Ok, here we go.

first I would like everyone to go to

http://www.icbc.com/licensing/lic_ut...commercial.asp

and get chapters 2, 7, and 8. You can download the entire manual but we will only be using those chapters.

This is the basis of my Air Brakes instructors manual, but I do not use it for everything. There are some things in that are actually wrong as you will see.

Lesson one. Back to the Basics.

Compressed air, the compressor, the governor and the wet tank.

Compressed air is air that has been forced into an area that is smaller than it would normally occupy at atmosperic pressure. A ballon would have about 1 PSI (pounds per square inch).

Most modern trucks operate with between 105 and 135 PSI.

What limits this is that you have a Governor attached to the compressor that has a built in limit. Almost always it is not adjustable and if the governor stops working, it is a replace and toss part.

A compressor is just like any engine, except that it does not generate power, it absorbs it. They are almost always attached to the engine and run with internal gears or chains. You can see on older equipment that they are sometimes stand alone parts that are spun with a pully system off of the engine and usually by belts. It is always best to carry an extra belt if you are driving something that old.

Chapter 7, page 158

You will see an example of an air compressor with the governor attached. I doubt the one in your unit will look anything like it.

How a compressor works is like this. A piston goes up and down, just like any engine. As the piston goes down, a valve opens and allows atmosperic pressure to enter the camber. When it gets to the bottom and starts its way back up, the valve closes and the air in the chamber is compressed into a smaller area. Once it gets to the top, another valve opens and the air flows to the Wet Tank. This just keeps going on and on, until a line that comes back from the wet tank to the governor gets to a certain preset pressure, then the govornor shuts down the flow of the air to the Wet Tank.

At that point, the Air Compressor does NOT shut down. It still keeps going up and down, but the air is not allowed to go to the tanks. It is either cycled between the cylinders, or vented in some way. (if someone knows of another way the air is prevented from going to the wet tank, please inform us)

As the air is used up, brake applications or small leaks, and the air gets to a certain preset point again, then the governor allows the air to go back to the Wet tank.

Usually, the air will start to reload about 20 PSI below the pre-set top pressure point, so if you had a 120 system, then it should recharge about 100, and if you had a 130 system, it should be 110.

Regardless, the minimum it should drop to is about 80 PSI. That is the law most places, and as you will see, your spring brakes will start to drag just below that.

We are going to use the term Maximum Reservoir Pressure often in this little course. Please remember it and what it is. It is the maximum amount of air pressure available for a brake application at any time. If you have two tanks, one has 120 psi, and the other has 125 psi, then MaX Res Pressure would be ......... 125.

Ok, so now you have a compressor and a govornor and a wet tank.

Go to page 159 and you will see a line going from the top of the Compressor to the top of the Wet Tank. This is how the air gets to the Wet tank from the compressor.

You will also notice a line that goes back from the Wet Tank to the Governor. This is how the governor knows when to shut down the air supply.

Please read pages 158 to 161.

I would suggest that you don't read ahead. We will get there in due time.

I am sure I am missing some important stuff, but bare with me as this is the first time I have tried to teach this way. Ask lots of questions, but try and keep them on topic. If it is something I will handle later in the course, I will tell you so and we will cover them then. Just remember your questions and we will get to them.

Also, lets really try and stay on topic and keep the stories to a minimum. We can always share them later. Also, remember this is a course on most systems and not specific ones. If you have a 1958 International R-180 that is different than what I am saying here, then that is great, bit it probably wont apply here, and as I said, it to specific to get into. I would need to be in front of the truck to see the issues it would have. Now, I would be willing to travel to see it, but you are going to have to float the cost for me to come there......

Questions and comments please.

 

First of all, thanks for taking the time to present this material.


On page 158, it states that the compressed air reaches temperatures above 204C or 400F.

I realize that gases rise in temp when compressed, but this seems very hot to me.

 

The numbers I use is when the air comes out of the Air Compressor the air will be about 400 psi and 400 degrees F.

The hot air, when it hits a cold tank, is what creates the mosture. This is why it is so critical to drain your tanks daily. This will be covered in the next lesson.

 

I used to have a fleet manager that didn't want us to bring the dump truck back to the shop with an air leak because he said the compressor would keep running and would ruin it. Any ideas on that? I thought he was a bit nuts at the time. :P

 

I would recommend NOT standing in front of trucks with brake issues ; )

 

Good safety tip. I will have to look at incorporating that into my class....