Some may remember that I have been, for some time, chasing a stubborn air leak from our wet tank. If I parked the coach in the evening with 100 psi in the air system, by next morning the wet tank would be empty, while the front and rear tanks would still be holding around 80-90 psi. SInce the front and rear tank check valves were working, the leak was obviously in one of the air lines coming off the wet tank. I looked everywhere I could think of, to no avail. I was totally baffled.
Skip forward to our current road trip from TX to Oregon. Our second day on the road, the air system started to act erratically, with the compressor load/unload points drifting up and down. Also, time between unload and load was decreasing, indicating a loss of air that was escalating. Standing at the engine compartment hatch, I could hear air constantly escaping from the purge valve on our AD-9 air dryer. The air compressor was able to keep up with the air loss, but it was working way too hard. I tried adjusting the set screw on the D2 up and down, and it seemed to help a little, but something was obviously still amiss.
We arranged to stay in our current RV park a extra day, so I could work on the problem. Since I was carrying a spare D2 governor and a spare AD-9 (rebuilt) dryer, I decided to do some swapping. I really did not want to get into changing out the complete air dryer while traveling - I much prefer doing that job at home in my driveway. Having done it myself once before, I knew what a pain it was. Instead, first, I replaced the faulty D2 with the new one. Then, I removed the fresh purge valve from my spare rebuilt dryer, and installed it on the coach in place of the malfunctioning valve. When I removed the leaking valve, I found one of the O-rings (the center one) was badly damaged. It had obviously been pinched and torn almost in half when the valve was originally installed in the dryer base. Shows that even genuine Haldex/Bendix rebuilt dryers may not always be totally trouble-free.
Fired up the coach, and the new D2 started controlling the compressor perfectly. The leak from the air dryer purge valve was also totally cured. But the REALLY surprising result became evident after I shut the coach down with 110 psi in the air system. Now, some 6 hours after I finished working, the air system shows 100 psi - on ALL 3 TANKS! Replacing the D2 and the purge valve has apparently cured the wet tank leak! I still do not understand what path the escaping air was taking, but at this point I will happily accept the unexpected bonus!
Follow up report - the morning after. It is now about 18 hours since I completed my repairs. We now show 70 psi in all 3 air tanks, down from 110 yesterday mid-afternoon. So, I still have some air "seepage" somewhere in the system, but at 2.2 psi per hour, I can live with it until we get back to home base.
The good news is, my wet tank is showing exactly the same pressure decline as the front/rear tanks. This is the way it is supposed to work, and verifies that the massive leak I had in the wet tank is undoubtably fixed.
When we get to a suitable location. and I have the time, I will dissect the two faulty components and try to determine the failure mode. I did note when I removed them that the ports on both the D2 and the purge valve were partially filled up with "trash"...kind of a grainy, yellow-brown material that looks sorta like sand. It is not the dreaded "white powder" associated with dryer failure. Where did it come from? I am pretty sure this is the cause of the dual malfunctions. I will post some photos to this thread when I do the teardown inspection.
I mentioned the torn O-ring found on the old purge valve. I don't think this had anything to do with my air leak, because we made another trip to Oregon last fall, with this same air dryer in place, and it worked fine. I just mentioned the O-ring as something to keep in mind - never assume any rebuilt component is perfect. They are, after all, assembled by (fallible) humans.
Follow up follow up report - road test. Drove about 200 miles today - Declo, ID to Caldwell, ID. Our old coach just purred down the highway, and the air system functioned perfectly. I must therefore declare my repair job a success. ^.^d
I strongly recommend every member carry a spare D2 governor, and a rebuild kit (if applicable) for your air dryer purge valve. Having these parts on board saved me a BIG headache!
If you are ever in the Caldwell, ID area (just west of Boise) and need a place to stay, we recommend the Ambassador - extremely nice RV park.
Ambassador | Grapevine 7 (http://www.g7rvresorts.com/idaho/ambassador/)
Chuck,
Excellent detective work! Looks like your main problem was a leaky purge valve . I did a lot of soap bubble testing of my compressor and the governor while running to look for leaks at the connections, hoses, and the governor itself. With the dryer removed and the by-pass used you can make sure your unloaders are working as they should with just the governor cut-in and cut-out. With a leaky governor, the reserve tank line feeding into it could be a source of air. A dirty governor with trash in it from the system would be suspect.
Internal leaks in the compressor will have to be tested separately with an air source from your shop compressor. With the lines removed, air pressure back into the inlet, discharge, and unloader ports will detect leaking valves. In my case I couldn't find any leaks, but the unloaders were stuck shut and not working at all!
Here's video on an easy way to bench test your air dryer and a couple more on compressor maintenance.
Happy hunting!
Jerry
http://www.youtube.com/watch?v=CpVaHnZds_Q
http://www.youtube.com/watch?v=VeyFaEP8FKA
http://www.youtube.com/watch?v=JZM2NFExZsA
Jerry,
Great videos! Thanks for posting. ^.^d ^.^d ^.^d
see ya
ken
What is the part number or link for a rebuild kit for the purge valve?
Assuming you have a
AD-9 dryer, you have a choice of what parts you carry. From cheapest to most expensive, you could carry:
1. A "minor maintenance" O-ring kit
2. A remanufactured purge valve assembly
3. A complete remanufactured AD-9 dryer
I happened to have a complete dryer with me, because I was planning to change ours out in the near future. So I just pulled the purge valve assembly out of the rebuilt unit, and swapped parts.
Just looking quickly at online prices, it appears a reman purge valve assembly might cost almost a much as a complete dryer. I'm leaving the core charge out of the equation, because you always eventually get it back. I buy my reman dryers at NAPA, both to insure that I get genuine Haldex/Bendix parts, and because you can return the core for your refund to any NAPA store nationwide.
Part numbers below:
Product Search (http://www.haldex.com/en/North-America/products/product-catalog/product-search/?psq=109685x&filter=0)
When I search for AD9 I find Bendix, Haldex and Midland. All claim to be genuine OEM. Anyone know the relationship between these companies?
see ya
ken
My understanding, which may be totally wrong, is that Bendix originally designed, patented and manufactured the AD-9.
I guess you might still find brand new AD-9 dryers built by Bendix? However, I am having trouble actually finding anyone who stocks them.
Haldex is a rebuilder of the AD-9, and sells the rebuilt units as part of their "Like Nu" line. This is the (rebuilt) AD-9 I buy at NAPA.
Haldex also owns the Midland brand name, and sells new and rebuilt components under that brand. There are also "Midland" (rebuilt) AD-9s.
It may be picky, but I have always used FACTORY reman by the factory that originally built the dryer.
Yes, there are a lot of "replaces AD-9's" on the market, just like a lot of other knock-off parts.
If having trouble finding one, contact Bendix.