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Air Dryer

I've had an ongoing problem with excessive oil spitting out of the air dryer ever since I got my coach 3 years ago.  It is a 1998 U320 with M11 engine.  Cummins told me it had to be a bad compressor leaking oil around the rings so I replaced that twice during that period.  It seemed to help initially but both times came back within 4 or 5 hundred miles.  I recently took it in again and a Cummins mechanic finally figured out that it needs an Econ, or isolation, valve.  An Econ valve is required on an air dryer when used with a Holset Type E  air compressor.  Apparently its function is to pressurize the discharge line when the compressor is unloaded.  From a Bendix tech tip: "The E Type Compressor requires air pressure redirected to the head when the governor cuts out or in the unloaded mode, if the wrong Air Dryer is used, excessive oil passage may occur causing premature component failures".  According to Foretravel, when it left the factory it had a Midland-Grau (now Haldex-Midland) Pure Air Plus, which I believe probably had an integrated Econ valve.  When I got it, it had a Meritor-Wabco installed with no Econ valve.  Don't have the maintenance history so I don't know when or how that happened. 
I decided I would rather replace the dryer than add an isolation valve.  The new successor model to the Pure Air Plus is the Haldex PURest DA34200.  Turns out it is too big to fit and would have to be moved over with a lot of rework to the mounting.  So now I am looking for another replacement that would drop more easily in where the old one is.  Possibilities are:
Meritor-Wabco 1200 series, which I think is a newer version of what I have now, but I have not been able to find a model advertised that has an integrated Econ valve
Haldex-Midland Pure Air Plus DA33200, successor (I think) to the N4250 that was supposed to be in it originally, so hopefully would fit.  Not a current model, may only be available as rebuilt
Bendix of some flavor.  Don't know anything about these.
So I'm looking for comments/suggestions/experiences (good or bad) any of you have relative to these air dryers.
Thanks
BJ Holden
BJ Holden
'98 U320 36'
Motorcade #16754

Re: Air Dryer

Reply #1 –
Would seem the method Foretravel had set it up origionaly worked fine until some one decided to "improve" the system.
For me, I would be going back to the Foretravel setup, like the rest of us are using with no issues, Parts fit and work properly.
FWIW

Re: Air Dryer

Reply #2 –
Pure Air Plus are readily available rebuilt...
The selected media item is not currently available. Dave Head & Megan Westbrook
Titusville, FL - The Great Outdoors
'98 270 buying this month
Toad is a 2018 F150 XLT

Re: Air Dryer

Reply #3 –
BJ,

See if this posting I made last year helps. I saw an add-on brass fitting on the large air hose on the side of the dryer that had a valve inside. Maybe that is why we have that mystery valve. Can a call to Foretravel Parts expert Mike Grimes may shed some light on your situation? I am also copying a reply to my posting. Sorry to see this problem is still around and it looks like it is not from too much oil.

Barry & Cindy

Previously posted by Barry & Cindy:
A month ago, our Haldex Pure Air Plus air dryer bottom purge valve stuck open after we parked in a campsite during leveling. We did not have air pressure to our wet tank, but were in a great place to be stuck.

We have changed the desiccant & coalescing filter many times using the DQ6026 service kit over the years but have never rebuilt the 15-year old bottom valves. We do carry the inexpensive DQ6020 Lower Housing Repair kit, but decided to not rebuild our air dryer ourselves at this time.

We purchased a complete Haldex part number DA33100X remanufactured Pure Air Plus air dryer with new desiccant & coalescing filters at NAPA for $234. Top filter kit and bottom repair kit is about $135, so the reman unit cost about $100 and looks like new. NAPA list is $310 for the part.

Standard Haldex connections shows a small hose at control port from governor, large hose from air compressor to input port and a large hose from output port to wet tank. Foretravel has added a brass check valve with four hose connections to the air dryer input port: 1) from compressor, 2) to dryer input. It seems when compressor stops compressing, this check valve connects 3) compressor air line to dryer control port which also has the governor connection. There is also a 4) small nylon brake line from check valve to wet tank. Foretravel air schematic drawing shows the air line from control port to input port and also the plastic #60 air line from input port to wet tank. On our coach the #60 plastic air line was clogged up.

Does anyone know why this check valve is added by Foretravel and how the check valve works?

We removed all original brass fittings from original dryer, cleaned them up and put everything back together on reman dryer with thread sealer on the pipe threads. Everthing checked out with no air leaks and we are good to go

again. Old air dryer had a $99 core charge.

Barry,

On ours the #60 line has a check valve that is made into the 90 where it comes out of the wet tank. It is a pain to get to, to remove and clean. The check valve that you speak of at the dryer sounds like the same set up we have. Did you take it apart and clean the piston bore and install 2 new "O" rings?

If you take it apart you will see that it is a balance piston that operates the check valve and not a spring. If the piston is not free in the bore then the valve will operate slow. If the "O" rings are bad then you can have an internal air leak that is impossible to find because the air escapes through the dryer inlet.

On our air schematic it didn't show the #60 line or the line from the control port. It would have been a big help if it had been there (we had to pencil ours in like drawn as built) when we first had a problem with our air dryer. Now it is old hat.
Hope this is some help

Pamela & Mike

Re: Air Dryer

Reply #4 –
Hi Barry
Yes I think the brass part you describe is an isolation valve.  Here is the Haldex reference for it

Haldex

See if that looks familiar.  You can also find it on Amazon (KN23500).  When I check the Haldex Pure Air Plus part numbers I find that the DA33100X that you installed does not have an integrated Econ valve so it would need to have an add-on somewhere or you would probably be spitting oil too.  The DA33200 is the model that has the integrated Econ valve, so if I go that route that is what I would try to get.  I found it very interesting that the reply from Pamela&Mike in your posting said that they had the valve installed down by the wet tank.  I wonder what year their coach is.
I think I will call FOT and try to find someone who can explain all this stuff -  Do we all have Cummins/Holset Type E compressors and do we all have/need isoloation valves?  If so what air dryer/isolation valve combinations have they used through the years and where have they put these things?  Have they switched over to using integrated isolation/econ valves and what model air dryer did they switch to?  If I was with the gang over in Quartzsite right now and had a lot of coaches to look at I could probably figure these things out, but right now I don't even have my own. 
I will have them check the bolt hole patterns on the mounting plate on Monday to verify that it looks like a Pure Air Plus was originally in there. If so I would prefer to go back to that but I don't know how much plumbing (line lengths and fittings) might have been changed when the Wabco was installed. 
Still mystified why it was ever changed.  Found a reference to a recall on N4250's in 1994 but that should have been resolved by the time mine was built in 1998.  But probably whoever changed it out didn't understand the isolation valve issue and it got left off when the Wabco was put in. 
BJ Holden
'98 U320 36'
Motorcade #16754

Re: Air Dryer

Reply #5 –
BJ,

That is very interesting that you identified the mystery brass part that I could not find information on.

When I 'accidently' turned part 'A' in your isolation valve drawing, I saw O-rings and springs. I just tighten it back up and left it alone. I originally thought it was just a 4-way connector.

The replacement air dryer I got from NAPA had a brass a 'something' that looked removable, into a hole in the bottom of the air dryer. The top of the 'something' was flush with bottom of dryer and did not stick out like the pressure release valve.

Our original dryer just had a plug in that same space. Contacting Haldex was no use to identify that 'something' part. Maybe it was an isolation valve. I will add a photo of the air dryer parts.

Barry

Re: Air Dryer

Reply #6 –
That brass valve is the overpressure relief valve
previous 1984 35 ft ORED 250 HP 3208 Cat       
previous 1998 40 ft U295 CAI 325 hp Cummins
previous 2003 40 Ft u320 build #6140 450 Cummins M11.                                                         
1999 Mazda Miata
Ron, Nancy, Tipper the cat, Max The dog
1997 U 270 36 ft build number 5174 8.3 Cummins
 

Re: Air Dryer

Reply #7 –
Isn't the over pressure relief valve the sideways brass valve that you can completely see all sides?

My mystery valve is the brass valve that we can only see the top of the valve as the complete valve is in a hole with top level with bottom of the air dryer.

Anyone know what this valve is? Is it another overpressure relief valve?