Bendix Air Brake School review

[rv_safetyman]

I wanted to let the board know about the Bendix Air Brake School and what a great training class that it turned out to be.

I am the type of person who wants to know as much about the various bus systems as possible – especially the safety related systems .

The school is three days long and cost $200 which includes great reference materials and three hot lunches – quite a bargain!  The details for the class are at:

http://www.bendix.com/learning/AirbrakeSchool.do

The class is aimed at folks who work on air brake systems.  The material is presented in a useful format as opposed to huge amounts of theory.  I have studied air brake systems for several years, but really did not appreciate the basic concepts.

I would recommend the class to anyone wanting to learn more about their air brake systems.

We did preview a new training CD that Bendix has been working on for a couple years.  It is a bit more basic than the course, but should be exactly what bus folks might want if they want to know more about their systems and how to test them.  The CD will be available to Bendix dealers and industry trades folks first and then to the general public.  It is scheduled to be released in the next couple of months and will cost $50.  It is very structured in the implementation and at the conclusion of the training, you can send a file that the program generates (based on your tests) to Bendix and they will send you a certificate.  I have been involved with developing computer based training in the past, and this implementation is, by far, the best I have seen. 

One last comment, the training permitted me to re-plumb my troublesome parking brake system so that it no longer needs the service brake application to release the parking brake (i.e. it now functions like the standard truck brake system).

[Len Silva]

Here is one of the best sources I have found for air brakes.

http://www.bendix.com/downloads/air_brake_handbook/BW5057_online.pdf

Len Silva

[rv_safetyman]

Hi Len.  Good point.  This handbook has been my bible for many years.  The book is a part of the course handout.

Section 9 contains 5 different tests that each bus owner should perform at least once a year.  They are simple to do, but will tell you if the system is working properly.

A couple of comments based on the class and some other research.

The test in the book says the the system should build from 85 to 100 PSI in 40 seconds with the engine running at high idle.  Our buses have at least one extra tank for all of the accessories  and the build time will probably be over 40 seconds. 

The issue of oil in the wet (and primary/secondary) tanks is often of concern.  Remember that the compressor is designed to pass a bit of oil to lubricate the upper part of the compressor.  Bendix has a special test which includes a special catch container and a chart that relates amount of collected oil to the drain period.  Since we don't use our buses every day, "Kentucky Windage" would have to be applied.  The test is described in a trouble shooting guide:

http://www.bendix.com/downloads/BW1971.pdf

[JackConrad]

Jim,
    I am interested in the procedure to replumb the parking brake.  Jack

[NCbob]

Amen to replumbing the parking brake.  I'd love to relocate my parking brake valve to the dash or side panel.

NCbob

[rv_safetyman]

Hi Jack.

I think that you have DD3 brakes (as opposed to a straight spring brake).  My Eagle has straight spring brakes.  

The modifications I made, would probably be unique to the Eagle system.  That system has a special valve arrangement that combines a set of valves (SV-1 and a special version of a DC-4) that create the interlock that requires the service brake application.  I removed those valves and made a direct connection of the two lines connecting to this valve combination [from the PP-1 (parking brake application valve) to the SR-1 (inversion valve)].  There are a couple of other plumbing issues but this is the major change.

[JackConrad]

Thanks Jim,
    You are correct, I do haave the DD3 system. I thought that is what you had on your Eagle. Well, see what happens when I think LOL.  Jack

[Chuck Newman]

Hi Jim,

I'm looking for a system that will cut off the braking air to my towed (M&G System)
in the event the coiled hose breaks for any reason.  I looked into the tractor protection
valve but it appeared to not be exactly what I need.  It was designed for tractor/trailer
combos with dual air feeds.

In your experience, have you thought about the need for a simple and quick automatic
air shut off to the towed?

Thanks,

Chuck

[rv_safetyman]

Hi Chuck. 

I have also been concerned about this kind of application. 

I pull several lines off of the wet tank for various things such as the fan clutch, range shift on the transmission and the air to the towed brakes.

First of all, it is probably not the best practice to pull these things off of the wet tank, since it is the “dirtiest” tank in the system.  However, I have a very good air dryer, my compressor is new, and I drain the tank often.

Now to the question at hand.  I have to assume you are concerned about loosing braking air if you break an accessory line.

There are two options.  We could pull the type of applications I mentioned above off of the accessory tank.  With the check valves, that would protect the primary and secondary tanks.  However, my accessory tank is in the front of the bus and it would be a pain to plumb back to the rear of the bus.  Also, a large leak could really drop the system pressure.

The second, and best option, is to use a Bendix PR-4 (or PR-2) pressure protection valve.  This valve will close at a preset value (most common values are 70 and 85 PSI).  This valve would have the supply side plumbed to the wet tank (or tank of your choice) and the delivery side plumbed to your accessories.  If any of the accessories have a large air leak, the valve would close at the preset value when the system pressure drops and preserve the system at the preset value so that you would have sufficient pressure for breaking. 

The main issue here is that you would need to watch your gauges to note that you were having quick pressure drops (should do that anyway).  If you ignored the gauges, you would have a functioning system, but the compressor would be working way beyond its duty cycle (25%).  This could cause compressor problems and the dryer would not work well since it would have to purge much more often than it is designed for.  However, these two problems would occur in even greater magnitudes without the PR-4 valve.

[Chuck Newman]

Jim,

I agree except I won't be using constant pressure tank air.  I will be using "proportional braking" air
from the area of the R-12 valve (page 2 of Bendix Air Brake Manual).  Where ever I can find a
convenient tie in.
Air pressure to the towed will be zero until brakes in bus are applied. 

I was looking at building a circuit that would sense the brake light signal, then also sense air pressure at
the quick connect port to the towed.  The problem with that is normal braking pressure can run
anywhere from a very few PSI to 40 PSI or more.  And I can't put a check valve in the line
because the M&G air cylinder needs to bleed down with the bus brake air when the brake pedal is
released.

My intuition tells me I am trying to redesign the wheel here, when in fact there is a simple fix.
Anyone with the M&G system ever address this potential problem?

Thanks.

[rv_safetyman]

Chuck, I am not sure why you would need anything connnected to the brake light switch.

As far as the R-12, it has an exhaust port, so you could simply use one of the delivery ports and hook the M&G to it.  When the signal from the E-6 opens the R-12 it will activate the bus brake chambers and M&G piston with a pressure proportional to the foot pressure.  That is the installation they show on their website.

If you want to isolate the towed brakes, you could connect the delivery port of the bus R-12 (or a tee off of the E-6 signal to the R-12) to signal port of another relay valve who has the supply input from the protection valve I discussed before.

I am probably missising something here.