One of the issues I have in these threads is nomenclature. I don't know what low pressure switch or purge valve look like or where to find them. I assume the purge valve you are talking about is the one on the bottom of the glass bulb of the half dozen dryers on board. My ignorance of air systems is overwhelming but I will be learning fast.
Jack and Dianna Hunt
Coach #663
2003 - 45' triple slide
Let's split th e system into two major systems to start: there are two gauges on the dash; the dual needle brake gauge and the single needle supply gauge. If the supply drops and neither of the brake needles drops with it then you can eliminate the brake system. If one of the brake needles drops with the supply until the supply hits 70 and then the brake needle continues to fall but the service holds pretty well then you need to check the brake system for leaks.
Assuming it's the service needle that's falling but not the brake needles, then we need to split the rest of the system in half if possible. On my 93 coach there are a pair of ball valves on the bulkhead just ahead of the drive axle. Closing those valves separates the leveling system from all the other "service" uses. The pressure gauge at the rear 6-pack shows the pressure on the leveling half and the dash supply gauge shows the pressure for everything else. Seeing which one drops the quickest tells you where to look..
Given that the rear drops when pressure drops, but the rear stays up when in leveling mode suggests the leak is somewhere between the supply to the 6-pack and the 6-pack and includes the HCV's since the HCV's are not isolated from the supply air when in leveling mode, their output is only isolated from the airbags.
All three needles drop to almost nothing as best as I recall, I will try some different scenarios and pay more attention to the stop points on the various needles. Micheal Day had suggested a problem with the HCV's as well.
Jack and Dianna Hunt
Coach #663
2003 - 45' triple slide
A leak at the HCV's which are supplied from the service tank will not cause the brake pressures to decline since there are check valves in the air supply lines from the service tank going to each of the brake tanks.
It would be very helpful if we had a diagram of the air system. You can find a system for trucks online, which is helpful, that does not include all the other air powered stuff on our coaches. If you take the truck diagram and add the HWH diagram you will gain a lot of useful perspective.
Sent an Email to Mike at Newell seeking an air system diagram, don't hold much hope of getting one. Probably have to create my own as I trace everything down. I went out and ran the engine to air things up and see how it reacted, the steps are laid out on the attached PDF. Coach was parked without the leveling on, seemed pretty close to ride height and level.
Jack and Dianna Hunt
Coach #663
2003 - 45' triple slide
(This post was last modified: 08-15-2018, 07:33 PM by Jackflash.
Edit Reason: spell check
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The primary air leak appears to NOT be in the brake system although the check valves in the brake system could be causing it to leak down too fast also. You are losing nearly the full air supply in the non-brake air circuit in two minutes without leveling on and not much slower, maybe 3 or 4 minutes with the leveling system on. That is a MASSIVE air leak.
As soon as you shut down the engine, can you hear the air leaking outside, especially back by the engine? That is stunning!! I have never seen an air system leak down 60+ pounds in two minutes! Certainly a large fitting that has split or come off, a split in a large air hose, or even a split/hole in the wet tank itself could cause a leak that large. I would NOT think that a 1/4" air line could leak down that quickly. An air bag that has come unseated might leak air that quickly. Still way too many possibilities at this point but it looks like focusing on the non-brake systems first you be your best bet.
You should be building air in your brake system to about 110-120psi within minutes at no more than fast idle--1,000 rpm. Air govenor or engine air compressor bad? Or you have the biggest air leak ever seen that cannot be heard.
I believe you mentioned that the on board (electric) air compressor would not keep up with the leak without the engine running, that would seem to point to a massive leak. You also mentioned the 'kinking' of the air line to the toad when you drug the rear end about the time the massive air leak started. I would pay particular attention to the air line that feeds that connection and confirm there isn't a problem along the path of that air line.
Have you tried putting the coach in a quiet environment, hooking your pancake air compressor to "shop air" and looking for a leak? What tools have you used? In its current condition, your coach does not pass the basic daily brake test & your coach should not be driven until the problem is corrected. If you do not have the ability to find and correct the issue, consider a mobile mechanic.
