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Topic: Air usage while under way. (Read 1738 times) previous topic - next topic

Air usage while under way.

I took my coach out for about 50 miles of exercise, and I was noticing how the air gauges were reacting to the ride.  I have a few questions about the air system.  Of the two gages, I'm assuming that the top gage is the front system, and the bottom is the rear, or master?  I noticed that the bottom gage was recycling continuously, while the top gage remained pretty constant.  Can anyone comment and explain the reason for this, or direct me to some threads that can explain this system for me.  I know I have leaks somewhere as the system won't hold air for long after shutdown, and I have gone over most of the obvious fittings underneath, but is the cycling in the lower gage normal while driving?  The roadway was not extremely smooth, but not overly rough, either.  There was some working action in the suspension.

Thanks, Mike

Re: Air usage while under way.

Reply #1 –
The only systems that "use" air are 1 the air bags.. Air leveler valve working normally releases air which in turn causes bag to require air to replace.. 2 is air brake's.. the more they are used the more air is drawn from supply tank... Any more beyond that is a leak... I know nothing of coaches with slides.

Re: Air usage while under way.

Reply #2 –
I have a Freightliner diesel rig on the yard right now that my mechanic has gone over with a spray bottle twice.. Have fixed every leak we can find.. Still I can turn off the engine and go out there 1 hr later and it has dropped 25lbs... Driving me nutts because I want a air system to be air tight be it on my Foretravel or 1 of my diesel trucks. Small air leaks can run a guy to foul language.

Re: Air usage while under way.

Reply #3 –
Having just gone thru this system extensively I can now recommend taking off the one way check valves at tanks and air dryer as if not holding correct air leaks back thru the system and out. This was my major leak along with the air cylinder for stair slide cover, and the foot valve for air brakes (tough one to get too and fix.
John H
ps-- my air tank pressure after 2 weeks is still at 70lbs- both tanks. Previously it would leak down to 30 overnight.

Re: Air usage while under way.

Reply #4 –
You've got that suckerbill air tight John... I need to get you up here and under some diesel trucks and take my mechanic to school.

Re: Air usage while under way.

Reply #5 –
 Those check valves hardly ever get looked at I believe and simple to take off and apart to clean or replace.
John H

Re: Air usage while under way.

Reply #6 –
Ride height valves can consume a lot of air. Rear axle moves quite a bit while driving, even more so on uneven roads. Every bounce will change ride height, cause air bags on one side or the other to dump air and fill bags, draining rear brake tank. We always see our rear tank go down and then at about 90 psi, refill. Front tank is much more stable as the single front ride height does not bounce around as much as the rear. Sounds normal to us.

Re: Air usage while under way.

Reply #7 –
Quote from: Yetch –
I took my coach out for about 50 miles of exercise, and I was noticing how the air gauges were reacting to the ride.  I have a few questions about the air system.  Of the two gages, I'm assuming that the top gage is the front system, and the bottom is the rear, or master?  I noticed that the bottom gage was recycling continuously, while the top gage remained pretty constant.  Can anyone comment and explain the reason for this, or direct me to some threads that can explain this system for me.  I know I have leaks somewhere as the system won't hold air for long after shutdown, and I have gone over most of the obvious fittings underneath, but is the cycling in the lower gage normal while driving?  The roadway was not extremely smooth, but not overly rough, either.  There was some working action in the suspension.

Thanks, Mike

Not that I think my next comment is related to your air gauge movement but it might be.

My 5132 coach like the other coaches shocks were all set at full soft.  There are five adjustments. 

My coach had a fair amount of pogo over large radius bumps in the road.  After adjusting the fronts which requires pushing the shock together then turning it 1/2 turn for each firmer adjustment I had them set at three.

Big improvement but still not very firm.

Upon examination I noticed all the wheel wells had marks from the tires rubbing against the floor directly over the tires.

The rears were on the outside edge as primarily body roll was causing contact between the tire and the floor.

Hmmmm.  Took the coach back to the shop and told them to turn all of them up to the fourth setting.

Now it's dampened.  Up and down you can feel you actually have some shocks in the coach.

Quickly noticeable was the much less body roll on tight corners. 

Mechanic said the rears could be compressed by hand upon removal.  After adjustment he could barely compress it.  Which is correct as far as I know.

You have 20,000 pounds trying to move up and down.  Needs shocks.

Too loose and the ride height valves probably wear quicker?

The only things stopping the coach's subframes from up and down movement is the air pressure in each bag and the shocks.  The air pressure depends on the load and is not adjustable so alls that's left is the shocks. 

Cycling on one axle I would think is a fair sized leak.  Does the coach loose height when parked with the leveling system and engine off?

Re: Air usage while under way.

Reply #8 –
Over a period of time, yes it does.
Mike

Re: Air usage while under way.

Reply #9 –
Wow, mine cycles about every 10 to15 mins.  Worse in the mountains best on flat land.

Re: Air usage while under way.

Reply #10 –
Dave,
When you say 'governor cycles', do you mean you see a decrease on your air gages, and then an increase?
Mike

Re: Air usage while under way.

Reply #11 –
Yes, as Dave said, the air system GOVERNOR "turns on" (actually closes the exhaust valve on the compressor) when pressure reaches CUT-IN pressure and "turns it off"  (opens the compressor exhaust valve) when CUT-OUT pressure is reached. 

Said another way, the governor's job is to only take HP to run the compressor when it is needed.

BTW, other than air brakes and air suspension, many coaches have air throttles that do take air, particularly when changing throttle position a lot.

Re: Air usage while under way.

Reply #12 –
Quote from: wolfe10 –
Yes, as Dave said, the air system GOVERNOR "turns on" (actually closes the exhaust valve on the compressor) when pressure reaches CUT-IN pressure and "turns it off"  (opens the compressor exhaust valve) when CUT-OUT pressure is reached. 

My governor stuck closed every so often and the pressure it allowed was 10-15 psi low before replacement.  Brakes work better with more pressure.

Bob

Re: Air usage while under way.

Reply #13 –
Actually they work too well below 40#

Re: Air usage while under way.

Reply #15 –
Brett,
How would I know if there is an air throttle?  My cycling was going on with cruise engaged on rolling hills with trans in economy mode.
Mike

Re: Air usage while under way.

Reply #16 –
Mike,

Some Foretravels used the Bendix air throttle.  If so, open the engine compartment (raise bed) and look for the throttle attachment to the engine.  trace it back "up stream".  If it goes to a cylinder on the front engine compartment fire wall that has a 1/4" air line going to it, you have one.

But, more of the electronic engines use drive by wire/electric throttle to the ECM.

Re: Air usage while under way.

Reply #17 –
Quote from: Yetch –
Brett,
How would I know if there is an air throttle?  My cycling was going on with cruise engaged on rolling hills with trans in economy mode.
Mike

Yours is electronic as is the complete engine as far as I know.

Bob

Re: Air usage while under way.

Reply #18 –
Ok, thanks.  I'm back to flying in the Gulf for 3 weeks so it will be a little while till I can start looking into the problem again.
Mike

Re: Air usage while under way.

Reply #19 –
What Barry said... Your air ride system adjusts itself constantly as you're going down the road. Bumpy roads cause it to use more air for adjustments. If you've got a significant air leak, like a blown airbag or something, you'll know right away because one gauge won't be able to get back up as high as the other one and you'll lose pressure on that gauge quickly when you shut the engine off. You'll probably hear the air leak hissing when the coach isn't running. The coach will probably start to sag on those particular airbags soon after you shut the engine off. If you do have a leak don't panic. You can fix it yourself on the side of the road. Air leaks are some of the easiest repairs you'll ever have to do. Carry a spare airbag with you, along with the correct wrenches and a low profile heavy duty bottle jack. You might also carry some air brake hose with you... I actually need to get some air brake hose to carry with me so thanks for causing me to remind myself to get some. :))