Bruce,

Thank you for being so understanding and patient.

It is safe to assume that the air pump was running often. Probably not continous but very often. I rebuilt my air dryer the part of the year and was amazed at how it works. The biggest villian is this white milky sludge that is caused by a mixture of air/water/oil. The pop off can get "stuck" because of the build up. In Bruces case, his pop off was stuck closed. In my case it would stick partially open. The air pump is a mechinical pump that is virtually impossible to wear out. I would imagine that if you looked at that air dryer in Bruces bus you would have found the sludge, it is just a natural by-product of drying air.

I will try to locate a .pdf of the "plumbing" for hte AFO and post it this afternoon. Basically, the AFO tank is "spliced" into one the feed lines to the bus air tanks with the flow protection valve on the input side of the tank. The treadle air is spliced in the 3/8 air line that goes between the quick release valve (e-brake) and the service brake relay assembly.

Here is how it works:

When you park the air is removed from the chambers which allows the spring to fully apply the brake (i.e. park brake). When you release the brake, air is allowed into the chambers which pushes the spring off. When you apply the treadle, air must be removed from the spring brake side of the chamber while at the same time being allowed into the service brake side. This is rather difficult to picture in your mind but a fairly simple process.

To be as safe as possible using the air on the bus, we tap in after the bus service air but before the e-brake air, if that makes sense. This is metered air but the service brakes have already used it so brake timing from front to rear is not changed more than one or two pounds. If we simply grabbed the air from the service relay as many do, brake timing from front to rear would be changed drastically. Brake timing is the time that passes between the front brakes coming on and the rear. If the timing is changed too much abnormal wear can occur on the fronts since the rears are delayed by a lack of air.

By adding the AFO tank and relay assembly, brake timing is preserved and catastrophic events are avoided.

I hope this helps you understand the system. I will look for the .pfd after church.

Pete