01-17-2018, 08:02 AM
Gurus,
This post is a continuation of my airbag woes. We have made progress, but there is no victory dance yet. Thanks to Richard Entrekin we are much, much closer to finding a solution.
Problem: The coach will sometimes keep air in its airbags with the key off, and sometimes it will just leak out suddenly, or it may leak dow more gradually. Normally it is the right rear where this happens. I have fairly new six pack solenoids and brand new Height Control Valves (HCVs). The problem has been with me since I bought the coach (from Newell) six years ago. The airbag has been replaced multiple times. I can reproduce the problem at will by airing up the coach and then letting air out of the bags. Fully inflated, it stays inflated. Partially inflated, it leaks down to nothing.
Investigation: When I pulled into Richard's driveway, and shut down the engine....The right rear airbag started venting like crazy. I went from normal ride height to being on the skids in a matter of 10-20 seconds. Remember that the air in the bag is augmented by a fairly large auxiliary air tank mounted in the frame. This was by far the most dramatic manifestation of the problem to date. And the coach did it RIGHT IN FRONT of RICHARD! Wow! I thought that I had somehow ruptured the airbag.
The first step was to chock and block the coach. Richard pulled out a pair of the biggest jack stands I have ever seen. We raised the coach and placed the stands. In addition we put cribbing under the trailer hitch. We did my process of being aired all the way up and then letting air out of the bags. Richard was able to pinpoint the leak as coming from under the airbag. (Where the metal is)....NOT THE RUBBER PART!
We decided to remove the offending airbag (aft drive axle - passenger side). After a few vocabulary expanding minutes, Richard had the bag out.
Inspection of the bag yielded an surprising observation...The support ring is not attached to the bag by anything other than friction.
We decided to test the bag out of the coach. Richard rigged up a series of air fittings that allowed us to air up the bag to 20lbs (with proper safety procedures). The bag did not leak - at all!
Along the way we realized that the "piston" part of the airbag was also not glued but rather worked like the bead on a tire. Air pressure from inside the bag keeps the piston air tight against a bead that is built into the rubber "bladder".
At this point we turned our attention to the coach and noticed that the platform that the airbag sits on was slightly warped around the edges and is not absolutely flat. Hmmmm.
Here is the theory that we came up with. The bag works like a tire...it seals against the piston. To guide the bag and to keep pressure when it is deflated, the "ring" is used. In my case we think that the ring is shorter than the piston (caused by the pancake shape of the platform) which means that the piston bottoms out on the platform. This allows air to escape around the piston.
Lets look at some pictures....
This is the normal configuration of the airbag.
The air inside the bag presses the the piston down and the ring essentially presses up. The edge of the bladder is pinched between the ring and the piston edge.
If you are still reading....hang on...it gets interesting from here on out.
Richard installed the airbag back into the coach along with the air fitting that allowed us to fill the bag WITHOUT THE RING. He put the bolts back into the bag and let the weight of the coach down. Richard got out from under the coach. We then gradually added air to the bag. Around 20-30 lbs.....the bag went "POP" and coach dropped. The piston had pulled away from the "bead" and had let all the air out of the bag.
This makes sense. While the bag will hold air just fine, the platform is exerting pressure to push the piston into the bag. As the top of the bag is lifting the coach the bottom is applying pressure to the piston. At around 25lbs or so, the pressure was too much.
From this we figure out that the ring is designed to apply pressure around the edge of the bag and to keep the pressure off of the piston.
Our theory is shown in the figure below...
The piston is just about the same size as the ring. But, since the platform has a curvature, the ring is bottoming out and not allowing the ring to do its job. Under some circumstances like the bag being partially inflated, air can get around the piston as in the previous picture.
So, Richard welded on a couple of pieces of sheet metal to raise the ring and keep the piston from bottoming out.
After the installation of the spacing rings, the coach held up with no loss of air for five days. (No leaks at all!!!)
But....here is the sad part. When I returned home and parked the coach, it leaked down overnight.
At this point, I am not sure is our theory is wrong or the rings were not tall enough. We now know much more about how the airbag works, and will collect and present more data as it becomes available.
This was a super-fun learning experience. Stay tuned for more information.
Bill
This post is a continuation of my airbag woes. We have made progress, but there is no victory dance yet. Thanks to Richard Entrekin we are much, much closer to finding a solution.
Problem: The coach will sometimes keep air in its airbags with the key off, and sometimes it will just leak out suddenly, or it may leak dow more gradually. Normally it is the right rear where this happens. I have fairly new six pack solenoids and brand new Height Control Valves (HCVs). The problem has been with me since I bought the coach (from Newell) six years ago. The airbag has been replaced multiple times. I can reproduce the problem at will by airing up the coach and then letting air out of the bags. Fully inflated, it stays inflated. Partially inflated, it leaks down to nothing.
Investigation: When I pulled into Richard's driveway, and shut down the engine....The right rear airbag started venting like crazy. I went from normal ride height to being on the skids in a matter of 10-20 seconds. Remember that the air in the bag is augmented by a fairly large auxiliary air tank mounted in the frame. This was by far the most dramatic manifestation of the problem to date. And the coach did it RIGHT IN FRONT of RICHARD! Wow! I thought that I had somehow ruptured the airbag.
The first step was to chock and block the coach. Richard pulled out a pair of the biggest jack stands I have ever seen. We raised the coach and placed the stands. In addition we put cribbing under the trailer hitch. We did my process of being aired all the way up and then letting air out of the bags. Richard was able to pinpoint the leak as coming from under the airbag. (Where the metal is)....NOT THE RUBBER PART!
We decided to remove the offending airbag (aft drive axle - passenger side). After a few vocabulary expanding minutes, Richard had the bag out.
Inspection of the bag yielded an surprising observation...The support ring is not attached to the bag by anything other than friction.
We decided to test the bag out of the coach. Richard rigged up a series of air fittings that allowed us to air up the bag to 20lbs (with proper safety procedures). The bag did not leak - at all!
Along the way we realized that the "piston" part of the airbag was also not glued but rather worked like the bead on a tire. Air pressure from inside the bag keeps the piston air tight against a bead that is built into the rubber "bladder".
At this point we turned our attention to the coach and noticed that the platform that the airbag sits on was slightly warped around the edges and is not absolutely flat. Hmmmm.
Here is the theory that we came up with. The bag works like a tire...it seals against the piston. To guide the bag and to keep pressure when it is deflated, the "ring" is used. In my case we think that the ring is shorter than the piston (caused by the pancake shape of the platform) which means that the piston bottoms out on the platform. This allows air to escape around the piston.
Lets look at some pictures....
This is the normal configuration of the airbag.
The air inside the bag presses the the piston down and the ring essentially presses up. The edge of the bladder is pinched between the ring and the piston edge.
If you are still reading....hang on...it gets interesting from here on out.
Richard installed the airbag back into the coach along with the air fitting that allowed us to fill the bag WITHOUT THE RING. He put the bolts back into the bag and let the weight of the coach down. Richard got out from under the coach. We then gradually added air to the bag. Around 20-30 lbs.....the bag went "POP" and coach dropped. The piston had pulled away from the "bead" and had let all the air out of the bag.
This makes sense. While the bag will hold air just fine, the platform is exerting pressure to push the piston into the bag. As the top of the bag is lifting the coach the bottom is applying pressure to the piston. At around 25lbs or so, the pressure was too much.
From this we figure out that the ring is designed to apply pressure around the edge of the bag and to keep the pressure off of the piston.
Our theory is shown in the figure below...
The piston is just about the same size as the ring. But, since the platform has a curvature, the ring is bottoming out and not allowing the ring to do its job. Under some circumstances like the bag being partially inflated, air can get around the piston as in the previous picture.
So, Richard welded on a couple of pieces of sheet metal to raise the ring and keep the piston from bottoming out.
After the installation of the spacing rings, the coach held up with no loss of air for five days. (No leaks at all!!!)
But....here is the sad part. When I returned home and parked the coach, it leaked down overnight.
At this point, I am not sure is our theory is wrong or the rings were not tall enough. We now know much more about how the airbag works, and will collect and present more data as it becomes available.
This was a super-fun learning experience. Stay tuned for more information.
Bill
Bill Johnson
Birmingham, Alabama