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This video was made in 1967 by the US Army, but the information still applies today, some 42 years later. It is 24 1/2 minutes long, well worth the time if you want to understand the air brake system in your bus or truck.

Air Brakes - Principles of Operation (http://www.youtube.com/watch?v=qJa5-_ExsBE&feature=related#normal)

Now do you mean to tell me that you'd believe a video that is almost as old as I am?
;D  BK  ;D

If we consider when air brakes were really put into service-there operation has been basically the same since WWII.  This was a good video-too bad that the spring or Maxi parking brakes were not discussed. 

When air discs are started to be used, everything will be the same except that the air chambers are activating the disc brake.  Course now the new trucks and buses have ABS on them-which is a modulating relay valve with an additional electric solenoid in it so the brakes can be released electrically through the ABS circuit to prevent brake lockup.

The next generation of brakes will not have the air lines at all going to the relay valves.  Instead, the brake pedal will be an electric rheostat that regulates the electrical pulse going to the individual electric relay valves at each axle.  This will decrease the application time to the brakes making air brakes feel more like car brakes without the lag between pushing the brake pedal and applying the brakes.  Personally-this system makes me a bit nervous since if there is an electrical problem-no brakes.  Our current braking system, with the change over to air discs, is a very reliable system.  Good Luck, TomC

Thanks Paul ;D

Very good video, Thank you, Paul

BTW...you can see it in full screen view by right click on screen and left click on Watch on You Tube. Then after the You Tube page is open... left click on full screen icon at lower right corner

Sojourn for Christ, Gerald

thanks for posting that...cleared up a few things for me !