Air brake issue

[Joseph Cummings]

5 hours ago, Jizzo17 said:

Yellow circle is the double check. Blue line feeds back to the relay valve which is circled in red. Red arrow feeds all the way to the cab through the firewall into the trailer emergency valve in the dash. Which is the one that is leaking out of the side when I push in the parking brake valve. But does not leak when I push the tractor park brake valve in. 

Try this. Connect the line from the dash valve straight through to the rubber hose going to the quick release valve mounted on the axle. Eliminate the valve you circled in yellow, just use a coupler. Clamp the line you highlighted in blue off with a pair of vise grips. See if your maxi's release and your service brakes work

[Geoff Weeks]

what is confusing me is saying the line from the dash is coming from the red (trailer supply) valve.  Either he is mixed up or the plumbing is mixed up.

 

"Red arrow feeds all the way to the cab through the firewall into the trailer emergency valve in the dash."

 

Otherwise it matches the Bendix diagram I posted on the bottom of the last page.

Edited Saturday at 11:25 PM by Geoff Weeks

[Joseph Cummings]

14 minutes ago, Geoff Weeks said:

what is confusing me is saying the line from the dash is coming from the red (trailer supply) valve.  Either he is mixed up or the plumbing is mixed up.

 

"Red arrow feeds all the way to the cab through the firewall into the trailer emergency valve in the dash."

 

Otherwise it matches the Bendix diagram I posted on the bottom of the last page.

So he hasn't even tested to see if the line coming from the dash valve is pressurizing when he pushes the knob in?

[Geoff Weeks]

Idk? This is one of those times when being there as seeing what is what will make all the difference

[Mark T]

Why is the double check  valve (shuttle valve) there ?  That's usually used to receive air from either a foot valve or a hand valve (trolly valve) . Did the same guy that didn't have any issue welding on the frame's flanges think he could use it to send air to two different places ?  Just for kicks, try gutting the check valve and see if all your issues go away. 

[Geoff Weeks]

10 minutes ago, Mark T said:

Why is the double check  valve (shuttle valve) there ? 

Anti-compounding

[Mark T]

Yes, but it doesn't belong there . Not on maxies

[Geoff Weeks]

yes it does, look at the last post on the previous page, straight from Bendix air brake manual.

[Mark T]

It's likely not working.

[Joseph Cummings]

You know how many old trucks I've seen converted from handbrake to Maxis without any kind of anti-compounding provision? Pretty much every conversion I've seen. And I've yet to see it break anything.

Anybody else remember the 55,000s with the rotochambers on them. You couldn't just bolt a 30/30 maxi on them without some mods

[Geoff Weeks]

None of this addresses why the parking brake is connected to the trailer air supply control?

[Mark T]

I think the picture on the last page is a schematic with what is sometimes referred to as an inversion valve. Another form of valve for anticompounding. That little guy in the picture is a shuttle valve. That's a valve like if on a truck there's a hand valve. So if air comes from the foot valve, that's one signal to the relay without bleeding back to the hand valve....or vise versa.  That little guy doesn't belong there. That post on the previous  page is a system with an inversion valve . It's deceiving because it's a generalized drawing. 

[Joseph Cummings]

2 minutes ago, Geoff Weeks said:

None of this addresses why the parking brake is connected to the trailer air supply control?

Yeah that would be a problem. How do we know this for sure? Somebody could have put a red knob on anything. I'd want a picture of the valves with the cover off the dash. God only knows what the kind of guy that welds to frame flanges might have done

[Mark T]

1 minute ago, Joseph Cummings said:

Yeah that would be a problem. How do we know this for sure? Somebody could have put a red knob on anything. I'd want a picture of the valves with the cover off the dash. God only knows what the kind of guy that welds to frame flanges might have done

I didn't wanna say that, but...

[Geoff Weeks]

We don't and can't from this end of the internet.  The double check may or may not be defective, but until the plumbing is sorted, anything is possible.

 Remember, when he bought it the spring brakes were backed off/caged.

It is likely that there is more than defective parts at issue here.

[Geoff Weeks]

11 hours ago, Mark T said:

I think the picture on the last page is a schematic with what is sometimes referred to as an inversion valve.

Listed right in the drawing as double check. An inversion valve is  different. They do completely different functions. An inversion valve has nothing to do with anti-compounding.

An inversion valve is used to modulate spring brake pressure in the event 1/2 of a duel system looses pressure. Many duel systems are plumbed so one rear brake is on one side and the other and the steer axle is on the other side. So a failure on the side carrying the steer axle would leave only 1 axle braked. If the spring brakes are placed on the side with the steer axle, the inversion valve exhausts spring brake pressure, applying the spring brake in coordination with the air pressure applied to the air pressure to the remaining axle. It provides more controlled emergency braking that slamming on the spring brakes.

Neither of my 9670's  had anti-compounding  nor inversion, but my Marmon has both. Often the anti-compounding and inversion are plumbed into a common duel function valve, because the inputs needed are the same, but the function of each is different.

An inversion becomes more important (mandatory) when a truck is used as a straight truck (like a tractor converted to a dump with the sleeper box removed). A loss of side of a loaded tractor, you'd still have trailer brakes plus one side at least of tractor brakes. It is never operated loaded without a trailer. A straight truck is loaded without a trailer and a single axle of brakes would not meet the emergency braking stopping distance call out the the reg's.

I don't know why some were fitting with anti-compounding and others were not, I just know that it happened.

[Mark T]

3 minutes ago, Geoff Weeks said:

Listed right in the drawing as double check. An inversion valve is  different. They do completely different functions. An inversion valve has nothing to do with anti-compounding.

An inversion valve is used to modulate spring brake pressure in the event 1/2 of a duel system looses pressure. Many duel systems are plumbed so one rear brake is on one side and the other and the steer axle is on the other side. So a failure on the side carrying the steer axle would leave only 1 axle braked. If the spring brakes are placed on the side with the steer axle, the inversion valve exhausts spring brake pressure, applying the spring brake in coordination with the air pressure applied to the air pressure to the remaining axle. It provides more controlled emergency braking that slamming on the spring brakes.

Neither of my 9670's  had anti-compounding  nor inversion, but my Marmon has both. Often the anti-compounding and inversion are plumbed into a common duel function valve, because the inputs needed are the same, but the function of each is different.

An inversion becomes more important (mandatory) when a truck is used as a straight truck (like a tractor converted to a dump with the sleeper box removed). A loss of side of a loaded tractor, you'd still have trailer brakes plus one side at least of tractor brakes. It is never operated loaded without a trailer. A straight truck is loaded without a trailer and a single axle of brakes would not meet the emergency braking stopping distance call out the the reg's.

I don't know why some were fitting with anti-compounding and others were not, I just know that it happened.

I might be calling it the wrong name, but there's that valve that interactas between the service and parking brakes. Some have that anodized steel cover on the top kinda triangle shaped.  The function of them is anti compounding. Depending the manufacturer they look a little different, but do the same thing.  That little valve in the picture is a double check valve. ( I've heard of them referred to as shutle valves )  That valve doesn't belong in that part of the system.  an anti compounding valve ???  well.... one could go there.  Believe it or not, I've seen this before. Guy will try using the double check valve as a manifold (?)  Parking brakes will work once or twice, then that's it. or maybe bleed off over a while, seem to work then back to not working.  It is a little confusing between differnt manufactures and different areas where guys (like me) tend to call things by the wrong name or a differnt name than what guys call them in a different part of the country.  Someone's got something plumbed incorrectly in that truck and it's not easy to call it via text and a few pictures.   🤔 someone mentioned that already

[Geoff Weeks]

Here is one form of the "all in one"/

Here is a Qr that acts as an anti-compounding as well

here is an inversion valve

Lastly there are the tractor spring brake valves that are Inversion and anti-compounding into one valve

[Geoff Weeks]

5 minutes ago, Mark T said:

I might be calling it the wrong name, but there's that valve that interactas between the service and parking brakes. Some have that anodized steel cover on the top kinda triangle shaped.  The function of them is anti compounding. Depending the manufacturer they look a little different, but do the same thing.  That little valve in the picture is a double check valve. ( I've heard of them referred to as shutle valves )  That valve doesn't belong in that part of the system.  an anti compounding valve ???  well.... one could go there.  Believe it or not, I've seen this before. Guy will try using the double check valve as a manifold (?)  Parking brakes will work once or twice, then that's it. or maybe bleed off over a while, seem to work then back to not working.  It is a little confusing between differnt manufactures and different areas where guys (like me) tend to call things by the wrong name or a differnt name than what guys call them in a different part of the country.  Someone's got something plumbed incorrectly in that truck and it's not easy to call it via text and a few pictures.   🤔 someone mentioned that already

This is right from the Bendix manual, so not me saying it. Yes a double check is used in some systems for anti compounding, it does the job and IS correct.

 Later as more valves like inversion were added, they move from a simple double check to a multi function valve. Some were QR/double check some were Inversion/anti compounding, but a double check was/is used for anti compounding.

[Geoff Weeks]

Here a link to the Bendix manual if you want to read through it yourself:

https://www.doverbrakeinc.com/downloads/catelogs/BENDIX AIR BRAKE HANDBOOK.pdf

It explains the use and names all the valves.

[Geoff Weeks]

In its simplest form, anti compounding just supplies the higher of the two air pressure supplies to the spring brake. So when the parking brake is off, system pressure is applied to the spring brake hold off chamber, but when the parking brake is on, there is no air supplied by the parking brake valve, so hold off chamber is empty. However if the parking brake is off, and the foot brake is applied, air will be supplied from the service system via the double check to the parking can and partially remove some spring pressure.

 A double check does just that function, it supplies the higher of the two inputs to the output.

Edited Sunday at 02:17 PM by Geoff Weeks

[Geoff Weeks]

To answer my own question on why some got anti-compounding and some did not, it seam the function, while helpful on trucks without auto slacks is required when auto slacks are used as the locking/self adjusting mechanism isn't as strong as it is on manual slacks.

 

Funny  those pushing for auto slacks never mentioned they were WEAKER! I never owned anything where they were required, my Marmon came close but before the deadline!

[Geoff Weeks]

Being that the temp is in the minus side of 0, I spent some time reading in the Bendix manual.

 With one exception, my Post -121 braked stuff all use the MV-2 multi function valve and is the most common layout used in commercial trucks.

Reading though the section of individual push pull valves, I think what we may have in the truck in this thread is the wrong valves being used for the function.

 The PP-3 and PP-7 look similar but differ in an important feature, The PP-8 should be the blue knob and can also be used on older trucks with a manual front axle limiting valve.

Most of the difference comes down to the automatic trip function and if it can be over-riden. The PP-3 system would require the blue knob to allow applying the tractor brakes only. The PP-7 will trip when the yellow tractor button is pulled but can be "overriden" or pushed back in to charge the trailer with the tractor brakes applied, this is also how the MV-2 system works.

 My pre -121 stuff is even more varied, as the cut-off function is in the TP valve (TP-2) on the back of the cab. The tractor parking has its own low pressure trip, but that doesn't effect the TP valve at all.

As the MV-2 and clones from other mfg were the most common, that is the one I am most well versed in. The few times I needed to change a PP valve I was sure to order by the tag and put the same type back in. I knew there were different types but till now never researched the differences.

I did wonder why the three button system existed, when the two button can be made to do the same (with the correct PP valve), but now I know.

The MV-2 is rebuild able, and very reliable, its biggest weakness is the rubber gasket getting soft and then leaking between the halves of the valve when the temp gets very cold, I think I still have one or two new rubber gaskets for the MV-2. 

[Joseph Cummings]

2 hours ago, Geoff Weeks said:

To answer my own question on why some got anti-compounding and some did not, it seam the function, while helpful on trucks without auto slacks is required when auto slacks are used as the locking/self adjusting mechanism isn't as strong as it is on manual slacks.

 

Funny  those pushing for auto slacks never mentioned they were WEAKER! I never owned anything where they were required, my Marmon came close but before the deadline!

I hate auto slacks. I've seen too many not function properly. I want to get under the truck at least once a week with a wrench and a grease gun and have a good look around. Grease is cheap and easy to install, much cheaper and easier than replacing parts

[Geoff Weeks]

I always was sure, after all the paperwork was done, after a level 1 inspection to point out the the inspector that 30 years after the auto slack mandate, brake problems were still the #1 equipment OOS fault, and my manuals passed! I just can't resist the dig!