When we replaced our air dryer a couple of years ago with a rebuilt Haldex, I did not know what the part on the input port was so we just moved it to the rebuilt dryer.
Later we learned that it was an add-on isolation valve, and wanted to carry a spare valve to be installed if there was an air dryer problem.
Attached is the documentation on the valve. We purchased the Haldex part from Wheeling Truck for $92 + $8 shipping.
Haldex Midland Isolation Valve KN23500 | Wheeling Truck Center (http://www.class8truckparts.com/Haldex-Midland-Isolation-Valve-KN23500/M/B0046P1C8E.htm)
Invoice shows p/n MIDKN23500.
Installation Guide shows OEM p/n N15842F & N15842G and Service p/n KN23500.
Box shows p/n HALDX 8075792.
Barry, What is the purpose of an isolation valve on the air dryer ?
Gary B
I don't know what the isolation valve does. It was on our original and moved to new dryer, so now I have a valve to replace the original that I will put on if I have a problem with original.
I hope someone can explain what the valve does. I am pretty sure if dryer needs one and it is missing, there will probably be oil blow out from bottom of dryer.
I also have a question on why our rebuilt air dryer had an additional brass valve in a vertical recessed hole in the air dryer bottom that was not on our original. This is not the air pressure relief valve that is horizontal on dryer bottom which both have.
Barry,
A simplification of what the valves purpose is, it seals off the dryer from the outside world when the air compressor isn't pumping air. (or put another way an upscale check valve) This can be during the time the governor has the compressor kicked out or when the engine is shut down.
As a side note there is a piston inside that has 2 o-rings and if they are bad then you can have an internal air leak that you can't find with bubbles as the air escapes backwards through the system. Years ago there was a rebuild kit for those that contained a new piston, rubber seat, & o-rings.
Pamela & Mike
I don't think I have one on my 2003. I thought I read somewhere that Foretravel stopped using them at some point. Is the valve necessary and could there be something in place of it on the newer coaches or is it a different air dryer that does not need it?
Mike & Pamela,
Thanks for your explanation. It makes sense on what is saw when it was off the dryer. One of our Forum members thinks the absence of the valve was the source of excess oil blow out from bottom of dryer.
Do you know anything about a brass valve looking thing in a hole in the bottom of our rebuilt dryer? It was completely missing from original dryer. This is not the pressure release valve the we are supposed to replace with new filter kit. The valve in question was completely flush with bottom of dryer, so no part of the valve sticks out from bottom of dryer, as only the end of the valve is showing. I could not find the valve on replacement parts explosion.
Barry,
This is just a quick guess as to what you have. If you exchanged your dryer rather than rebuilding it youself they most likely gave you the new style dryer that is compatible with the style "E" compressors. If I remember correctly the old style DA 33100 X wouldn't work with the Hoslet compressor so they reworked the base and called it the DA 33200 which will work with any compressor. I would have to call my parts place (closed on the weekend) to see if Haldex has added that valve in either the DQ 6020 lower repair kit or the DQ 6026 general repair kit.
Hope that this is some help as it is just a WAG
Pamela & Mike
Make sure you search around. Amazon's prices are high. Ryder Fleet products look good.
Rather than carry spare parts for my dryer, I carry a bypass kit ($12) so I can worry about a replacement later.
Barry,
If the forum member had an Isolation valve like you listed and it was removed here are some random thoughts in no real order of importance:
There should be a 1/4" line that comes off the top of the wet air tank that should be close to the dryer. This would have a plug in it and may have been hidden in one of the looms. They may also find a plugged line that comes from the governor feed. These are what moves the piston inside the isolation valve.
If there is no check valve between the air dryer and the compressor there is a chance that when the governor unloads the compressor, the compressor is "breathing" through the dryer rather than back through the intake. If this is the case then you could have an excessive amount of oil coming from the purge on the dryer.
Some applications I have seen (on trucks) they used a simple check valve.
If a shop changed out the dryer rather than rebuild the old one I can't see why they wouldn't question what the airlines that make the isolation valve work are for. They would have to remove those lines to get the dryer out. Just looking at the isolation valve you can tell that it is more than just a standard pipe fitting.
If the forum member wants to P/M me about this I will be more than willing to kick some options around.
Pamela & Mike
Barry,
It came to me that I have a DA 33200 on the shelf. Is this the part you are talking about? The pressure relief valve can be seen to the right in both pics.
Pamela & Mike
Pamela & Mike,
YES YES YES
It is on our rebuilt dryer installed in our coach (and with the original isolator valve).
What is it do to work with Holset compressor? How does it work with our compressor? Interesting how a rebuilt dryer continues to have advantages over replacing just two filters.
THANK YOU.
Barry & Cindy
OK, here is what happened. It's a long story but I'll try to keep it down. I meant to do this a year ago and didn't get around to it, but since the subject has surfaced again it is probably worth getting the story out there.
It March of 2009 we got a used U320 with 98,000 miles (which we named E3).
In the 3 years that followed I was plagued by a constant rain of goopy oil covering the hitch and toad. At first I thought it was just from engine leaks/blowby but finally figured out it was coming from the air dryer. During this period I tried just about everything to figure out why the air dryer was spitting oil and get it fixed. Among a lot of other things, I wound up replacing the air compressor twice. I did notice early on that I had a Wabco air dryer and every other FT had a Haldex (or Midland-Grau which Haldex has since acquired).
Took it in again in Feb of 2012 and finally found a mechanic who recognized the problem and figured out that it should have had an isolation (also called Econ) valve installed, which it did not. So I started doing some research to answer a lot of questions - like, what the heck was an econ valve, do I really need it, does every other FT have it or need it, if I did need it why didn't I have it, why did I have a Wabco air dryer instead of Midland-Grau, etc.
Here are excerpts from an email I sent to Barry Leavitt in Feb of 2012. I had been talking to Barry and Harvey Nelson at length about the problem for quite a while.
"I think I am getting close with the air dryer. I am going to pickup E3 on Monday. It has been a great journey of discovery. I know much more about air dryers than I ever wanted to know.
Here is what I think I know now.
My M11 engine and I'm guessing probably all of them had the Holset Type E compressor. The Holset Type E requires the use of an Econ or isolation valve. At that time FOT was using the Midland-Grau N4250 air dryer. I think it may have been available in an "E" version (which would have had an integrated econ valve) but don't know whether FOT used that or an external isolation valve. Yours used the external valve and it shows on your air system diagram.
In about 1999 Cummins switched to using Wabco air compressors, and the issue went away. That is why Harvey ( who has a 2000 U320) still has the original N4250 air dryer with no isolation valve. At this point I am wondering if my RV somehow got out of the factory with an incompatible combination - namely a Holset E compressor and an N4250 air dryer with no isolation valve. I checked with the factory and the air system diagram for my coach does not show an isolation valve, so if it didn't have an N4250E, that would have been a problem. I need to call the factory back and verify the the exact model of the N4250 for my build.
I was curious about what a Holset Type E compressor is, so I called Cummins and got someone who was able to point me to Holset. Found someone there who was very helpful.
Here's an excerpt from my notes of that conversation
Talked to the guy at Holset. Cummins now owns Holset. He knew all about the problem. Finally found the right person to talk to. Cummins used Holset compressors up until about 1999, then switched to compressors made by Wabco, which were lighter and more efficient. Checked Harvey's engine serial number 34982899 and he had a compressor with Cummins part number 3558163 as original eqpt. This is the Wabco type. They are not bolt in replacements. Wabco has some different fittings, I think for coolant. So if I want to replace the compressor I have to stick with a Holset. The non-Type E model would likely be 3047440 "standard 296 (relates to head size, 13.2 cfm model)".
He said that the SS296 came in both E and non-E versions. The E version was designed to use "engine boost" where the input line is boosted by engine pressure to make it more efficient. But it does suck a vacuum when it is unloaded and so it pushes oil past the rings and down the output line so it needs a special dryer, with an Econ valve. Used to be they added the external econ/isolation valve but this had a problem with freezing up in cold weather so they came out with air dryers that had integrated econ valves, like the wabco 1200E and Bendix drop-in.
I asked about how often he had seen an incompatible combination, E type compr and standard air dryer. He said he sees it all the time and it didn't surprise him. Said that some people have replaced the compressor 5 times trying to fix it. It doesn't show up in stop and go, where the compressor is working a lot. Only shows up in long haul on highway where vacuum has time to build up.
Apparently very few mechanics are aware of this, so if you somehow acquired this problem it can persist for a long time. I was originally going to just add an external isolation valve but then decided since the old Wabco air dryer had spent so much time submerged in sticky oily goo, it just made sense to replace it. So I ordered a Haldex DA33200x, which is the version with the integrated econ valve."
As I wrote to Barry in the email above in Feb 2012, the fact that Barry's air system diagram showed the isolation valve and mine did not led me to question whether it had ever been installed in the first place. Since then I've come to the conclusion that my RV was probably fine when it came out of the factory, with the N4250 air dryer and an external isolation valve just like all the rest of them. I still don't know why the diagram for my air system doesn't show it, but I'm pretty sure it was probably there and disappeared when the Wabco air dryer was put in. I tried to track down the maintenance history to see why the original 4250 air dryer was replaced with the Wabco. I am very curious about that since an air dryer failure is not a common event, but there had been several owners and the information simply was not available. It's hard to imagine a mechanic doing a replacement, finding an attached part, and throwing it away without understanding what it was and why it was there, but right now that seems to be the only explanation I can come up with.
This problem drove me crazy for 3 years. I believe it is a six-sigma outlier as far as problems go. During those 3 years I talked to many service facilities and mechanics and did a lot of internet research and never got any closer to solving it until I finally talked to one mechanic who had heard about it. The person at Holset had seen it in the trucking world, but it obviously wasn't that common there either or that one trucker would not have replaced 5 compressors looking for the answer.
To the best of my knowledge no other FT has ever had this. It would only apply to the older coaches, 1998-1999 and previous, before the switch to Wabco air compressors. So I don't think it is a big issue for this group, but it's a good thing to know about just in case.
BJ, Your story proves that Murphy's law is omnipresent. Good info, mine is a 95 and only air dryer problem I have had was faulty relief valve that caused lack of air pressure. Rebuild kit solved that. Thanks for being so thorough in your explanation.
Gary B
Barry,
After reading what BJ has went through I have some more info to add.
This all transpired after I retired so it took a call or two to get some more info. They had a problem with the some of the E series compressors causing the AD-9 dryers to rapid cycle. My friend sent me a link to the bulletin that addresses this problem and may be of some help to someone that has an AD-9 that has a fast cycle. http://www.bendixvrc.com/itemDisplay.asp?documentID=5425 (http://www.bendixvrc.com/itemDisplay.asp?documentID=5425)
He also said that to stop the same type of problem with the Pure Air Plus that they done some porting and added that little valve that you have a question about. At this time it is not a user serviceable item. Understand that this could change tomorrow. If they ever offer it, it would most likely be in the DQ 6020 lower repair kit. To make things simpler in the future the DA 33200 may be all that will be available as it will work in all applications. Even with this upgraded dryer you still need the isolation valve.
Barry, As I understand it your compressor/governor will never know the difference.
Pamela & Mike
Relative to the Haldex air dryer part numbers, I believe the DA 33100 is still the current replacement for the original Midland-Grau N4250. The DA33200 was built to work with the type E compressors and has the isolation valve built into it and so does not require an external isolation valve. At least that's the way mine is installed, so I hope that's right.
BJ,
Great write up. This doesn't apply to my coach but appreciate the technical contribution. You deserve several karma points for it.
Rick
Mike & Pamela, I was under our coach today and noticed a metal tag on our reman air dryer:
Haldex-Midland
Part # DA33100X
0511
Remanuf
Thanks for your help. . .
Just finished replacing the air dryer in our 2003 with a remanufactured Haldex-Midland Part # DA33100X. We have always done the service kits as required but this time we decided to swap out the old unit since it was really due for a full rebuild.
We picked up the part at our local Napa for $264 + $99 core charge (I will get the core charge back tomorrow). Looking at the old unit it was certainly time for a rebuild / reman unit.
We did not have that valve on our dryer either.