air compressor operation, and leaks?

[Homegrowndiesel]

After a normal initial cold start, and initial air charge On our MCI 102 A3 the air compressor governor trips and the compressor builds air, till the pressure rises to the cut off at 115-120 pounds, then the governor kicks in and trips the seperator to cycle its regeneration cycle, it blows down, shuts off, then the pressure starts dropping, till the governor trips again at around 95 pounds and starts the cycle again. All seems to be working correctly, Except,,,,, the cycle is too quick. the air is dropping way to quick, I can only drive two miles before the cycle starts again. When I shut down the engine and listen for air leaks I can't hear any air leaks (yes I used to hear some, but have corrected all that I found) and am at a loss as to why, or where the air is leaking. I am thinking maybe a check valve that is letting the air return back thru the compressor intake? After shutting off the bus the pressure drops to nothing within hours. I replaced the compressor and governor several thousand miles ago, and it builds air fast. I guess my next check is to remove the hose from the air compressor intake to air cleaner plenum to see if it is back feeding? Any other insights?

[lostagain]

Is it in the braking system? Do your pre-trip inspection to see if it holds air.

Is it in the suspension? Does the bus stay up while the air leaks out after shut down?

Process of elimination.

I had a leak this summer that I narrowed down to occurring while underway with the door claw engaged. I still could not hear it, but it was the supply hose to that cylinder in the spare tire compartment, and it could not be heard until I crawled in there.

Perseverance...

JC

[buswarrior]

I'd be looking for leaks, never mind the fancy leak back thoughts for now.

Every exhaust port on every brake valve, soapy water on the suspension leveling valves, you got shutters/dampers and the related controls?

The body of every valve, the end where something moves, the lines, the sensors, the drains of tanks, the tanks themselves, especially at the bands, good catch on the last post, the door lock, the wiper system if air powered...

You have a lot of dish soap to put through the spray bottle.

keep it simple, a little bit of knowledge leads to the dis-assembly of perfectly good parts and a waste of many hours that could be spent moving forward.

happy coaching!
buswarrior

[Homegrowndiesel]

Jc, It does not seem to leak any faster with the brakes applied, and the bus does not stay up, goes down as the air pressure goes down.
BW, Yea, looks like there is alot of soapy water in my future ,,:(.

Just funny, as I could hear air leaks here and there, and fix those with no difference on the leak down time, yet losing that much pressure so quick and not hear anything seems strange. Just checked on a calm quiet night and still can't hear any. Oh well seems a trip over the pit is in order, with some soap.

[bevans6]

First thing is that the check valve that separates the compressor from the air system while the compressor is not charging is at the air dryer connection to the wet tank, so the compressor has nothing to to with that at all.  Second is that if the air suspension is dropping, determine where and which load points - they have check valves that separate them from the air system as well, so if the suspension is dropping, that corner is losing air somewhere.  That much air isn't going to be that hard to find, best thing to do is hook up to an external compressor so you don't have to keep running the engine.

Brian

[Nick Badame Refrig/ACC]

Hi Bill,

If your whole suspention is dropping, I would check the leveling valves too. They are notorious

for going bad in our 102's. I also couldn't hear them leaking when they were infact leaking badly..

Good Luck
Nick-

[Len Silva]

Air leaks are part of life in these old buses, and a constant source of problems.  If I had it to do over again (not likely), I would install isolation valves in various parts of the system to aid in locating leaks.

Good quality ball valves are not expensive.  You could install them in the suspension system, other aux air supplies, etc.  Not sure I would put one in the braking system though.