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Author Topic: air compressor cycling every 5 minutes, MC 5C  (Read 3236 times)
luvrbus
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« Reply #15 on: July 27, 2011, 07:03:05 AM »

Buy you a bottle of Big Blu leak detector it will find it for you but most likely you will find the shut down leaking they do some weird stuff

good luck
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eddiepotts
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« Reply #16 on: July 27, 2011, 07:21:56 AM »

I found my air line going to the purge valve was leaking. I could not hear it very long after the bus was shut down but found it when I ran my had along it while it was running. I was not purging but constantly blowing when running.
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lostagain
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« Reply #17 on: July 27, 2011, 11:50:24 AM »

Just crawled out from under the bus for lunch.

The comp. recovery time at 1000 rpm is down to 1 1/2 mn from 2 mn at 700 rpm. Not great, but better.

I confirmed that it does not loose air while running, just sitting there. It doesn't leak when shut off either.

I then disconnected the levelling valve rods and exercised them up and down and they work as expected, no leaks there.

There is no shutterstat anywhere that I can see. That was removed when the 6V92 was installed.

I also checked the shut down circuit, as well as the fast idle air lines, etc, : no leaks either, but like I said the air press. doesn't go down just sitting still, only when driving down the road.

So now I am thinking about finding all the various check valves to take a good look at them and replace if necessary.

If there is a bad check valve, wouldn't air go back to the compressor while compressing, therefore explaining the slow recovery time? And off course, a partially open check valve would let air out back to the compressor?

I can't think of another way air would leak only when driving.

JC

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JC
Invermere, BC
1977 MC5C, 6V92/HT740
luvrbus
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« Reply #18 on: July 27, 2011, 12:22:30 PM »

A bad discharge valve on a compressor will make the compressor circulate air but you say you rebuilt that, it only has one and is under the head not like the unloader valves


good luck
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Busted Knuckle
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« Reply #19 on: July 27, 2011, 12:25:09 PM »

JC,
FWIW I just had one acting up several weeks ago and had trouble figuring out the problem. We replaced the drier cartridge and I rebuilt the purge valve. (and dad was doing other things as well).
When we got done it was cycling worse than before we did all this and we went back and re-did things one at a time. All said & done it turned out I accidentally put the purge valve back together backards and once I re-did it our problem went away.

So we really don't know what the cure actually was because we didn't take it one step at a time, but rather just did a group of things we knew needed done anyway.

But in the end we do know that I cost us more time & aggravation by my own mistake of putting the purge valve back together wrong. (as soon as I switched it around and could actually feel the difference it made in feel I knew what I had done!)
Grin  BK  Grin
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Busted Knuckle aka Bryce Gaston
KY Lakeside Travel's Busted Knuckle Garage
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www.kylakesidetravel.net

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eddiepotts
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« Reply #20 on: July 27, 2011, 02:50:27 PM »

I was just thinking that if your compressor keeps running it will over presser your relief valve on the air dryer and blow constantly. Check to make sure it is not your relief valve is leaking causing it to relieve and not because it is over pressuring. I also just rebuilt mine. your check valve on the dryer will keep the bus aired up and the valve will quit relieving when the dryer runs out of air which will happen quick. There will be no noisy leak after shut down if that is it.
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lostagain
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« Reply #21 on: July 27, 2011, 05:26:05 PM »

The dryer purge valve I replaced was new. All I had to do was put on the O-rings, grease them with the supplied grease and slide it up and put on the 3 bolts. Pretty hard to screw up, although, knowing me, possible, LOL.

I looked at the check valves on the dry air tank. I can just see them, behind the generator enclosure in the drivers side baggage tank... I could possibly turn a wrench on them maybe 5 degrees, if they are not too tight... So I will leave them alone for now.

Since there is no leaks sitting in the shop running or not, I think I will take the bus for a drive tomorrow, and when it starts loosing air, I can stop and at least spray soapy water on all the air connections I can reach in the engine compartment ( shut down cylinder and lines, fast idle, etc). I could have the door claw engage, then off. Trying to narrow it down as much as possible to see under which conditions it leaks, without the wife and kids, trying to get somewhere. Just replacing parts without knowing what is wrong is not the way to go.

I could have my son step on the brakes while I watch the R8 relay valve, and the quick release valves.

I'll take some blocks with me so I can look underneath as well: spray, spray, LOL.

I got to get this resolved,

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
eddiepotts
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« Reply #22 on: July 27, 2011, 05:37:16 PM »

I am not talking about the purge valve. Check the relief valve. That's what keeps your dryer from over pressuring. Mine hung vertical so the water would set on the ball until it rusted out and started leaking. It should look like a whistle hanging off the side of the dryer.
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lostagain
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« Reply #23 on: July 27, 2011, 05:39:22 PM »

Thanks Eddiepotts, good tip, I'll look into it tomorrow too.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
eddiepotts
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« Reply #24 on: July 27, 2011, 05:43:38 PM »

Here is the link to my relief valve problem. http://www.busconversions.com/bbs/index.php?topic=19746.msg215128#msg215128
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hargreaves
1987 MCI 102A3
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« Reply #25 on: July 27, 2011, 06:23:53 PM »

Hey JC one test it looks like you haven't done is, block wheels - release parking brake - apply service brake- check for leaks. the anti compounding valve may be not letting air to the service brakes. you may have a service brake maxi diaphram leaking.  Gerry
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now as of Feb 2012 series 50 B400  . Sunshine Coast British Columbia
lostagain
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« Reply #26 on: July 27, 2011, 07:02:41 PM »

Gerry, I don't see an anti compounding valve in the maint. manual diagram. I have DD3 brake chambers on the drive axle. Is that why?

I don't have the feeling that the leak is related to the brakes: going down the freeway without brake applications, the air press. goes from 125 to 90 psi in 3 to 5 minutes. But what do I know?

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
Gary W
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« Reply #27 on: July 27, 2011, 09:07:47 PM »

Jc

When I replaced the Allison 740 transmission, Cullen Diesel which did the work said they blocked off a air line that ran to a skinner valve on the trany from  the compressor . They said  it wasn't needed and it was leaking transmission fluid. I don't know if you have the same set up but it might be worth checking. Maybe if you have that valve it might leak air when you put it in drive.

Gary
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hargreaves
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« Reply #28 on: July 27, 2011, 11:15:06 PM »

sorry JC didn't realize you had DD3's. Air throttle?
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now as of Feb 2012 series 50 B400  . Sunshine Coast British Columbia
olebusman
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« Reply #29 on: July 28, 2011, 07:21:32 AM »

  Just replace the screw in check valve in/on the AD9 drier. Leaking back thru  olebusman
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