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Old 05-31-2016, 01:43 PM   #11
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Originally Posted by Brad_SwiftFur View Post
I have driven quite a few air-ride trucks over the years. The air suspension on my Volvo "airs up" at around 80 (as does the cab) ... and after shut down, it can be heard adjusting itself for several minutes. The air system on that truck has leaks, it will go down to almost nothing overnight. The compressor works well, so we haven't bothered to diagnose it and with nearly 770K miles it isn't likely to be in the fleet much longer.

I'd say your air suspension is "normal behavior", but if you wanted to try to eliminate the leak, my first suspect would be the "leveling valve" as this is a common failure item.
im also beginning to think the levelling valve.. I sprayed down the air bags all around and dont get any air bubbles.. now I have not disconnected one yet and pressure tested them with shop air to trukly know...

the air valve seems to constantly hunt though.. making me think that when it shuts off the supply air it automatically goes to exhaust mode with nothing in between so its alsways going up and down slightly..

my bus has a brand new air compressor and only takes a couple minutes to air up to over 90 so its not a pressing deal.. but just an annoyance more than anything. ..



-Christopher
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Old 05-31-2016, 05:55 PM   #12
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I have debated trying to install air suspension but after many times trying to find what I want? I will stick with what I have?
Cadillac for an idea if that valve is a problem? Why not add a PRV and guage for each bag with check valves for each?
I know I am trying to stay with the original design to keep the house seperate from the bus hitting the road.
For me adding air bags for suspension meant I wanted that system seperated buy valves and prv's and check valves and gauges for each.
Now I want to deal with my spring suspension and add some air powered feet/jacks/legs at all four suspension point to controll the rock roll effect when parked for a while.
Therefore zone controll of each without questioning which one?
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Old 05-31-2016, 06:24 PM   #13
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I cant really install a PRV on each bag as the automatic height adjuster valve handles adding air to the bags... it appears both bags are one circuit..

what I could do is put a solenoid valve right after the regulator valve on the tank that the suspension is connected to.. then I could turn the suspension on or off eithe on my console or automatically with the key...

sure it might use some air when I first start, to pump it up, however it wouldnt use all my air down to 60 PSI...

its really just an annoyance since the suspension does work.. the bags hold air and the bus adjusts properly.. might be best to just say that the time involved waiting for my air alarm to shut off is good letting the engine idle and warm up a couple minutes...

I *AM* going to put a switch on those blasted air shutters though!!.. the darned thinbgs closed up on my today and ran my temp gauge up north of 210 before they re-opened..

its 90 out the shutters never need to close..

-Christopher
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Old 05-31-2016, 07:01 PM   #14
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I was saying if the automatic adjuster valve is a problem Then make up your own manual adjuster valve ID station and put the air where it is needed? Like a test station? Much less effort and thought than troubleshooting a bad TXV valve?
Kiss method?
You are good in the HVAC stuff.
I have installed many a VRF system with the same (in thought ) problems you are having with your air suspension? Not leaks
The engineers saying what you have can't do that and the factory tech saying well it is (you can probably relate) if your diverter/unloader valve is bad? Then I would probably build my own?
In a compressed air world?
Looks my dash board or somewhere has a lot of gauges? Talked myself into it.
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Old 05-31-2016, 07:23 PM   #15
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my way more is to figure out if the behaviour is normal.. then if its not to rteplace the bad auto valve if it is in fact leaking air into the bags causing the system to think its raised too high and exhaust air.. an "internal leak" of sorts..

yeah like a TxV that decides its not going to reduce the flow and saturates the evaporator with liquid... been there before more than once...

or the thermal bulb gas leaks out... valve goes to its minimum... Most techs would punch a bunch of freon in.... you or I would probably stick a bunch of temp probes on first to try and figure out what its doing...

clear site glass, low head, low suction... fools a lot of techs out there..



I like dashboards full of gauges.. I'll be adding a few as.. like you..I want to know whats going on inside of things... lots can be learned when you learn the "normal" of your gauges.. and then see one go out of whack.. gives you often a heads up...

-Christopher
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Old 05-31-2016, 11:05 PM   #16
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Out of all the trucks I have driven, only a couple had gauges for air suspension pressure. The primary reason for these is so drivers can get an idea of how heavily loaded the truck is. With some experience, a driver can get a reasonably close estimate if he will be overweight (either by gross weight, or by axle weights/weight distribution). While you *could* add such a system to a bus (and many builders likely offer it as a factory option), I personally see little need for it, no more weight than most of us carry.

Leveling valves aren't all that expensive, and not all that hard to install. 2-3 bolts, a couple air lines, and the linkage is usually all that's involved. Air bags are pretty tough, for all the abuse they take, they have to be. I've seen 'em fail, but slow leaks are fairly rare.

My own personal experience as to air systems losing air pressure - Suspension leveling valves. Number one failure rate on the trucks I have driven. 7 years with one company, 2 Volvos, 3 valves replaced. Previous company, 60+ air ride trailers, we replaced 2-3 valves a month (of course the trailers were showing some age and heavy use).
Number 2 on this list - Air dryer. 2 replaced so far. They can be rebuilt, but at $95/hour for labor, it comes out cheaper to replace the whole thing. My truck uses an oddball dryer, but many trucks and buses use a "universal" one. Typical symptom of air dryer failure is a constant hissing of air pressure, and air system may not build up past 60 PSI (or sometimes not at all) ... a partial failure can have the system leaking quickly at idle but a strong compressor can keep up at higher RPM's. Some dryers have a serviceable filter which should be done periodically.
Number 3 would be "everything else". Air compressors can fail (and occasionally do), air bags deteriorate with age, tank purge valves can gum up and stick, plastic air lines can get brittle, rubber seals degrade ... all the usual stuff.
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Old 06-01-2016, 12:59 AM   #17
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You're making this way more complicated than it needs to be... the air is going somewhere. Air it up til it purges, shut the engine off and go see what the air is coming out of. If it is an air bag, replace it. If it is a valve, make sure no other valve could cause it to leak. If not, replace it. What kind of bus is it? Air ride systems are pretty simple, seriously. You don't need to use shop air for anything. Just need soapy water, your ears and feel for a breeze coming out of something it shouldn't.
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Old 06-01-2016, 01:37 AM   #18
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I had one truck that just due to age and the fact that EVERYTHING was air-actuated and it would purge every last pound of air while it sat overnight. The suspension would be sitting on the stops and it'd have to run for about ten minutes just to build up the air pressure for all the bells and whistles and the brake system. The worst was when I would get unloaded and then try to shift my tandems before the trailer air bags were reinflated... Not enough air for everything to happen at once. Needless to say, every time I took it in for maintenance I included that as a trouble but they kept saying it wasn't one single leaking point but the combined effect of all the connections and interconnected air systems, each leaking a little from age and wear but altogether equating to a truck that wouldn't hold air overnight. They could have just been B.S.ing me in order to get out of doing something relatively laborious but since I couldn't detect a hiss in any one place it was the most reasonable explanation I could come up with myself. So take it for what it's worth but at least you know which system is affecting your problem which should make it easier to pinpoint.
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