Air usage while under way.

Topic: Air usage while under way. (Read 1468 times) previous topic - next topic

Air usage while under way.

December 02, 2013, 03:33:25 pm

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 – December 02, 2013, 03:42:44 pm

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 – December 02, 2013, 03:47:41 pm

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 – December 02, 2013, 04:01:58 pm

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 – December 02, 2013, 04:34:18 pm

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 – December 02, 2013, 05:30:55 pm

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 – December 02, 2013, 11:03:01 pm

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 – December 03, 2013, 02:19:55 am

Quote from: Yetch – December 02, 2013, 03:33:25 pm

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 – December 03, 2013, 07:43:31 am

Over a period of time, yes it does.
Mike

Re: Air usage while under way.

Reply #9 – December 03, 2013, 11:05:53 am

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

Re: Air usage while under way.

Reply #10 – December 03, 2013, 12:19:35 pm

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 – December 03, 2013, 12:31:09 pm

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 – December 03, 2013, 12:55:27 pm

Quote from: wolfe10 – December 03, 2013, 12:31:09 pm

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 – December 03, 2013, 05:50:11 pm

Actually they work too well below 40#

Re: Air usage while under way.

Reply #14 – December 03, 2013, 06:40:35 pm

Quote from: Dave Head – December 03, 2013, 05:50:11 pm

Actually they work too well below 40#

Yes the rear brakes lock

Re: Air usage while under way.

Reply #15 – December 04, 2013, 07:30:29 am

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 – December 04, 2013, 09:20:06 am

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 – December 04, 2013, 12:39:20 pm

Quote from: Yetch – December 04, 2013, 07:30:29 am

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 – December 04, 2013, 08:13:56 pm

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 – December 05, 2013, 11:09:56 am

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.

Re: Air usage while under way.

Reply #20 – December 05, 2013, 06:03:23 pm

Thanks Scott, good ideas. I stopped off at MOT on my drive down(in my car) and chatted with Mike abit. Found out that the top gage is the left front tank and the bottom is the right, which supplies the rear suspension. He said to check the ride height limiters for the bottom rubber covers, and also the regulator between the two tanks, which I will do when I get home. Both gages go to same limits; 125 on the top to about 105 before the cycle, and both will charge to 125 and remain there when at idle. However, after shut down, they are around 60 within 2 hours or so, and will go to zero within 24 hours.

Re: Air usage while under way.

Reply #21 – December 05, 2013, 08:00:28 pm

Sounds like you do have a leak. The hard part will be finding it. When it gets bad enough you'll hear it, then you can fix it. Don't be afraid of it though. It's probably gonna be an easy fix when you do find it. Even if it's an airbag you can fix it in a few hours by yourself in a campground or even on the side of the road. I've already replaced two of my airbags by myself in a campground. The most difficult airbag on my coach took three hours to replace, mostly because I'd never done one before. The easy one took about an hour. Foretravel says it takes 20 minutes... guess I'll never be able to get a job there! haha

Re: Air usage while under way.

Reply #22 – December 05, 2013, 08:13:59 pm

Mike, there are many areas that can cause that kind of leak if it is not a bag or something obvious. Sounds to me to be as I found the tank check valves maybe allowing air to go back thru the system. Both dry tanks have them and they screw diectly into the end of tank and look like large nuts. I highly suggest you disconnect the 3/8 or 1/2" lines coming too them and get a large wrench on the hex flats on the one furthest away from the tank. Undo it and carefully take it apart. There is a spring and seat in there and if you find a lot of crud in there check the face of rubber seal and see if it has been seating good. Clean it all up good and put back. Do both tanks. The other major culprit is the sliding floor cylinder. That is a tough one to get too. Soap the end of it and I bet you have a nice show of large bubbles. Major leaky item. I posted a couple of leaks I found and how to fix that slide cylinder.
My air emptied like yours but now it stays good for 3 weeks. It has gone down to 50 in 21 days. Pretty good.
John H

Re: Air usage while under way.

Reply #23 – December 08, 2013, 12:34:58 pm

I think I'm going to get a stethoscope and listen to every part of my air system. Has anyone tried that? Can you hear the leaks that way?

Re: Air usage while under way.

Reply #24 – December 08, 2013, 12:44:41 pm

I have used an industrial stethoscope to find an underground water leak. This was a low pressure leak and it took quite a bit of searching to finally locate. Before someone says water and air aren't the same, I'm just saying that I found a water leak.

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