Relay Valve or Inversion valve leaking

[Fredward]

To accomplish my drop box removal/reinstall I removed the driver's side DD3 because its in the way and the inversion valve because its attached to the drop box. Leaving all air lines connected, I just moved the DD3 and the inversion valve out of the way. Tonight I put it all back together and aired up the bus in order to retract the DD3 so I could attach it to the slack adjuster.

As the bus aired up, air started leaking out of the exhaust on the relay valve. When the bus is fully aired up air leaks from the relay valve exhaust when the parking brake is applied. When the parking brake is released for normal driving; no air leaking from the relay valve.

Should I look toward the inversion valve or the relay valve for the cause? It seems to me that the inversion valve must be bypassing air back to the service brake section of the DD3 which is leaking back to the relay valve and out the exhaust. The manual shows how to rebuild both valves. I'm guessing that moving the inversion valve around and tipping it on its side must have dislodged some crap thats making it stick ? It looks like the inversion valve you just take apart and clean and re-assemble.

Fred

[bevans6]

I wish I knew more about what the inversion valve actually does, but if you have air leaking from the service chamber to the QR on the relay valve when the parking brake is on, then I think it's probably a bad diaphragm in the DD3.  In my schematic, the inversion valve is connected to the "lock" section of the DD3, no pressure when locked as in when the parking brake is applied, and pressure when parking brake is released.  So no air is applied to the lock port to leak when parking brake is on.  it's also connected to the emergency brake chamber on the DD-3.  I don't see a path to the service chamber at all.

Air is applied to the emergency chamber when the parking brake is applied, and to the service chamber if you 'set' the brake with a brake application.  If you don't do a service brake application when putting the parking brake on, then air is only applied to the emergency brake chamber.  In either case, as soon as you release the service brake application, the QR on the relay valve operates and there should be no air pressure in the service brake chamber.  There will be pressure in the emergency brake chamber, at least until it leaks off, but there is no difference to the parking brake action, once it's on it stays on.

So if you have air continuing to leak from the R8 valve when the parking brake is on, then you have a leak between the emergency brake chamber and the service chamber on one of the DD3's.

I always 'set' the parking brake with a fairly full service brake application.  the Bendix data sheet recommends against this, it prefers that the parking brake be set with pressure on the auxiliary diaphragm only:

PARKING
The DD-3™ actuator parking function is activated by releasing
the air pressure from the lock port and making a brake
application. The application may well be made from the same
alternate source as used for the emergency application. It
should preferably be made on the auxiliary diaphragm for
reasons which will be explained under "releasing."
If the air application is released or leaks off, the shaft will
retract slightly and then be clamped by the wedging action
of the rollers. The brakes may now be considered to be
applied and to remain applied regardless of any exhaustion
of energy or loss of air pressure.
RELEASE OF PARKING APPLICATION
To release a parking application, air pressure in excess of
40 psi must be applied at the lock port and a brake application
slightly greater than the locked-in application must be made.
Thus if the park application is made with the auxiliary
diaphragm, an application of equal air pressure on the larger
area service diaphragm will provide the heavier application
required to free the lock rollers and release the park
application.

Document:  http://docs.google.com/viewer?a=v&q=cache:hK_OLBFoJrwJ:www.bendixvrc.com/itemDisplay.asp%3FdocumentID%3D2393+bendix+dd3&hl=en&gl=ca&pid=bl&srcid=ADGEESjjtjTEV8aJAAI6Kx5pAuJh8KCS2JA7B-DVcI87GtHTyzPUaRmR2cS6kbq2pMbPLft2OzMpKZ7x2SebpsAi0OBB6XHsGyK5oHWHl_jDkaAXFEAS4rpmmS06LNnFnkLoutUZQbXP&sig=AHIEtbQB6PEmimHmqUwnYTpQdBypKOuVyQ

Hope this helps, even a bit.  I also hope it's right...  just working from logic and data  sheets!

EDIT: thinking about this more, it's probably only half the story.  I do see a path from the inversion valve to the R8 valve through the shuttle valve.

Brian  

[robertglines1]

tap it with a rubber hammer..what ya got to loose...treat it like a Ford

[Fredward]

ITs strangely coincidental that this leak occured when I moved the inversion valve from the drop box and uninstalled the DD-3. Brian I appreciate the thoughts and schematic.

Bob, I tried tapping both items with a hammer. Looking in the manual, I see how to take each valve apart. One requires rebuilding and the other just requires cleaning.

Fred

[Just Dallas]

Removed

[Fredward]

Good Point Dallas. But I never disconnected them.
Doing a little more rooting around I think Brian is on the right track. I'm guessing the parking diaphram is leaking back through the service chamber and being exhausted out the Relay Valve exhaust. I might tackle this one myself or might take it in.
Fred

[Lin]

As you know, DD3 chambers are very expensive.  The best price I have seen on them is from REI, 800 489-9860.  I bought a compressor from them.  The man to speak to is JR.  He might be able to give you some needed info even if you do the rebuild yourself.  Since the DD3 cans are not seriously spring loaded, the rebuild may not be to bad.

[JackConrad]

I'm guessing the parking diaphram is leaking back through the service chamber and being exhausted out the Relay Valve exhaust. Fred

Fred,
  You can test this by clamping the parking brake hose to each DD3 (one at a time) to pinpoint the leaking diaphram.  Jack

[buswarrior]

Just typed it out the other day:

http://www.busnut.com/bbs/messages/11/35873.html?1273534907

With all the banging around, sounds like you forced its hand.


PS on edit, unless you have lots of time on your hands, with the price of new valves, versus the cost of a rebuild kit, the rest of the paid world just changes them out for fresh ones. No worries of rebuilding wrong, or not knowing the condition at which you should condemn your core.

happy coaching!
buswarrior

[Fredward]

Guys it was the parking diaphram. It had a hole in it.
Using shop air I extended the actuating rod all the way out; then removed the clamping rings one at a time, marking everything as I went. The parking diaphram was obviously bad. I changed the service diaphram as well. Put it back together; retracted the actuating rod, reinstalled and no more leak out the relay valve.  I've got a trip this weekend but after that I'll rebuild the other side. Everything else looked good. Although I think I'll replace the lines from the relay valve to the DD3. They seem OK but probably could stand replacing.

Very interesting project. Now I can get back to what I was doing; finalizing the drop box project. Just need to fill the differential and then put the newly balanced drive shaft back on.

Fred