Another Brake Relay Valve - Updated again

[Tenor]

I'm sorry Zubzub!  I misread your post!  At least though, I can say that with all 6 lines clamped, it STILL exhausts out the bottom!  AAAAAAARRRRRRGGGHHHHH!  I've got a new inversion valve I'm going to jam in now. 

Glenn

[robertglines1]

not being familiar with the 7  I had a 78 8 MCI a few years back...does that system use a double ck valve?? just trying to reason system thru..doesn't make sense it worked when you first installed and 2nd one did same thing. will look to see if I have system diagram later...hope you get the gremlin..

[zubzub]

No Problem, I probably wasn't clear enough. Before installing another valve, maybe bench test it first.  over the years I have managed to collect quite a few bits and pieces as I am sure you have.  After installing the wrong brake valve on my bus with out bench testing, the next time I checked everything out with some shop air and a bunch of air lines etc....made sure I understood how to hook it up.  Your problem is weird though, plus I don't have DD3s so I can't take you far in that.  But basically look at the air diagram for the system and reproduce it at the relay on your bench..
Since this is a DD3 is it possible you have a separate anti compounding valve or is that just for spring brakes (like I said DD3 I know nothing)?
Next suggestion is also DD3 ignorant but is it possible the  parking brake valve in the cockpit is malfunctioning?

[Tenor]

Thanks Zub!  I have a stack of fittings that I can try.

Bob, I'd appreciate any help you can give.  I have the schematics, but they don't get detailed enough and they don't show flow.

I put in the new inversion valve.  (That job stinks!) and the brake relay valve STILL leaks!  At least I know where the problem is not. 

Glenn

[bevans6]

Perusing the schematic for my bus, 1980 vintage MCI, there is no interconnection between the inversion valve and the relay valve.  the relay valve is connected to a supply - the dry tank - with two lines, to the pair of service brake chambers, one line each, and a signal line to the treadle valve.  The reason it is there in the first place is two-fold - one, to ensure an adequate supply of air to each rear service chamber, which is why it's connected directly to the dry tank, and second - to reduce the lag time to apply the rear brakes.  The signal line doesn't move any volume of air, just sends a signal pressure, so reacts far faster than filling and stabilizing pressure to the brake chambers all the way from the front of the bus.

I would say that if you remove the two lines to the service brake chambers and plug those ports, and it still leaks, next  close off the supply lines from the dry tank one at a time, to see if the leak is common or isolated to one supply only.  After that, remove both supply lines and see if just the signal line causes a leak.  After that, try a flotation test...

Brian

[robertglines1]

basic brakes..set in seat release parking brake;this sends air to parking brake to release them also pressurizes the ck valve in brake relay valve to prevent air from being dumped out..(if this system is not maintaining pressure against ck valve it is not then closed)..so if you apply shop air to the port that is attached to the parking brake release connection .:and it stops..the problem is in the can..

[bevans6]

Robert, that's how it works for spring brake systems like you have, OP has a '68 MCI so I am presuming early DD3 system.  The parking brake system is separate from the service brake system on the DD3.  Releasing the push-pull valve to take off the parking brake applies pressure to the lock port on the DD3 via the inversion valve, and releases pressure, if there is any left, at the parking/emergency brake port, but does nothing related to the relay valve. A full service brake application actually upsets the locking mechanism and releases the parking brake.

When you apply the parking brake on the DD3 system, actuating the push-pull valve exhausts the air in the line to the inversion valve, removing pressure at the lock port of the DD3 and applying a regulated 85 psi pressure to the parking brake port.  That applies the brake and locks it on.  No need to also make a service brake application to "set" the brake,in fact the Bendix literature recommends against it although you can't compound the DD3 like you can the spring brake chamber.

Brian

[Tenor]

OK, I think I've got it.  If I'm right, I'm an idiot!  After talking with Robert Glines, I realized that there was no air going to the top of the piston to relase air to the brake cans during service brake applications..  It looks like I was able to move the airline from the brake treadle valve from the top of the relay valve to the  bottom (ie. outlet side) of the relay valve.  So every time you hit the brake pedal, it just dumps the air from the treadle valve right out the bottom.  I'll get this changed in a little while and report back just exactly how stupid I am...  Thanks to everyone for their help and PATIENCE!

Glenn

[robertglines1]

Brian Could he have the wrong rely for the old system or will the r-14 work on his system...what we discussed is how the r-12 or r-14 worked as far as internal operation and ck valve operation(internal) he did say the brake arm on the wheel never moved when his wife pressed pedal..I hope a lite went on and he figured it out...its hard to help when you can't lay hands on problem..but we all try and I know people help me figure out solutions daily..Bob....I think he has it...

[bevans6]

Robert, my bus with it's DD3 system has an R8 valve and my expectation was that his did too.  i think there is a big opportunity for some errors to be made if converting to a later valve.  I think Glenn has it, or is on track to it - the signal line from the treadle valve appears to be exhausting directly out, and it shouldn't do that.  It should dead-end at the relay  valve and is exhausted by the same quick  release valve  that exhausts the front brake chambers.  So my expectation is that the signal line from the front is connected to the wrong port on the new relay valve.

I enjoy the mental exercise of diagnosing what is going on, and I like to help people out anyway, so it's all good, particularly if the problem gets fixed!

Brian

[Tenor]

FIXED!  So the original brake release valve's top half side port is labeled "DRAIN ONLY", yet that IS the input for for the signal line from the brake treadle valve.  The new valve has the same port, but it is labeled "SERVICE" and it is a smaller opening.  I read that to mean "this is where you SERVICE the valve, not "this is where the SERVICE brake line goes".  Again, thanks to everyone for the help!

Glenn

[robertglines1]

you are now the expert on these valves.....trial by fire.....good job ! Bob

[bevans6]

On my air brake course the instructor mentioned that line is often a smaller diameter line to improve the reaction time to apply the rear brakes.  smaller line, less volume of air.  Maybe that is why the port was smaller?

good job well done, congrats for not giving up!

Brian