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Air suspension dynamics/anatomy?

I am still sleuthing around trying to diagnose my leaking/non-maintenance of level while parked.  A couple of weeks ago we replaced all airbags and the next morning everything had settled so there was no air suspension of any sort.  Today I aired up the tanks, raised the beast up enough to get the 8 safety blocks out of position, used the HWH control panel to achieve level and left the air at full. An hour later I am at about 95 psi on both tanks.  When I checked the airbags now (they have had no apparent air pressure in them while the blocks were supporting the body off the running chassis). the air bags at the rear wheels are at different heights. The ones forward of the wheels are about an inch lower than the ones aft of the wheels.  This leads to the question; why are there two bags at each wheel?  I had assumed that two are better than one since they could share the load and one was available as a 'back-up' for the other.  I haven't found anything in the Forum regarding the 'anatomy' of the air suspension system that would suggest that they are each controlled by a separate solenoid.  Am I wrong? (P.S., replacement o-rings are on their way to me from MOT so that I/we can replace them, in case they are the source of a leak.
Woody & Sandy Lloyd
1993 Grand Villa
Unihome U280
Cummins / Allison
Build # 4379

Re: Air suspension dynamics/anatomy?

Reply #1 –
No expert here but almost sounds like some of your check valves may be leaking back.
96 U270 BUILD 4810
85 380SL
Drummonds TN.

Re: Air suspension dynamics/anatomy?

Reply #2 –
Quote from: Mike_Sandra_Lloyd –
Why are there two bags at each wheel?  I haven't found anything in the Forum regarding the 'anatomy' of the air suspension system that would suggest that they are each controlled by a separate solenoid.  Am I wrong?
Woody,

If you wish to understand how the HWH leveling system interacts with the Foretravel air bag suspension, I once again urge you to read/study the HWH tech manuals linked below.  They present a clear and concise explanation of how the two systems operate, including exactly how the air bags are controlled by the solenoids on the 6-pack manifolds.  They will, I am sure, answer many (if not all) of your questions. 

http://www.hwhcorp.com/ml20635.pdf

http://www.hwhcorp.com/ml11148.pdf
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Air suspension dynamics/anatomy?

Reply #3 –
Thanks Chuck. I have downloaded the manuals and I meant to thank you earlier about providing those links. They are very useful. You are right they do answer a lot of questions and I am working on determining solutions.  My question about why one, (the forward one vs, the aft one) of a set of two bags per wheel would be unpressurized. I can see from the air schematics that each bag has its own line from the manifold. Assuming that the 'leak' is the fault of o-rings in the solenoid, it remains odd that both the forward airbags of the rear wheels should be soft at the same time while the rear airbags of the rear wheels are both pressurized. My assumption has been that the airbags on any given wheel should be acting in tandem, not independently - thus my question about the anatomy of the system.
The solenoids affect the left and right raising and lowering functions.  Assuming that the signal is to 'raise' the left rear (for example), it would make sense that both airbags of that wheel would work together to achieve that task. If that is not happening then I wonder why not? I haven't found the answer to that is either the HWH Textbook nor the Service Manual, but I will keep looking.
Thanks again, Chuck for your recommendations on these two important publications from HWH!
Woody & Sandy Lloyd
1993 Grand Villa
Unihome U280
Cummins / Allison
Build # 4379

Re: Air suspension dynamics/anatomy?

Reply #4 –
Woody,
After reading your troubles it seems like you may have multiple air lines that have been installed in the wrong ports on your rear six pack. Have you traced the lines from each air bag back to the rear six pack manifold to make sure that they are installed on the right port?

Pamela & Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Air suspension dynamics/anatomy?

Reply #5 –
Quote from: Mike_Sandra_Lloyd –
The solenoids affect the left and right raising and lowering functions.  Assuming that the signal is to 'raise' the left rear (for example), it would make sense that both airbags of that wheel would work together to achieve that task. If that is not happening then I wonder why not? I haven't found the answer to that is either the HWH Textbook nor the Service Manual, but I will keep looking.
As I understand it, your problem is this: both air bags on the same corner are not working in tandem.  I.E. one bag has more or less pressure than the other bag on that corner.

Here is my (totally nonprofessional) analysis of this problem:

As you noted, at each corner of the coach, each air bag does have it's own air line.  But, both of these lines are fed from a common manifold in the 6-pack.  In each 6-pack, there is one common manifold for each side of the coach.  The air pressure in each common manifold is regulated by 3 solenoids: travel, raise and lower.  Only one solenoid (for each side of the 6-pack) can be open at a time.  If you are in "Travel" mode, then the travel solenoid for each side is open.  When you are not in "Travel" mode, the travel solenoid is closed, and the other two solenoids (on that side) can be activated by the leveling system.

The HWH leveling system cannot control a single individual corner of the coach - it can only work with "pairs" of corners.  For instance. it can raise or lower the front of the coach.  To do this, it will add air or release air from both front corners of the coach.  Or, it can raise or lower the right side of the coach.  To do this, it will add or release air from both the right front corner, and the right rear corner.  It cannot, however, raise or lower just the right front corner of the coach.  (The exception to this is when in "Travel" mode, at the rear of the coach, each corner has a separate height control valve and therefore can adjust itself up and down independent of the other corner.)

Example: To raise the front of the coach, two different solenoids on the front 6-pack must open simultaneously: the left side "raise" solenoid, and the right side "raise" solenoid.  IF they both open at the same time, the front of the coach will come up.  If one solenoid fails to open, then on that side the 2 air bags will not be pressurized, and that corner not come up.  But even in this situation (malfunctioning raise solenoid) both air bags on the same corner would still be at the same pressure.

I can only think of 2 ways in which the two bags at any corner could be at different pressures.  First, a leak in one bag, or a leak in the air hose or air hose connections serving that bag.  Second, a blockage of some kind in the internal 6-pack manifold serving one of the bags, or in the air hose going to that bag.

The opinions above are deduced from reading the two manuals linked earlier in this thread.  If any member finds a flaw in my logic, please feel free to point it out.  I'm still trying to figure out and learn this stuff, just like everyone else.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Air suspension dynamics/anatomy?

Reply #6 –
Since we have the same air pressure in both airbags on a given corner and the same weight on both air bags, then if one bag stands taller than the other could there be some binding in one or some of the suspension movable points or shock absorber on that corner?
John Duld
1995 U320C SE 40'

Re: Air suspension dynamics/anatomy?

Reply #7 –
Quote from: John Duld –
then if one bag stands taller than the other could there be some binding in one or some of the suspension movable points or shock absorber on that corner?

John,
Yes you could have a stuck bushing bolt in a torque tube/trailing arm.
Yes you could have a shock broke but not likely.
You can have a different height on the 2 air bags due to the arc/travel on your torque tubes.

Pamela & Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Air suspension dynamics/anatomy?

Reply #8 –
Blockage or a leak from a stuck open valve. Can be caused by the all mighty >:D  MUD DUBBER. 
1994 U280
Build #4451
"If everyone is thinking alike, then somebody isn't thinking"

Re: Air suspension dynamics/anatomy?

Reply #9 –
The control arms swing from the front. The shorter distance of the front bags to the pivot require a shorter  bag then the longer traveling rear bag.  IMHO.

Re: Air suspension dynamics/anatomy?

Reply #10 –
Thanks all for the input.  Chuck - I now understand the dynamics of the HWH lifting system with signals going to all airbags on a side or all airbags on the front or rear.  Yesterday, during my testing of the system, it seemed to be working to TRY to complete some leveling (left side was low, as well as having only one airbag on each rear wheel with any pressure in it.  After several tries the system was 'calling' to be shut off because I saw that the 'Excess Slope' light had come on. It (smart system that this is) was admitting defeat! However I felt good that the HWH electronics seemed to be functioning as it should, leading me to the conclusion that my issue was more of a 'plumbing' issues one than a control one.  [While I am at it, I want to ask if anyone knows where the Control Box is on a U280?  I have traced the modular wire towards the back but have not been able to see it in my looking in cargo holds or in my slithering underneath the beast.]

The airbags are all new (and therefore not likely to be leaking, especially the airbag on each orientation on each side having a defective leak simultaneously), and replaced a couple of weeks ago but not yet used in travel. I am narrowing the leak search to the connections (and perhaps a t-joint that leads to each 'foward' or 'aft' bag pair at the rear six-pack.
 I have soap-mixture sprayed all the connections (except those at the manifold) and that obviously needs to be done now. I drove it about 50' now (trying to limp 40 miles into town to see the mechanic) and stopped to check.  I had been hoping that the 'Travel' setting/solenoids would assist, and/or change the situation but there was not consistent 'travel height' among the airbags.  One rear side had only a 'finger-width' clearance, so obviously not enough for driving with (one airbag on each side at the rear was still unpressurized). So my mechanic makes 'house-calls' and is on his way out.
Thanks again, Chuck, for your detailed confirmation of how the HWH system works.
Woody & Sandy Lloyd
1993 Grand Villa
Unihome U280
Cummins / Allison
Build # 4379

Re: Air suspension dynamics/anatomy?

Reply #11 –
Quote from: Mike_Sandra_Lloyd –
I drove it about 50' now (trying to limp 40 miles into town to see the mechanic) and stopped to check.  I had been hoping that the 'Travel' setting/solenoids would assist, and/or change the situation but there was not consistent 'travel height' among the airbags.  One rear side had only a 'finger-width' clearance, so obviously not enough for driving with (one airbag on each side at the rear was still unpressurized). So my mechanic makes 'house-calls' and is on his way out.
Good decision to not drive. With only one air bag lifting on a side, this is putting a lot of stress on the suspension framework, especially the rear suspension which carries the majority of the coach weight.
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: Air suspension dynamics/anatomy?

Reply #12 –
Quote from: Mike_Sandra_Lloyd –
While I am at it, I want to ask if anyone knows where the Control Box is on a U280?  I have traced the modular wire towards the back but have not been able to see it in my looking in cargo holds or in my slithering underneath the beast.
Look in the front storage bay, driver side, on the forward wall, next to the generator cooling duct.  Silver aluminum box.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Air suspension dynamics/anatomy?

Reply #13 –
There is no need to stumble around trying to guess what is wrong with your system.  The HWH 600 Series Service Manual (2nd link in Reply #2) includes a very clear and concise series of trouble shooting steps.  It will allow you to ascertain exactly what function/component is not operating correctly.  Start on the first page, read the instructions, follow the steps...EASY!
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Air suspension dynamics/anatomy?

Reply #14 –
Okay - we are most of the way there! When the mechanic was doing some experimental problem solving of the total air leak (the day after replacing all airbags) he disconnected some hoses then connected two back in the wrong place.  When he came back and we used the air schematic (http://www.hwhcorp.com/ml20635.pdf  - http://www.hwhcorp.com/ml11148.pdf) and traced the lines back to the 'six-pack' he found that he had mixed left and right 'raise' hoses and that confused the system enough to make it dysfunctional. So that fix was belated but relatively easy (once all the other possibilities [inoperative electronics in the control box or control panel] were discounted - it could only be a 'plumbing' problem.

Thank you all for your input!

I suspect that the next order of things will be to overhaul the solenoids of the six-packs, just to further ensure that the system will work as designed when we want it to.  It has been a good learning experience (even though the learning curve has felt steep at times)!
Woody & Sandy Lloyd
1993 Grand Villa
Unihome U280
Cummins / Allison
Build # 4379
 

Re: Air suspension dynamics/anatomy?

Reply #15 –
Good news, and good troubleshooting.

Thanks for the update.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020