Air leak detector

[aggies09]

Same story second verse, but like all of us, I have developed some air leaks in my auxillary air system. I am somewhat confused as about where to start, but it seems that I remember some of our members having an "ultrasonic" detection device that allowed them to hone in on certain areas. If this is the case, would you please advise what device has worked best for you? Any other thoughts are appreciated as always.

[michaeldterry]

I am most interested in this as well because my auxillary compressor seems to run an awful lot, which indicates that I'm leaking somewhere!

[Jon Wehrenberg]

I know of five ways to detect leaks. Finding and repairing leaks is frustrating, difficult, and time consuming. But when you succeed and get the systems so tight the aux compressor runs once a day you feel great.

Here are the five ways I know to detect leaks.

#1. Listen. (this works for big leaks)
#2. Listen using a stethoscope. (This works for smaller leaks and helps pinpoint their location)
#3. Use soapy solutions. (There are some solutions that are especially effective for finding minute leaks.
#4. Use an ultrasonic leak detector. (good for minute leaks and internal leaks)
#5. Use Freon and a freon leak detector. (last resort. Freon can damage some seals)

There is no silver bullet. Not all methods work in all cases. An ultrasonic leak detector for example will not detect a leak in an air bag. Some leaks may be inaccessible without disassembling portions of the coach like in pocket door mechanisms.

There are some very common leak points that need to be checked first because of the frequency owners have had with them such as the driver's seat or the belt tensioning bellows and the regulator associated with them. There are some tricks also. On a Liberty the converter's aux systems all originate from a manifold in the lower steer compartment. Plug each line individually to see if the leak rate slows down. If it does you can start with that system which could be the driver's seat or the bed lift or the generator air bags, etc.

Here are some facts people tend to get confused about. Air suspension leaks or the leans have nothing to do with aux system pressure. The aux system pressure can be at zero and the bus can still remain perfectly level. Or vice versa.

When the bus is turned off there is no pressure to any of the brake chambers. If there are leaks associated with the brake system (the two gauges on the dash) they are not beyond the relay valves. To check the brake chambers for leaks a DOT pre-trip inspection should be done.

The aux air system is actually split with part of it being the conversion, and the other part Prevost. Leaks in either one will cause a loss of aux air. The Prevost part includes the front door air lock and the belt tensioners for example, but the primary use of aux air on the Prevost is the suspension and the investigation may (will) involve the Norgren valves to an extent.

Good luck guys. I once worked weeks to get my air systems "tight" and my compressor to run only once a day, and a year later it was running multiple times per day. Maybe if I get really bored I will go through the exercise again.

[James]

One quirk with our auxiliary air system is that after we raise and lower the bed there is a constant leak until we shut the aux compressor off, and let the aux air bleed to zero. After that we turn the aux compressor back on and everything’s normal.

Someday I’ll fix that; however, right now we seldom need to raise the bed.

[Jon Wehrenberg]

I can only relate to the way Liberty has set up the bed lift, but it I were to guess, I would look at the valve.

[James]

I can only relate to the way Liberty has set up the bed lift, but it I were to guess, I would look at the valve.

I was thinking it was one or both of the bed air cylinders. Since it doesn't affect anything else at any other time it hasn't risen to the top of the list yet.

[flloyd]

John, is it me or are these two statements contradictory?



Here are some facts people tend to get confused about. Air suspension leaks or the leans have nothing to do with aux system pressure. The aux system pressure can be at zero and the bus can still remain perfectly level. Or vice versa.

The aux air system is actually split with part of it being the conversion, and the other part Prevost. Leaks in either one will cause a loss of aux air. The Prevost part includes the front door air lock and the belt tensioners for example, but the primary use of aux air on the Prevost is the suspension and the investigation may (will) involve the Norgren valves to an extent.


After thinking about it, perhaps I should know that the aux system pumps up the bags, but once the ignition switch is off, the bags are locked and any further leaking in the aux system is somewhere other than the suspension system.

I've noticed on my coach that when parking, I flip the switch to MAN to do leveling. Then, for example, I lower one of the left or right sides by putting its button in the DOWN position. It seems, however, that when I return the rocker switch to the neutral position, the bag re-inflates and the side comes up again. As a work-around, I've been lowering the necessary section and then returning the mode switch from MAN to to ROAD to stop the re-leveling, and then quickly turning off the ignition. I too, am confused with this system.

Steve Bennet mentioned to me that the rear section should raise faster than the front due to the fact that it sits on 4 bags versus 2 for the front end. In my experience, however, the front end raises MUCH faster. It seems that raising the rear can sometimes take minutes and I don't know if I should raise them both at once, or, one at a time.

[Jon Wehrenberg]

Fred,

You have it correct about the air bags as far as locking in the air. All the aux system does with respect to the air bags is supply needed air. Once the air bags have that air, and the key is off the air is locked in the bags and aux system air pressure and internal air bag pressure are separate from one another.

Two corrections. The rear may rise at lower air pressures than the front because it is probably on most coaches that the six rear air bags (4 on the drive axle, two on the tag) each carry less weight (30,000 lbs. divided by 6 equals 5000 per air bag vs 14,000 lbs. divided by 2 equals 7000 per air bag.)

I would doubt if your front raises faster than the rear. The only way I could see that happen is if you engage the tag axle lift leaving only the four drive axle air bags to make the rear go up while at the same time adding more weight to the rear by shifting the pivot point forward. But you would know if the tag axle lift is engaged because you would hear the alarm and see the light on the dash.

The second correction I think is your interpretation of the switch position for leveling. The individual switches that raise or lower the LH rear, RH rear or front work as follows. Press the top of the switch and the valves are closed. Press the bottom of the switch to put the switch into the center position and the valves will supply air to the air bags (raising the coach), and press all the way down on the bottom of the switch and the valves open to deflate the air bags. The center position in not "neutral" but raises the air bags when the main switch is in the "manual" position.