Compressed Air Systems

[TommyL]

Ivan K. Mine is 1/2 in. Pipe threads in dryer so   I put a street 90 on inlet line regular 90 on outlet screwed together first . Lots of better ways but is what I had in stock. If I new how to send pictures I would.maybe wife can.

[96 EVO]

23 minutes ago, TommyL said:

  Hope lm not overlooking something thinking it’s the dryer.  

Well, there is one other thing.

There will be a pressure protection valve on one of your tanks (probably secondary) that allows 10psi of secondary tank and wet tank air, flow back to the dryer after the compressor unloads, to dry out the desiccant beads. This is controlled by the dryer regeneration valve.

When I replaced my dryer, this replacement PPV came in the kit. I purchased a knockoff dryer.

I don't know if Meritor/Wabco includes this PPV with their replacement dryers.

This isn't saying this valve on your tank is malfunctioning! Mine wasn't and the new replacement is sitting in my spare parts bin, but, it must fail often enough for these air dryer companies to throw it in!

Edited March 28, 2022 by 96 EVO

[Bill R]

15 hours ago, 96 EVO said:

There will be a pressure protection valve on one of your tanks (probably secondary) that allows 10psi of secondary tank and wet tank air, flow back to the dryer after the compressor unloads, to dry out the desiccant beads.

Tommy

I am not sure your system is like this, but on my system I have a charging valve that controls the regeneration of the Air Dryer (see pic below), https://www.wabco-customercentre.com/catalog/en/4341001240 , as described by 96 EVO.  I went ahead and replaced mine because these can wear out over time (22 yrs), but it may not be obvious that they are not working as designed.  My understanding is that if this valve is working correctly it should allow a brief charge back (10 psi) to purge the Air Dryer when the system reaches about 130 psi, but not allow any further backflow to maintain around 120 psi.  The sealing off of the valve to prevent backflow is what most likely will partially fail over the years (this will not show up by spraying the valve with soapy water).  So even if your Air Dryer is leaking somewhere, this valve should isolate the Air Dryer from the secondary tanks and not allow any pressure drop beyond the initial 10 psi drop.  It should also isolate the secondary tanks from the wet tank and air dryer when the compressor is off.

While the compressor is running you should hear a brief purge of air when the tank gauges reaches 130 psi and notice on the gauges the pressure drop around 10 psi.

As suggested you may want to replace this valve if this is how your system is designed.

 

[Chuck B 2004 Windsor]

When I was at the Diamond Hill Monaco repair facility, they checked my entire air system for leaks.  Ended up the leak was on the back side of the emergency brake push button.  Chuck B 2004 Windsor

[96 EVO]

3 hours ago, Bill R said:

Tommy

I am not sure your system is like this, but on my system I have a charging valve that controls the regeneration of the Air Dryer (see pic below), https://www.wabco-customercentre.com/catalog/en/4341001240 , as described by 96 EVO.  I went ahead and replaced mine because these can wear out over time (22 yrs), but it may not be obvious that they are not working as designed.  

 

Yeah, if this valve had failed, I'm not sure it would show up with the air dryer bypassed.

[vanwill52]

As Chuck said, the parking brake valve can be a problem.  In my case, the valve itself leaked.  I replaced it with a Chinese knock-off.  It lasted about one year.  Replaced that one with a Wabco (maybe Hadley?) eight years ago...no problem since then.

My greatest leak came from the treadle valve (air equivalent of a master cylinder).  I THINK the leak was actually coming from the connections and not the valve itself, but it was such a gymnastic feat to get to it that I replaced the treadle valve itself.  I think the connections were actually where the air loss was coming from because (as was typical of Monaco) all the lines were a tad short, so they did not exit each fitting straight, but were already being pulled to one side.  I bought new lines and fittings.  These were all the Push-to-Connect PTC type.  I replaced all the PPV (pressure protection valves) at the same time, as one of them had a very small leak.

Before the changes, I would go from 120 PSI to 30 PSI in a little over an hour.  Now, it takes over a week to leak down to 60 PSI.

With PTC fittings, it is VITALLY important that you have enough hose that they can exit STRAIGHT from the fitting.  They may seal even if they are in a bind, but will eventually stretch the O-ring and begin leaking.  Cut the ends of the hoses clean and straight with a razor blade.

[TommyL]

Bill R  just put new dryer on lost about 2# in1hr that’s ok in my world.My regen. Check valve .pressure relief are all made on the dryer.  Check valve on old dryer must have been bad. I pressured the outlet and it leaked from inlet. Will  look for more leaks and valves later. Thanks 

[96 EVO]

2 hours ago, TommyL said:

Bill R  just put new dryer on lost about 2# in1hr that’s ok in my world.My regen. Check valve .pressure relief are all made on the dryer.  Check valve on old dryer must have been bad. I pressured the outlet and it leaked from inlet. Will  look for more leaks and valves later. Thanks 

Good to hear!

Did your new dryer come with a new pressure protection valve?

[TommyL]

Just a new dryer, haven’t seen anything like Bill R post under there yet .

[jacwjames]

I replaced a part like that (I think) on my  rear tank, it was called a pressure control valve.  https://www.wabco-customercentre.com/catalog/en_US/4341003100

It is listed as part of the air dryer kit.  I replaced this along with any other part that had rubber type components that could degrade/fail over time when I went through my compressed air system. 

I did not go through my air dryer other then previously changed the cartridge, which I've done every 3 years. 

[96 EVO]

3 hours ago, TommyL said:

Just a new dryer, haven’t seen anything like Bill R post under there yet .

If you click on Jim's link, you will get a better view of what it looks like.

The photo above is looking straight up at the valve.

[Bill R]

6 hours ago, TommyL said:

Just a new dryer, haven’t seen anything like Bill R post under there yet .

Tommy - The part I posted is the same as James has posted.  Sorry I don't have a better pic.  It is what WABCO calls the charging valve.  On my system, on top of the wet tank there is the 5/8" line coming from the Dryer, and on the same connection a 5/8" line going back to the secondary tank.  By following the  5/8" line back to the secondary tank, the 5/8" line will go through the charging valve before entering the secondary tank.  As 96EVO mentioned, bypassing the dryer would not show a problem with the charging valve.

I am glad you were able to fix the quick leak down.  It appears that there was some sort of leak on the dryer system, but independent of that, your secondary tanks should not have lost pressure from a leaking dryer if the charging valve was working.

All that said, I would try to find the charging valve and replace it as it seems suspect in your scenario.  Most air leak problems are a combination of several issues.

[dandick66]

I’m trying to better understand exactly how this valve works.

My understanding is that once the pressure builds up (in my case 128 PSI), the governor cuts off the compressor and this valve allows the air in the tank to back flow for a 10 PSI drop.  My system drops the 10 PSI in about 30 seconds, but it continues to drop probably 1 PSI every 15 seconds.  When it drops another 10 PSI, the compressor kicks in and the cycle starts all over.

Looking at the WABCO website description of this valve, it says the valve allows back flow equivalent to a .015 diameter orifice for pressures greater than 110 PSI and .05 diameter orifice for pressures greater than 105 PSI.  There is no back flow for pressures below 90 PSI.  What I don’t understand is how it gets the 10 PSI drop.  Unless I’m missing something, the valve will allow the back flow all the way down to 90 PSI.  

[96 EVO]

2 hours ago, dandick66 said:

  but it continues to drop probably 1 PSI every 15 seconds.  When it drops another 10 PSI, the compressor kicks in and the cycle starts all over.

 

This is parked with no brake use?

[jacwjames]

3 hours ago, dandick66 said:

Looking at the WABCO website description of this valve, it says the valve allows back flow equivalent to a .015 diameter orifice for pressures greater than 110 PSI and .05 diameter orifice for pressures greater than 105 PSI.  There is no back flow for pressures below 90 PSI.  What I don’t understand is how it gets the 10 PSI drop.  Unless I’m missing something, the valve will allow the back flow all the way down to 90 PSI.  

When I was working on my compressed air leaks I took the PPV's apart, all the springs were corroded, but the PPV has a vent hole allowing air with moisture to come in.  They were also oriented wrong so any moisture that got in through the vent stayed. 

When I took this valve off I took it apart, it is of similar design as the ppv in that it has a large spring with a plate pushing against a diagram.  My guess is that the spring is what does the relief and once it gets down to a certain pressure it closes stopping air from releasing.   I could not see any problems with if but for ~$30 I changed it. 

As to your 1 psi drop every 15 seconds, my guess is you have other leaks.  All my PPV's were leaking, once I changed all of them along with new fittings and other parts my system stays up for weeks.

[dandick66]

3 hours ago, 96 EVO said:

This is parked with no brake use?

Yes, I’ve tried it with park brake applied and released, and service brake applied and released.  It doesn’t make any difference.

[96 EVO]

How well does your system hold air with the engine off?

[Romeo84]

curious if your unloader valve in your compressor is leaking, forcing your discharge line to stay open on your dryer. would be a steady leak. but not noticeably loud.

[dandick66]

58 minutes ago, 96 EVO said:

How well does your system hold air with the engine off?

It seems to drop the pressure whether the engine is running or not.  It drops to around 40 PSI overnight and drops to zero within 36 hours. I’ve also noticed a significant “squat” in the rear after the coach sits for over a couple of weeks without running.  I’m thinking this is a leak in the Valid leveling system or the rear air bags.  I’m going to start it up tomorrow and let it build pressure, then measure the rear height and see how quick it drops.

I think I’m going to tackle this in this order. 
1. Bypass dryer         
2. Replace charging valve.    
3. Remove and inspect/repair/replace PPV’s.

I’ll post my findings.

 

[96 EVO]

Is your dryer easy to access, or buried over your rear axle?

[Bill R]

Below are two documents for these systems and how they relate to the Charging Valve (Pressure Control Check Valve PCCV).   Maybe they might help.  They did for me.

There is a difference between the Charging Valve (PCCV) and the Pressure Protection Valves (PPV).   This is a link for the Pressure Protection Valves https://www.finditparts.com/products/1435318/midwest-truck-and-auto-wakn31000

The PPV opens at around 65psi and closes at around 50psi and isolates all air components except the brake spring relays so you have some residual pressure for the brakes should there be a rapid loss of pressure like a blown air bag. 

WABCO 1200 Maintenance Manual.pdf WABCO 1200 System Saver 1200 Installation.pdf

[dandick66]

39 minutes ago, 96 EVO said:

Is your dryer easy to access, or buried over your rear axle?

Dryer is very easy to access.  There is a door aft of the tag axle, driver side, that gives access to the AC condenser, air dryer and fuel filter/water separator.

14 minutes ago, Bill R said:

Below are two documents for these systems and how they relate to the Charging Valve (Pressure Control Check Valve PCCV).   Maybe they might help.  They did for me.

There is a difference between the Charging Valve (PCCV) and the Pressure Protection Valves (PPV).   This is a link for the Pressure Protection Valves https://www.finditparts.com/products/1435318/midwest-truck-and-auto-wakn31000

The PPV opens at around 65psi and closes at around 50psi and isolates all air components except the brake spring relays so you have some residual pressure for the brakes should there be a rapid loss of pressure like a blown air bag. 

WABCO 1200 Maintenance Manual.pdf 3.12 MB · 2 downloads WABCO 1200 System Saver 1200 Installation.pdf 273.23 kB · 2 downloads

Thanks for the documents.  I’ll look them over tonight.

 

[georgecederholm]

42 minutes ago, Bill R said:

Below are two documents for these systems and how they relate to the Charging Valve (Pressure Control Check Valve PCCV).   Maybe they might help.  They did for me.

There is a difference between the Charging Valve (PCCV) and the Pressure Protection Valves (PPV).   This is a link for the Pressure Protection Valves https://www.finditparts.com/products/1435318/midwest-truck-and-auto-wakn31000

The PPV opens at around 65psi and closes at around 50psi and isolates all air components except the brake spring relays so you have some residual pressure for the brakes should there be a rapid loss of pressure like a blown air bag. 

WABCO 1200 Maintenance Manual.pdf 3.12 MB · 2 downloads WABCO 1200 System Saver 1200 Installation.pdf 273.23 kB · 2 downloads

I've been chasing air leaks for a while and have been monitoring this thread. This is all awesome information. Since I'm dealing with a 2005 Exec (2004 build date), I'm thinking that I need to be planning on issues although I haven't been able to identify leaks with soap testing. I don't have air system diagrams but do have ones that Bill G surfaced years ago for a 2006 Dynasty (and up?) that should be similar. I think these documents are in this forum's "Files" section.

If I'm reading these diagrams correctly, I should have two PCCV (Monaco terminology "Check Valve 2-way Wabco #4106") and four PPV (Monaco terminology "Pressure Protection Valve 60# Wabco #4112").

Does this sound correct? I have a dryer assembly on order that supposedly has one PCCV, so I should source another. I'll probably source enough PPVs to replace all and have a couple as spares. Does this make sense?

I've been under quite a bit with soap spray and have cleared up most of the bubbles using new brass fittings and replacing push-to-connects with compression fittings*. I was focused on the bubbles and regret not taking pictures of all the tanks (2 primary and 2 "ping"), but will do so soon.

[jacwjames]

I was able to source everything pretty quickly from several different sources.   

I had 4 PPV but they were different in that in some cases the bottom ports were not operational, they were there but the holes were never drilled through.  There was one that used one of the bottom ports.  But what I found was that PPV were the same size and rated the same so I just bought all 4 the same and used the plugs that came with them to plug the holes. 

On the check valves I removed so I could get the numbers off, ordered and then installed when I got the new ones. 

I also replaced all the PTC fittings with new and kept the old ones as spare.  I had one 1/2 PTC that just wouldn't seal, the tubing was coming in at an angle so I just bought a compression type fitting and that solved the problem. 

I also replaced the pressure relief safety valve on the wet tank, I figured it was something that could fail, relatively cheap, so I replaced   BUT the thing was really stuck in the bung hole of the tank, I ended up breaking it off and had to cut/chisel it out and then use a die to chase the threads. 

 

[Bill R]

1 hour ago, georgecederholm said:

If I'm reading these diagrams correctly, I should have two PCCV (Monaco terminology "Check Valve 2-way Wabco #4106") and four PPV (Monaco terminology "Pressure Protection Valve 60# Wabco #4112")

George,

Each coach is different, but you should be able to identify your PPV's.   On my coach there are only three.  Two on the rear tank - one for two ride height controllers, and the other to the Hulsett Turbo Charger controller.  On the front tank there is only one for the Air Horn and front ride height controller.  Depending on how many Air System accessories other than the brakes will determine how many PPV's the coach has.  For example if yours has an air actuated step, my coach does not, you might have another one. 

My coach only has one 2-way check, Wabco 4106, which is now Haldex KN25080 https://www.haldex.com/en/na/valves-9c82abc0/check-valves/haldex-new/two-way-check-valve---shuttle-type/kn25080/

This 2 way check on my coach balances the pressure between the front and rear secondary (dry) tanks and supplies air to the brake spring relay.  This is to provide as much available pressure in both tanks for the brakes.

Neither of these is the Charging Valve (PCCV) for the Air Dryer.  If you can, trace the 5/8" line coming from the front wet tank going into the rear tank and see what it connects to before going into the tank and look for any type of Valve ID.  

It takes time and patience to trace lines, research and to check everything, and then you find something else.  And keep coming to this forum with questions.  I was helped tremendously by those in this forum like Jim J, 96 EVO, and many others.