watch Deb and me get greasy.

Tonight is tag axle lifting time (again), to see if can isolate the problem (again). We already replaced the three port Norgren, and this is the second bag at the tag (I can rhyme as well as Loc can pun, maybe better).

Thank you all for help.

eric faires
huntsville, TN

What I watched was new owners really get into developing an understanding of their coach. Neither Deb nor Eric shied away from diving in to update the underside of the coach, and while there may still be some things under there for them to learn I can say they are experts now in the topics of the suspension and the brakes.

They have replaced air bags, Norgrens, brake chambers. helped with hub seals, chased leaks, and most importantly correctly analyzed where leaks could be, and did a 100% lube and fluid change in exact accordance with the Prevost specs. Very impressive.

Hey Eric, can you tell us any good jokes? Oh, I forgot, this forum is not censored.

So Eric, what happened with that bag and that leak. You cannot just leave us hanging.:rolleyes:

What about that bench test?

So now to be completly sure one has to pretest bran new components? Sheesh. What kinda crap is that? Thank you Mr. Firestone.

I think the airbags were BFGoodrich, but you are right. They shouldn't leak.

Eric and Deb picked up the airbag cage and a big tub last night. If the second new airbag is found to leak this brings a whole new dimension to the difficulties in tracing a cause for the leans. It is relatively easy to find a leak in a fitting, less easy to isolate a leak in a Norgren valve, and very difficult to find a leak in an airbag.

For those who are not aware, unless an airbag leak can be detected with soapy water (remember, unless you pull the wheels and front drive axle fender liner only 1/2 the airbag is visible, and none is visible at the bottom) there is no other way to find an airbag leak while it is installed.

That means the best and only way is to remove the airbag and inflate it, and put it in a tub of water and look for bubbles. What a pain in the butt that is. An ultrasonic leak detector will not "hear" and airbag leak.

Does it make sense to make it a part of the installation procedure to test all new bags prior to installation, or is this a pretty rare occurence?

Seems like it would be a real pain to have to test every new air bag, but I guess it would give some sense of insurance that you don't have to do it twice (or more) times to achieve a leak-free installation.

As I have 6 replacements to go, I'm sure hoping that this is a very rare problem :(

I remember seeing a photo of a metal jig for inflating bags out of the bus. It was in the prevo factory service manual we got with ours. That I believe was designed for when the bags were different and the tops came separate as Jon mentioned.

In any event if you had such a jig and had new bags I do not think it would be too much extra time to air them up before putting them in.

Good Grief.

Paul,

Over the years I have installed 16 air bags on my buses and helped with a smilar number of installs. I was replacing them when the tops were separate and had to be seated using a cage which I built.

Until Eric and Deb found the leak in one of their new airbags I have not had a problem. The current air bag designs have done away with the removeable top and have a metal top that is rolled and crimped over the rubber. That is where Deb found the leak in a new air bag.

Since they are having the leans with the second new airbag, and they have replaced the 3 port Norgren, and isolated the problem to the new Norgren, the new tag axle air bag or the associated fittings it points to the air bag again. So to answer your question I think from now on I am planning on testing air bags before they are installed because it is time consuming to remove and replace them after they are installed, but more importantly, if they do leak you spend a lot of time ruling everything else out.

I used to bench test Norgrens before I installed them using a rig I made up of Home Depot valves and fittings and hoses. I am going to go back to doing that also.

Besides Roger, Deb and Eric, I know Brian and Jim Shoen have replaced air bags recently. I don't know if they have had any problems. This may just be a fluke.

Quote:

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Originally Posted by Joe Cannarozzi

So Eric, what happened with that bag and that leak. You cannot just leave us hanging.:rolleyes:

What about that bench test?

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Sorry, Joe. Did not mean to leave you hanging. Bench test results. After picked up Jon Wehrenberg's steel cage last night, tried it this morning. Used40 PSI in bag. Put under water in our utility sink. Could not get bubbles.

Jon used this "cage" to seat the bead on old style air bags. It was not built (or, in the ordianary Jon W. manner of operating, overbuilt) to handle the full pressures of an air bag. So in conversation this morning, he advised me not to inflate more than the 40 PSI without some additional structural steel in the cage to insure it could handle more PSI within the air bag. Before I ship the bags back to Prevost under warranty (since they've not seen one mile of service), we're going to strengthen Jon's steel cage so we can test at 100 PSI. We want to reproduce the leak we know is there with a bench test. Then we'll employ same method to test BAG NO. 3 before we intall it.

But with air bag number 2 of the new ones at the left rear tag (Deb wants to know if anyone feels sorry for us yet or if we're just preaching to the choir), and with Deb re-checking left tag bag for leaks again today and confirming leaks, we opted to swap out BAG NO. 2 for what is now the third bag in that location in the last month or two. I used one of the older bags which we removed when we put the six new ones in. Hope it holds. We'll buy another, but will bench test before installation. By the way, tooting my own horn regarding my install time, I did complete removal to completed install of the left tag bag between 1:42pm and 2:07pm (25 minutes). I know there is not another bag on the bus I could do in that short time, but this bag I did.

So we aired it up to see if we'd get the leans in about 24 hours like we have been. Deb gets under bus with her ultrasonic leak detector, and I'm sitting between tag and drive on outside of bus. We both hear huge air sound, different from any we've had to date. Traced sound to in front of drive wheel mud flap, and we think it's called ride height valve exhaust port (at least that's what I think it is until Jon tells me it's something else). It caused the leans in about 10 minutes.

So call to Jon about new leak. We "exercised" our valve, at his suggestion. Did the Level Low up, down, left, right, front, drive, over and over again. And then over and over again, because the leak was still there. And then over and over again, because the leak was still there. And then over and over again, because the leak was still there. And then it returned but smaller. And then it seemed to quit. We'll see in morning. Maybe the air bag will hold this time, but the ride height valve will be the culprit. Fingers crossed that both hold.

So that's the update.

eric and debbie faires
huntsville, TN

Thanks Eric.

No one feels sorry for you.:p We know what you are up to.

You need not put that much in those bags to bench test them. I am going to go out on a limb and say I would be suprised if you had to even get to 75 to get it to start leaking again. They will never see 100psi during normal operation.

That ride height valve will "leak" actually exhaust air by design and it sometimes takes a very long time to bleed off when it needs to, gradually tapering off until it stops.

I am confident you are aware of that and the leak there is more than I have described.

I was thinking about installing a suspension pressure gauge but not to monitor normal operation. I thought it would be good when in level-low to tell me when I had topped out at any one corner and would thus prevent unnecessarily overinflating the bag by staying on the trigger after the suspension runs out of travel. We are not auto-level but have the old manually opperated system.

Trucks often have suspension air gauges. An axle carrying 17000lb has around 60 to 65psi in the bags. With our drives on the bus at 20000lb it will be about 75psi

Eric,

I give you and Deb a LOT of credit for tackling this project. It must be extremely frustrating to do everting possible to do the job right (which I'm sure you are, given the work ethic of your mentor) and still have to repeat the performance.

Although it was no where close to the work that you are undertaking, I can understand to a small degree what you're going through. I once had to replace 3 BRAND NEW thermostats that I was installing because it was the "right thing to do" while replacing radiator hoses on one of my cars. As hard as it was for me to believe, 2 out of the 3 new thermostats were defective. It was fun taking things apart the first time, but by round 3, well, my vocabulary had changed a bit.

Good luck in getting this job completed once and for all. I'm rootin' for ya !

Quote:

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Originally Posted by phorner

Eric,
Good luck in getting this job completed once and for all. I'm rootin' for ya !

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Even though Joe doesn't feel sorry for us, we're glad you're rootin' for us.

As of 6:10am today, it was leaning a bit but not much. Ride height exhaust was leaking, but slightly.

Deb will check my fittings on tag air bag install later this morning, and we'll take bus for a ride to see if that form of "exercise" improves our leans by perhaps blowing crud out of or through system. Fingers crossed.

Thanks, all.

eric faires
huntsville, TN

A footnote to all of Eric and Deb's problems. The original problem appears to be two leaky brand new air bags in a row. The old, presumably leak free air bag now installed will prove that as soon as this new problem can be corrected.

Just so everybody has the mental picture required, when the key (on almost all of our coaches) is "off" the air in all air bags should be locked in place by a five port valve that goes to its normally closed position. When the key is on, if the leveling switch is set to the road or driving position the path through that five port valve to the air bags goes through the ride height valve. In Eric and Debs case they have the bus fully raised so it is easier to work under the bus, and that ride height valve arm is in the position to exhaust air. Ordinarily it would not exhaust air with the key off, but in this case it appears the five port valve has decided to not fully close and is letting air pass through to the ride height valve which is exhausting air trying to get the bus to go down to the normal ride height. If the support stands were removed I suspect the bus would drop on that side until it reaches the normal ride height, at which point the ride height valve will stop exhausing air.

I know how much of a PITA this problem is by having worked for weeks to make my previous coach leak free. I also know how obsessive an owner can be when they realize how close they are to perfection and want to make that last little leak go away.

Here's the really scary part in all of this. Imagine if you will that this was happening on your bus. And unlike Deb and Eric you had no choice but to bring your bus to Prevost for air bag replacement. A slow leak in a new air bag would not show up as the leans for 12 to 24 hours. By then the bus is home leaning over in your driveway. So back you go, and if the techs do not fully understand the system some serious dollars will be spent by you until you either give up, or the problem is isolated and repaired. Doesn't that give you a warm toasty feeling?

Eric, if I am correct you are now testing your system relying on the fact that a previously good air bag when re installed will be leak free.
There is however the possibility that in the removal, and re install process that something happened to that bag and it will leak. Of course you have already gone through the process, so you might as well follow through. If the bus stays put you succeeded.

I think a better way to test the original air bag in a speedier fashion (less time waiting for parts, and less remove and replace), could have been the instalation of a cap on the end of the line feeding the suspect airbag, thus isolating it from the system and proving that anything beyond the cap is at fault for whatever reason.

Jim,

That has been done, albeit in a different fashion.

By using the tag axle lift feature the drive axle air bags are isolated from the tag axle air bags via the three port Norgren.

Eric and Deb have done that and thus can rule out anything forward of the three port Norgren as being a potential leak. At least up until the apparent problem with the five port Norgren.

In both instances Deb found leaks at the top crimp on the tag axle air bags. She is incredibly fortunate in that the leaks showed up where she could see them blowing bubbles. The odds of that on an installed air bag are 50/50 because unless you start pulling wheels or fender liners at best you can only see 1/2 of the air bag.

Although you may not be aware Hector is going to provide a design for a bubbler device as soon as he gets his barn building project under control. Using Hector's device will allow exactly what you describe by making the bubbler in essence the cap and being able to see if anything downstream from the bubbler has a leak even as minute as a bubble. There are 5 or 6 different type fittings on all our suspension, so with the bubbler and five or six adapters, starting at the origin, a person could methodically work through an entire coach testing each and every component until the entire system is bubble free.

Patiently waiting on the sidelines ;) for the outcome

Here is the latest. NO LEANS after tag bag was replaced by 3rd new one from Prevost. This means that 2 out of 8 they sent to us had leaks. 25%. We will be testing any and all bags in the future prior to installation. Related to that, using a metal jig that was only safe to pressure up to 40 psi, both defective bags (which produced a very characteristic bubble pattern when installed on the bus) showed NO signs of bubbles under water. This means, that they must be tested under higher pressure than 40psi, and we don't know what that magic number is because we have to ship the bad bags back to prevost before we leave for our trip next week. We will work on a suitable design for a metal jig that can be used to test bags off the bus, but we are not experts in this area. If someone has some ideas, please share.

Now, to update the big strange 2nd noise we heard Sunday, in front of the mud flap on the drivers side, just in front of drive tire... We believe it to be ride height valve exhaust tube. At Jon's suggestion, we "exercised" the level low/drive valve by switching it back and forth numerous times and adding and removing air. Each time we did this, leak got smaller and smaller, until it finally stopped. So, I assumed that leak there was indeed related to some crud that must have gotten stuck in the 5 port. Then, it came back after the next test drive when we put it in level low, but not to the degree of the first time. For some unexplained reason, it seems to stop if you raise and lower the tag axle. I don't know what relationship there is between these. I really didn't think they were related. It may just be coincidence, but 2 times this has worked now. I'm going to call Prevost service to see if they have any ideas. Anyone out there want to guess?

But for now, we are feeling better. I have learned so much from this POG forum and from Jon and Hector. Thank you all!!!!!

BTW, Prevost parts man told me Sunday when we ordered our 3rd new bag for the tag, that he had "never heard of a leak happening from the place where I was describing." I assured him I had seen it with bubbles and heard it with my ears and it was leaking. He did not sound like he believed me. It was unbelievable to me we could have gotten 2 bad bags in a row, but now I am proven right. Yes, it does feel good! :) I think I have mastered the bubble technique in the process, and I am highly skilled with my ultrasonic leak detector and electronic stethoscope as well. I'll happily pass my new knowledge to anyone in need.

What Eric and Deb did not point out is that as a result of the air bag leaks they got real good at removing and replacing the tag axle air bag on their coach.

I was told the replacement of the third one took 24 minutes.

That is impressive.

Well this one is really distressing.

When Deb and Eric found the new bag leaking (twice) it was at that crimp where the bag meets that top plate, a mechanical failure of sorts.

The one I have been handed has small pinholes all over it, and it was HELL to even find them. Initially I literally triple checked them after instalation and got up this morning and the left rear was COMPLETLY deflated. So under I went again going through 2 bottles of the soapy goo and found NOTHING. Even put in another 3 port norgren, it was the last original component back there. Went out in the darkness to check again after 5 hrs. and nuts the thing is going down again. Everything has been replaced 5 and 3 port norgren, ride height valve and 3 new bags.

Up until now when checking new bags I would spray that top ring and around the bottom bell. Well this piece of crap is perforated ALL over it. I think If I did not go and look in the darkness with a flashlight I would not have seen it.

If I got up in the morn and found it down again I had it in mind to rig up a line so I could hook to each bag one at a time and check them independently.

Looks like I am now gonna make up a gadget to do just that and now these darn things are ALL gonna have to be bench tested.

Beautiful, many have decided to spend the extra time and money and pull everything when doing this job and it looks like Zimbabwe could produce better parts.

Well Mr. Goodyear thank you for the great quality control.

Since all air bags have the same size pipe threads a T fitting threaded into the bag, with a Schrader valve and very sensitive pressure gauge on the other two legs of the T would be all that is needed.

However............I am not convinced a low pressure test will reveal all the leaks.

Many moons ago when the air bags had tops that snapped in I built a cage so they could be inflated to snap in the tops. I still have the cage, and if it were properly reinforced it could be used to contain the air bag while the air bag were inflated to the maximum pressure (around 100 to 110 PSI).

But that would involve 8 days of testing (one bag per day) to find the most minute leaks on all 8 air bags required for a coach.

Or, and here is a wild idea, maybe, just maybe Prevost could be expected to improve their QC or get a different supplier who can make air bags that do not leak.

What a clever idea, the one about getting better parts.

I don't think it would take a whole day to see. Heck as soon as you see any loss in pressure at all your done, its JUNK.

Maybe Mr. Goodyear could provide us with the test cages since they now seem to be necessary. Someone could get seriously hurt testing with a home made cage that wasn't strong enough.

I'm thinking basic shop press could be used with some simple additions.

Quote:

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Originally Posted by Joe Cannarozzi

What a clever idea, the one about getting better parts.

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Is there another manufacturer of identical, but possibly leak free, bag? I think I have heard that Firestone makes bags. Anyone else? Would they possibly be direct replacements?

Joe, we feel your pain dealing with leaky air bags that should not be leaking.

eric and debbie faires
huntsville, TN

When I shopped the bags on line I got the trade number for them from Prevost. Air bags are apparently generic. My first problem was nobody carried those air bags. Apparently Prevost either has something unique about them, or it is a relatively rare number. My bus has two different numbers. Some use all the same air bags.

Making matters worse, nobody came close to Prevost on air bag prices, especially after I negotiated a quantity discount of almost $20.00 per air bag. The closest I could come from anybody was about $60 more per air bag.

So the bottom line is unless and until Prevost gets enough warranty claims due to defective air bags they will not be changing suppliers. This is especially true if the air bags used on new buses are a different part number than the one we use on our older coaches. The can't get real excited about crappy air bags because they have no labot invested. But if the air bags used on new coaches are experiencing similar quality issues, and their warranty costs go out of site because a mechanic is spending a day or two per bus to sort out bad air bags the fit will hit the shan.

Quote:

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Originally Posted by hobobimmer

Is there another manufacturer of identical, but possibly leak free, bag? I think I have heard that Firestone makes bags. Anyone else? Would they possibly be direct replacements?

Joe, we feel your pain dealing with leaky air bags that should not be leaking.

eric and debbie faires
huntsville, TN

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eric,

I have Firestone air bags on my coach and (knock on aluminum) I haven't had any leaks. My previous coach was 13 years old when I sold it; no leaks.
It might be worth a phone call!

Tuga,

Eric and Deb have leak free bags on their coach now. The issue is not that Firestone is necessarily better than Goodyear or BF Goodrich, but knowing when the bags are installed they don't leak is the most critical thing for anyone who does replace their air bags.

We change air bags because we have the leans or because the air bags have aged out and are starting to dry rot. The expectation is whatever air bags we get will be leak free.

We have zero ability to determine who makes the best air bags. There are folks who have had BF Goodrich on their coach for 15 to 18 years and they still don't lean. But like Joe and Debbie can attest they have brand new ones that do leak. Prevost installs thousands of these annually and they like other OEM companies can prove via data collected by their QC departments whose air bags have been the most trouble free, but they are not about to share that info with us or anyone else.

I don't think Newell even produces coaches in sufficient quantities to be able to state authoritatively who makes the "best" air bag. Consumer reports does not have a test program for them.

The 2 replacement air bags for the 2 leakers came the day before yesterday I installed them yesterday I got up this morning and they are both showing bubbles around that top crimp.

Good Grief

Just for some #'s I have installed 3 sets this summer and adding the replacements its 26 bags total and 4 were no good.

Joe, from now on your going to be BAG MAN. What do you think? Is that OK?

:DJIM

Elgin is sending me 2 more from a different inventory stock, in Florida. They are contacting their purchasing agent to make him aware of the situation.

I called and spoke to a Jim who is the parts manager in Nashville and he has not heard of any problems before this.

If these two they send me tomorrow show bubbles I will not request any more until something is done to my satisfaction.

Respectfully, The Bag Man-Chicago Cartel

I think it is a bad batch. Jon did both his buses and Rodgers and I did Loydes and Warrens without incident. Then Erik comes up with 2 bad ones and I find 4 and all in short order.

If Nashville says they never had problems, perhaps Debbie should go down there and hit the guy up side the head. If I recall the conversation with Deb that was the same fertilizer he told her.

Well boys and girls this CC I am currently working on has really been a lesson in perseverance.

I had to pull a bran new 3-port norgren I installed and replace it with another bran new 3-port cause, guess what, it was a leaker:eek:

Then after I got it in and switched the level low back to road mode, it wouldn't. The particular coil that operates that solenoid in the steer bay decided to quit, switched 2 around to verify that. All the while Tully the owner was in route to pick it up:eek:


Sheesh

He was very understanding and agreed that it is better the thing failed here and not out on the shoulder of I-65.

I received the CATALOG of papers and questions that have to be completed to return new defective parts that have been installed back to Prevo.

Orren sent me a PM wanting the skew off of the bags so he could cross them to Firestone so he can start stocking them.

If he can get them at similar cost I have ordered my last suspension component from Prevo.

He also mentioned switching to Firestone because of problems with Goodyear, he is currently traveling and did not elaborate.

The ride heights, Norgrens, air driers and shocks I'm sure he can do.

Your doing a great job Joe!