00:00Have you ever stopped to think about how a truck loaded with dozens of tons can stop on a steep
00:07descent without the brakes failing?
00:11If you drive a passenger car, you probably never had to worry about that.
00:16But behind these huge vehicles, there is a braking system completely different from what's in your car.
00:24And understanding how it works can change the way you see everything that moves on the roads.
00:38Today we are going to talk about the air brake.
00:41That system that makes trucks, buses and heavy vehicles stop using nothing more than compressed air.
00:50If you've ever been next to a truck on the road and heard that characteristic sound of air being released
00:57when it stops, that's the air brake at work.
01:01But why do trucks use air instead of the hydraulic system that regular cars have?
01:07To begin with, we need to go back to the 19th century.
01:10In 1869, the American engineer named George Westinghouse invented the first air brake system for trains.
01:22At that time, stopping a train was a dangerous and unreliable process done by men who turned brake cranks manually
01:31on each car at the engineer's signal.
01:35Westinghouse realized that he could use compressed air to activate the brakes on all the cars simultaneously and patented an
01:45improved version of his system in 1872.
01:50His great innovation was not just using air, but creating a system that was fail-safe.
01:59Where, if the air tube broke or the train separated, the loss of pressure would cause the brakes to activate
02:07automatically.
02:09This prespo is the same one that governs air brakes to this day.
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02:43And how did this system make it into trucks?
02:47The Westinghouse Airbrake Company started adapting the air brake for road vehicles in 1921 and around 1921-1925.
03:00Air brakes were already standard equipment on heavy trucks in the United States.
03:06The principle was the same as the one invented for trains, adapted to road conditions.
03:11But then, why don't we just use the same brake system in cars?
03:17In passenger cars, the system is hydraulic.
03:21When you step on the pedal, you push fluid, which is the brake fluid, through tubes to the wheels.
03:28And that pressure makes the pads press the discs.
03:33The problem is that a loaded truck can weigh more than 40 tons, while a passenger car weighs, on average,
03:42about 1.5 tons.
03:45To generate enough braking force in such a heavy vehicle, using a hydraulic system, you would need an absurdly high
03:55fluid pressure,
03:56which would require much stronger pipes, hoses, and seals, increasing the risk of leaks.
04:04And here is a very critical point.
04:07If the hydraulic fluid leaks in the brake system, it runs out, and without fluid, you also lose your brakes.
04:16A train or a truck that lost brake fluid at high speed would become an out-of-control projectile.
04:24And that's where air comes in, as a solution.
04:27Air is an inexhaustible resource.
04:31If there's a leak in the air brake system, the compressor simply pumps more air in, maintaining the pressure.
04:39And there is no risk of running out of fluid.
04:42Besides, the air brake system has a safety mechanism that the hydraulic system can't replicate.
04:50It's designed to fail with the brakes engaged.
04:55But how exactly does the air brake work?
04:58The heart of the system is the air compressor, which is powered by the crux engine.
05:04This compressor pumps air into the reservoirs, where it is stored under pressure.
05:11A component called the governor controls when the compressor should pump air and when it should stop,
05:18keeping the pressure within a safe range, typically between 100 and 135 psi.
05:26A unit of pressure, that means pounds per square inch.
05:31When the driver steps on the brake pedal, he is not pushing fluid like in a car.
05:37He is opening a valve that lets the compressed air from the reservoirs flow to the brake chambers on each
05:46axle.
05:46These chambers have a flexible diaphragm.
05:50When the air arrives, it pushes the diaphragm, which in turn pushes.
05:55A rod that operates a NAS-shaped cam, which pushes the brake shoes against the drums on the wheels.
06:05It's the compressed air doing the heavy work and not the driver's foot.
06:10And what happens if the air runs out?
06:14That's one of the most important questions about the system.
06:18And the answer is, what makes the air brake so safe?
06:21The brake chambers or more than trucks have two sections.
06:26One for the service brake, which is the regular brake used while driving.
06:31And the other contains a powerful spring.
06:34That spring is always trying to push the brake shoes against the drums.
06:41During normal driving, compressed air keeps the spring compressed, keeping the brakes released.
06:47If the air pressure drops below a safe level for any reason, the spring overcomes the air pressure and the
06:56brakes are applied automatically.
06:59That's why when a truck is parked, it doesn't need a handbrake like a car.
07:03The driver simply shuts off the air system and the springs do the rest.
07:08The brakes are applied by default and it's the air that keeps them released, not the other way around.
07:17That means if the truck loses all air pressure in the middle of the road, it will stop.
07:24But it's strange to say that air brakes work so well, because there are several news reports saying that trucks
07:31lost their brakes and went looking for an escape ramp or using cars as bowling pins.
07:52When a truck is loaded or going down a steep hill and ends up using the brakes a lot to
07:59slow down, it overheats the brake linings or shoes and the drum itself.
08:05Something we call brake fade.
08:08When these elements overheat, it causes them to lose their ability to maintain friction and as a result, they can
08:17no longer hold back the loaded vehicle.
08:21But still, the compressed air system has a practical advantage that you might not have considered.
08:29Articulated trucks, those where the tractor unit pull set trailer need to connect and disconnect the brake systems between the
08:37two parts.
08:38With the hydraulic system, this would be a huge problem because it would mean connecting and disconnecting pressurized fluid lines
08:47with the risk of leaks and air entering the system, which compromises all the braking.
08:53With air brakes, you just need to connect the flexible hoses between the tractor and the trailer.
09:01The air that escapes during connection or disconnection is just air, not fluid that needs to be replaced.
09:11But the air brake system does, however, have limitations.
09:14It is more complex and requires more maintenance than the hydraulic system, with several components that need to be inspected
09:23regularly, such as the compressor, the governor, reservoirs, valves, air chambers and slack adjusters.
09:31Air also contains moisture, and if water accumulates in the reservoirs, it can freeze in cold regions and block the
09:40system.
09:41That's why, Kluks have automatic drain valves that drain the accumulated water.
09:48In addition, there is a response time between the pedal being pressed in the air reached in the farthest chambers,
09:57especially in very long vehicles,
10:00which is a factor that designers need to consider when sizing the system.
10:05The characteristic sounds you hear when a truck breaks, that hissing or whooshing sound, are the air escaping after braking.
10:15And the safety valves venting the excess pressure, ensuring that the system remains stable.
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10:51And you, have you ever noticed the sound of air when a truck stops next to you?
10:57Or have you ever wondered how such a heavy vehicle manages to stop in such a controlled way?
11:03Leave it here in the comments because I want to know.
11:05On the site, there are two interesting videos that you need to watch to expand your knowledge and explore your
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11:19That's it, engineering enthusiasts.
11:21Big hug, and I'll see you in the next video.
