fbpx

Cart

The cart is empty

Cannot find your purchased courses? Click here to Login!

From a mechanical standpoint, modern air brake systems are unlikely to fail.


Air Brakes Won’t Fail | Air Brake Smart

https://youtu.be/c1ldt8qK-HM

Updated Jan 2021

Closed Caption


Introduction

Hi there smart drivers Rick with Smart Drive Test talking to you today about why air brakes won't fail.

In the last decade, we have equipped vehicles that carry our most precious cargo with air brakes.

And if air brakes failed they wouldn't be on those vehicles.

In the last two decades improvements in technology and the increased numbers of fail-safes on air brakes have more or less made these bulletproof.

The only failing of an airbrake system in this day and age is brake fade, and drivers have to work pretty hard to experience brake fade on an airbrake equipped vehicle.

Stick around to the end of the video, and we'll tell you which vehicles carry our most precious cargo.

PASS CDL Air Brakes First Time - take this comprehensive course!
A course for truck, bus & RV drivers operating a vehicle fitted with air brakes.
This self-paced course gives you:

• more than 100 practice test questions with feedback;
• EASY step-by-step instructions how to conduct a pre-trip inspection on an air brake system;
• DETAILED rules to use air brakes and brake downhill with a large vehicle safely;
• step-by-step instructions and precise wording for pre-trip inspection of trailers with airbrakes;
• explained SIMPLY to you is the tractor protection system and its components.


 Illustrations, checklists, & cheat sheets ensure your success 

Cart and Checkout


[OPENING CREDITS & MUSIC]

Hi there smart drivers, welcome back Rick with Smart Drive Test talking to you today about why air brakes won't fail.

As part of the requirement in both the United States and in Canada and other parts of the world, drivers have to take an airbrake course.

In those airbrake courses that were developed in the 1970s, many drivers are taught that air brakes are dangerous.

And that air brakes could potentially fail at any given time.

Unfortunately that is no longer true!

With advances in technology, modern air brake systems are more or less bulletproof.

And I would argue that the time has come for a revamp of all of these airbrake courses, because drivers do not need to know the technical inner workings of an airbrake system.

So what we're going to do today, we're going to go over why air brakes in this day and age are unlikely to fail.

Air Tanks (Air Reservoirs)

First failsafe of the airbrake system that will prevent it from failing are the air tanks themselves.

The air tanks on these systems are capable of holding enough air for 6 to 12 full brake applications.

So if the entire system shuts down, there's still enough volume of air in those air tanks to make 6 to 12 full brake applications and to stop a fully-loaded commercial vehicle equipped with air brakes.

You don't need a full brake application to bring the vehicle to a stop, so there's plenty of air in those tanks that if the compressor falls off the side of the motor or the whole system shuts down, there's still enough air to bring that vehicle to a stop.

One Way Check Valves

The one-way check valves at the entrance to the primary and secondary systems are the next failsafe on the system.

These prevent air from bleeding out of the system in the event there is a system failure or a break in the line between the compressor and the air tanks.

So the air can only move one way through the system.

It's unlikely, that if the compressor stops working or the main discharge line is broken, the air is going to bleed out of the system because of those one-way check valves which prevent the air from coming back through the system.

It only goes forward in the system.

Dual Air Brake System

The one-way check valves lead us into the next system and this system is found not only on air brake systems, but on your personal vehicle as well.

All braking systems are divided into two independent subsystems: if one system fails, the other will continue to work normally so long as the air compressor continues to pump air, which is rare that the air compressor will fail.

Even on a hydraulic system on your passenger vehicle, if you open the cover off of the master cylinder, you will see two chambers in there.

Since the late 1960s, all hydraulic braking systems have been divided into two independent subsystems - one for the front, and one for the rear.

An airbrake system is the same, it is divided it into two independent subsystems: the secondary, and the primary.

The secondary runs the steer axles and the primary runs everything behind the driver.

And it is the most prominent fail-safe system of an airbrake system, but there are more.

The air compressor on an air brake equipped vehicle provides ample air to operate the air brakes, but also the many accessories on the vehicle.Air Compressor

The air compressor is another failsafe on the system.

These air compressors pump more air than could possibly be required and we see that on modern air brake systems because the air compressor pumps enough air to run all of the air accessories on the vehicle, whether it's a bus or a truck.

And one of the most demanding systems that uses air pressure is the air-ride suspension, because unlike a passenger vehicle that has airbags and it is just a balloon that you pump up and it just pushes down like as if you were going to squish a balloon.

On a tractor trailer or a bus there is air constantly being evacuated out of the airbag system when it goes over a bump, it actually releases some of the air and then it fills back up.

The compressor is constantly pumping air to fill that air ride suspension.

As well as other accessories on the vehicle: air ride seats, or in the rare case of windshield wipers, gear selectors and those types of things.

The air pressure is used for a lot of other accessories, so the air compressor is another failsafe on the airbrake system because it can supply enough air to not only run the air brakes, but all of the accessories on the vehicle.

Pressure Protection Valve

The next failsafe--saying that about air accessories on the vehicle--there is a pressure protection valve on the system.

So what happens is, if the system pressure starts to drop between 60 and 90 pounds (psi - pounds per square inch) the pressure protection valve will shut off air to the accessories and direct air just into the air brakes.

So that's another failsafe, is the pressure protection valve which redirects air from the accessories into the air brakes if there's a loss of air pressure between 60 and 90 pounds.

And it varies a little bit depending on what vehicle you're operating.

Low Air Warning

One of the most prominent fail-safes on a modern airbrake system is the low air warning device.

And in this day and age, they're all a light and a buzzer - so they're audible and they're visual - you can see it and hear it.

And the low air warning is pretty annoying - it's that, you know, most annoying sound in the world.

[MAKING BUZZER SOUND & CHUCKLING]

That sound -we all know that sound! Man that's annoying!

The low air warning comes on at 60 pounds and the reason it comes on at 60 pounds is because at 60 pounds there isn't enough air pressure in the system to hold the gigantic springs off in the caged position which activate the parking brakes and also work as the emergency brake.

So at 60 pounds the low air warning comes on.

Sound

And in keeping with the low air warning, all of the air pressure on an airbrake equipped vehicle is plumbed through the dash and even over the sound of all of the road noise, and the diesel engine, and people talking--if you're driving a bus, driving a truck--you can hear air leaks on that system.

So even a minor air leak is prominent and you will be able to hear it.

So that's another failsafe, is that the driver is actually paying attention to the vehicle and listening to what's going on and hearing air leaks in the system.

The yellow parking control valve on the dash applies and releasing the spring brakes on the truck or bus.Spring Brakes

The most prominent failsafe on the airbrake system, next to the dual air brake system-- the division of the system into two independent subsystems--are the spring brakes.

Most of the time the spring brakes are used for parking, but in the event of an emergency and there's a loss of air the spring brakes are going to activate because while the vehicle is going up and down the road, those giant springs are held in the released position by air pressure.

And unlike the movie Terminator, which can see here in the clip when he rips the air tank off the bottom of the bus and they lose the brakes, that will never happen on a real airbrake system.

What happens is that you lose all the air pressure in the system, the springs expand, and engage the brakes.

So most of the time those spring brakes are used for parking, but in the event of a catastrophic air loss in the system, the spring brakes will engage and the vehicle will come to a screeching halt.

And oftentimes that happens between 20 and 45 pounds per square inch.

So if you're the driver and that low air warning comes on and you're not paying attention--and usually what I say to drivers is that you have to be sleeping, stoned, and really drunk not to hear that air loss or hear the low air warning and not know that it's going down between 20 and 45 psi.

Because if you don't pay attention, you are going to be doing a bug impression on the inside of the windshield because that vehicle is going to come to a screeching halt!


In-Cab CDL Air Brake Checklist This checklist will ensure that you know the numbers and pass your CDL Air Brake In-Cab Pretrip Inspection first time!

* FEAR :: Correct procedures for the MUST-DO IN-CAB CDL AIR BRAKE INSPECTION;

* SELF-CONFIDENCE :: Detailed sample test shows you how the tests are completed step-by-step;

* EMPOWERMENT :: Easy to use guide cuts through all the rigamarole of CDL manuals.

Get Your Driver's Test Checklist Now!


Tractor Protection System

The next failsafe on a truck designed to pull trailers with air brakes is the tractor protection system.

The tractor protection system as it's called--this is one of those that the engineers actually got right.

The tractor protection system protects the tractors air supply in the event that the trailer falls off the back of the truck.

Just quickly the tractor protection system consists of two valves:

1) the trailer air supply valve on the dash and

2) the tractor protection valve which is called the same thing as the track protection system just to confuse drivers when we're teaching it to them.

Anyway, the tractor protection valve in the back is kinda like the guard, it monitors air pressure into the trailer.

If it detects catastrophic air loss in the trailer, it'll tell the trailer air supply valve on the dash to shut off air to the trailer to protect the air supply in the truck.

It's another failsafe on 18 wheelers and trucks designed to pull trailers equipped with air brakes.

Automatic Slack Adjusters

[DRUMROLL] Drumroll...the last failing of an airbrake system was manual slack adjusters.

Manual slack adjusters had to be adjusted by the driver to keep air brake systems in adjustment and working properly.

And up until the mid-1990s and early 2000s, 75-80% of trucks during the annual blitz on the part of the CVSE (Commercial Vehicle Safety & Enforcement) the MTO (Ministry of Transportation of Ontario) and the DOT (Department of Transport) in the United States found that trucks were put out of service because brakes were out of adjustment.In the last 2 decades, air brakes have been fitted on school buses because these braking systems are reliable.

In the early 2000s, the province of Ontario, Canada did a study to look at vehicles going over the scales and looked at how many of those vehicles were equipped with automatic slack adjuster - so six years after it became law that automatic slack adjusters had to be fitted on new trucks and trailers and buses, they found that 96% of vehicles had automatic slack adjusters.

So here almost two decades plus years later most vehicles have automatic slack adjusters.

And actually, if they go into a shop for their annual inspection and are found to have manual slack adjusters they have to be swapped out, for that vehicle to pass its annual inspection.

Automatic slack adjusters are on most vehicles in this day and age...actually all vehicles in this day and age - they won't pass their annual inspection.

Automatic slack adjusters are reliable and work well to keep the brakes in adjustment.

And as I said, manual slack adjusters were the last failing of the airbrake system.

And essentially automatic slack adjusters are just a ratchet mechanism that when the brakes are applied it clicks over to the next ratchet position.

It's kind of like a boat ratchet....click, click, click...and when the brakes wear and there's a certain amount of slack and the pushrod comes out of the brake chamber a certain distance, it will ratchet over to the next position and keep the brake adjustment.

And these are effective - quite effective actually.

They've made air brakes almost more or less bulletproof.

It was the last hole in the air brake system that has now been corrected.

Conclusion

And finally, the "proof in the pudding" of why air brakes are more or less bulletproof in this day and age.

In the last five to ten years, school buses, that carry our most precious cargo, have all been fitted with air brakes.

And air brakes are more or less bulletproof because they're on school buses.

Question for my smart drivers:

Have you taken an airbrake course in the last decade and were you taught to believe that air brakes would fail and we're not reliable?

Leave a comment down in the comment section, all helps us out.

Log in to comment
blog image

Brake Fade | Air Brakes

Author: Rick
Although air brakes are more-or-less buletproof these, like all braking systems, have one failing: BRAKE FADE.
Default Image

Two-way Check Valves

Author: Rick
Must be used whenever two sources of air are used to operate a single device or system. For CDL air brake test, the driver must know there are 2 in the system.
Default Image

Trailer Hand Control (Spike)

Author: Rick
OBSOLETE Independently applies and releases the trailer service brakes. Knowledge Test Question: This air brake control is not to be used for parking. Although most tractors are still equipped with hand valves, beyond a trailer service tug test, these air…
On most trucks, the air lines to the trailer are plumbed into the tractor protection valve.

Tractor Protection Valve

Author: Rick
The tractor protection valve protect the tractors air supply from being depleted in the event of a trailer breakaway.
Default Image

Stop Light Switch

Author: Rick
Activates the brake lights when a service brake application is made by the driver.
Default Image

Spring Parking Brake (Emergency)

Author: Rick
Applies the parking brakes of the air brake equipped vehicle indefinitely – if needed of course. The parking brakes are held in the “ON” position by the mechanical force of the springs; these spring parking brakes are held in the “OFF” position by system air…
Default Image

Spring Brake Modulator (Inversion) Valve

Author: Rick
OBSOLETE Used on some vehicles with dual air systems. This device provides a means of using the force of the spring brakes to assist in stopping a vehicle in an event of a failure in the rear (primary) air system.
Default Image

Slack Adjuster

Author: Rick
Slack adjusters have three purposes: 1) To convert the forward linear motion of the push rod into rotary motion of the camshaft. The slack adjuster works on exactly the same principle as a box end wrench on a nut. 2) To act as a lever, thus generating greater…
Default Image

Air Tanks (Reservoirs)

Author: Rick
Stores compressed air for braking and for other air operated accessories. The air tanks are the first fail-safe in the air brake system. In the unlikely event that the air compressor fell of the side of the engine, the air tanks (reservoirs) store enough air…
The relay valve takes a message from the brake pedal and draws air directly from the air tank to the brake chamber, thus reducing brake lag.

Relay Valve

Author: Rick
Several relay valve throughout the air brake system reduce brake lag, thus allowing the brakes to apply faster.
Default Image

Relay Emergency Valve

Author: Rick
OBSOLETE Fills the trailer air tanks (reservoir) and applies and releases the trailer service brakes. The relay emergency valve also applies the trailer emergency brakes in the event of a trailer breakaway or normal disconnect. Knowledge Test Question: In the…
After a brake application, air is exhausted from the air brake system via the quick release valve to reduce brake lag.

Quick Release Valve

Author: Rick
The quick release valve moves to reduce brake lag in the air brake system.
You must know what a manual front wheel limiting valve is for your CDL air brake test. These are no longer found on modern trucks.

Manual Front Wheel Limiting Valve

Author: Rick
OBSOLETE To reduce application pressure to the steering axle by 50 % compared to the drive axle brakes, when required by reduced road conditions (rain, snow or ice). The system consists of a dash switch with 2 positions: Dry Road: 100% front wheel braking; in…
Air Brakes Simply Explained is a comprehensive manual that guarantees that you will pass your air brake ticket first time.

Brake Pedal - Foot Valve OR Treadle Valve

Author: Rick
MUST KNOW The brake pedal applies the service brakes - truck, or truck and trailer brakes. In other words, the brake pedal brings the vehicle to a stop when it it depressed. SHOULD KNOW The foot valve operates the secondary and primary sub systems…
Default Image

Compounding Air Brakes

Author: Rick
OBSOLETE Making a heavy service brake application while the parking brakes are applied. This is often an error of truck driving school students.
A caging bolt is used to release the emergency brakes in the event of an emergency (life or death situation).

Caging Bolt

Author: Rick
Allows the spring brakes to be manually released in an emergency - a dire emergency.
Default Image

Brake Linings & Drums

Author: Rick
To stop the vehicle, brake linings rub against the brake drum. This action creates friction, converting the vehicle's forward energy of motion into heat energy, which stops the vehicle’s tires. If the tires have traction, the vehicle will come to a stop. The…
Brake fade is the only reason that a modern air brake system will fail.

Brake Fade

Author: Rick
Brake faide is the only reason that a modern air brake system will fail.
A bobtail proportioning valve will move most of the braking to the front steer axles when there's not trailer attached.

Bobtail Proportioning Valve

Author: Rick
A bobtail proportioning valve great increases braking safety owing to different weight distribution.
Default Image

Automatic Front Wheel Limiting Valve

Author: Rick
To reduce application pressure to the steering axle brakes during most braking situations. Reduced pressure to the steer axle brakes occurs for most braking applications. Only during hard braking is there equivalent pressure delivered to both the front and…
Default Image

Air Gauge(s)

Author: Rick
The gauges are in either pounds per square inch (psi) or Kilopascals (kPa). These measure the amount of air pressure in the primary and secondary air tanks.
Default Image

Air Brake Chambers

Author: Rick
Convert air pressure into a strong mechanical force to apply the foundation brakes.
The one-way check valve is primary responsible for the division of the air brake system into a primary and secondary sub-system.

One-Way Check Valves

Author: Rick
A cattle chute with one-way gates allows the cows to only move in one direction – forward. A one-way check valve in an air brake system works exactly the same – it allows air to only move in one direction – forward through the system. The one-way check valves…
air brake adjustment

Air Brake Manual Adjustment – Pry Bar Method

Author: Rick
Using the pry bar method, confirm that the brake is in fact out of adjustment. After confirming that the brake is out-of-adjustment and it is equipped with a manual slack adjuster, complete the following steps to bring the brake back into adjustment. If one…
Default Image

Compressor or Build-up Test (Air Brakes)

Author: Rick
Depending on which province you're in, the air buildup time or compressor test has somewhat different paramenters. Still, all require that the diesel motor be at a fast idle. A fast idle on a diesel engine is between 900 &1200 rpm.
Default Image

Pry Bar - Check Air Brake Adjustment

Author: Rick
The National Safety Code madates that every driver of a commercial vehicle equipped with air brakes must check push rod travel every day. In many jurisdications, drivers are allowed to use the pry bar method; in others , they must use the applied stroke…
Default Image

Applied Stroke - Check Air Brake Adjustment

Author: Rick
The National Safety Code madates that every driver of a commercial vehicle equipped with air brakes must check push rod travel every day as part of his/her pre-trip inspection. In some jurisdications, drivers must use the applied stroke method; in others, they…

© Smart Drive Test Inc. 2024.

Contact Us: [email protected]