Why Do Big Trucks Use Air Brakes? How Does It work?
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- Опубликовано: 15 сен 2024
- In this video, we explore why big trucks use air brakes instead of the hydraulic brakes commonly found in cars. We dive into the mechanics of how air brakes work, the safety features that make them essential for heavy vehicles, and the importance of regular maintenance. From understanding the role of the air compressor to the critical function of the dual-circuit system, this video covers everything you need to know about the air brakes that keep these giants of the road safe.
Timestamps:
0:16 - Introduction
1:06 - The Need for Air Brakes
2:47 - How Air Brakes Work
5:02 - The Role of the Air Dryer and Safety Valves
6:13 - The Importance of Regular Maintenance
7:13 - Why Air Brakes Are Standard for Big Trucks
8:41 - Conclusion
#AirBrakes #TruckBrakes #HowAirBrakesWork #HeavyTrucks #TruckSafety #BrakingSystems #TruckMaintenance #SemiTruckBrakes #CommercialVehicles #TruckEngineering
I feel one of the key reasons air brakes are used was missed. It's the ability to readily attach the tractor's braking system to the trailer's braking system, simply by connecting air hoses together. Just like on a train, where the locomotive's braking system is easily attached to all the cars behind it. Imagine trying to that with hydraulics. Messy, inefficient, and not fail-safe.
One of my vivid memories of my teenage years was lying under my dad's semi at 2:00am in 20° weather trying to find a air leak.
As a truck driver, and mechanic. without even watching the video. I can tell you the reason why. It's because they're failsafe. Anything at all goes wrong with the brake system, and they lock on instead of just failing. Well then, you might ask why every car doesn't use them. They're marginally more complicated, require much more maintenance. Daily checks for leaks, and possible problems. As well as monitoring of various gages (and knowing what those gages mean, and the problems they're indicating). Asking the average person who doesn't even know how to check their own oil to do that? Yeah not going to happen.
Short answer....
The moment air brakes stop working is when they work best.
Another thing about air brakes is you can work on and replace any part of it, start the vehicle, wait for it to build air pressure, and then test the system. With hydraulic brakes, it is common to have to get someone to help you bleed the brakes. I find brake bleeding to be a time consuming process that is difficult with the configuration of the brake lines on some vehicles.
All of the smaller vehicles built after the sixties have duel circuit hydraulic brakes. Light and medium rigid tray trucks sometimes use an air over hydraulic system. The main reason large trucks use air brakes is for connecting the trailer brakes simply and easily, something that cannot be done with hydralics.
I never noticed the massive trucks sharing the road with me 0:19 🤣😭
Hello from Finland. Nice tutorial, thanks. Here our own trucks are in great condition due to mandatory yearly inspections (MOT) which are very strict. But Russian trucks are very often in really bad condition. Our Customs check Russian trucks when they arrive here. They must pass inspection before they are allowed to drive here. Often the driver loans or hires tools and fixes the problems themselves as they are used to maintain their cars even if it isn’t their own. And often they are much overweighted. Many trucks are turned back to Russia.
Interesting parallels with aviation here. Airliners use hydraulics (obviously), but like air brake systems, they use redundancies in a similar manner. Usually there are three systems that overlap, making failures of any given flight control or aircraft system very rare, and even if all three hydraulic systems fail, other methods provide pressure sufficient to safely operate the aircraft. In some smaller aircraft, the hydraulic pressure provides a fail-safe because landing gear is held up with the pressure, so any loss will result in the gear deploying to allow a safe landing. (In systems where this is not the case, there are numerous backup ways to drop the gear.)
They also use air brakes to scare automobile drivers next to them when stopped at a red light.
Holy crap! I’m about to start my fourth year of mechanical engineering undergrad. This channel is awesome!! It has the informativeness of those old discovery channel documentaries but with a modern flavor and quality. I’m glad channels like you exist :)
Air brakes main advantage is that it is not the driver’s muscles stopping the truck. An air brake pedal opens a valve and then air does all the work. You are not forcing fluid down a pipe with a plunger limited by your own strength. If you’ve ever had a trailer push you down a road you’d know that you may have to get up off the seat and stand on the pedal.
2:27 It should really be called air-released-spring-actuated-brakes. The air pressure is actually holding back the spring that when released would mechanically clamp the brake pads or press on the wheel drums to stop the spinning wheels.
When hydraulic brakes fail, they stop stopping. When air brakes fail, they stop not stopping. So air brakes are safer.
Big trucks and their trailers NOW have AIR DISK BRAKES ON ALL WHEELS, making the vehicle much easier to stop, and ABS to control skidding even on the trailers. This is the best safety system being installed on all trucks and trailers is long in coming.
Thank you for the knowledge. I'm from the Philippines. 🇵🇭 🇵🇭
Now that I think about it, using a hydraulic system would be problematic when changing out a trailer. If you introduce air bubbles into a hydraulic system, it would create a dangerously spongy pedal. When attaching the air connection through glad hands to link trailer with truck, a small amount of introduced air would cause no problem at all.
Air brakes can still function perfectly with a minor leak. The air brake system will never run out of air but a hydraulic system will run out of brake fluid if there was a leak even a minor one.
Interesting, diagram labelled a spring brake. But wasn't a spring brake chamber. Stated air brakes are used because of the safety of a spring brake chamber. Air brakes were in use prior to the introduction of the spring brake chamber.
As mentioned by someone else. Input (brake pedal) application pressure to actual available output pressure is much higher in an air brake system, as opposed to a hydralic system.
Yeah, that was a simple service brake with no emergency spring. Good catch!
To be fair, modern hydraulic system on cars and light trucks in a seen have two separate systems as well. Meaning if you lose fluid to the front brakes there is still a reservoir with fluid to control the rear’s and vise versa in case a failure. It will allow multiple petal applications to an extent on a dual master cylinder provided it doesn’t allow air to enter the piston area and back into the system that isn’t leaking.
Trucks use air brakes because long ago George Westinghouse designed and then proved they worked on railroad trains, significantly reducing train accidents.
I could simply say:
- hydraulic brakes use active pressure when pulling the brake lever
- air brake using passive pressure from the spring to press directly right on the rotor (with air regulator being managed by either pressing the lever or leaking by accident so the break will be applied right away
Great job !
I love learning.... subbed
The thing is on some trucks only one drive axle has the spring brakes so the other drive axle and the front brakes don't do anything if you loose pressure. It's more common for both drive axles to have springs though, but you're still not getting any help from the front. The front brakes really don't do much, but in an emergency the little bit they do will help a lot!! Normally all trailer brakes have springs so they will do some good. Springs can get worn and break over time and will never provide the same force as the air pressure operated part of the brake system even when new.
It stands to reason. Most of the braking effort is always on the wheels carrying the most weight. In cars, 70% of the braking effort is done by the front wheels because the front wheels carry 70% of the weight in most cases. In a truck the rear and trailer wheels carry the weight, so that is where the effort is generated. In Australia, where a majority of long-haul trucks have more than one trailer, braking systems are even more complex. Road trains in NSW and VIC include either two 40-foot trailers or a 40 footer and two 20 footers in a C-triple combination and road trains in other states and territories are often twice as long and can weigh over 200 tonnes (440,000lbs), depending on the load being carried.
All trucks built since at least the 80's have spring brakes on all drive axles, and all trailer brakes are spring brakes. Steer axles don't have the spring brakes because if the pressure drops too low, the spring brakes will activate on all axles. That's not good because locked-up steer wheels go in the direction they were last pointing - despite where the steering wheel is turned.
Can airbrake applied to small vehicles? Is it possible?
I see a channel called history of simple things, I subscribed.
one huge advantage is under hard braking you wont boil the brake fluid, and the air system and the valving allows for more pressure exerted to the brakes with minimal effort from the drivers foot and leg muscles.
It’s the way of the road boys way of the road.
A key feature that may have been overlooked is air brakes' ability to highly amplify the driver's pedal effort. Consider that typical automotive hydraulic brakes already use a ratio between master cylinder to caliper or wheel cylinder diameter to achieve some mechanical advantage, and pedal effort is amplified by a vacuum powered booster. On heavy trucks, compressed air acts directly on diaphragms at each wheel to perform this same function at much higher rates of amplification. It might be impossible to achieve the needed braking force if compressed air or some other similar motor pressurized fluid weren't used.
So thats the loud shwooshing sound when I'm near them. I thought they were suspension sounds.
How comes I never came across this channel?
Thanks for the clear explanation & nice graphics too. I suggest topic on solar energy & its important applications in today's world. 💯✌️👍
Hi! We'll try to cover that on our next video, but for now you can check this out :) ruclips.net/video/jneaauRjI8I/видео.htmlsi=MRXpn68seZJf3aA3
Personally, I think a de-pressurized system should have the brake pads spring-loaded into drum. That means the brakes are applied by default and require pressure to dis-engage.
I saw a truck stopping by a red light and I heard that air braking sound
Do you have a video of how the JAKE brakes work? 🚛
We don't. But we can try to cover this in our next video :)
Very complete video!
Great stuff!
theoretically they are great. but in reality most neglects to maintain the failsafe system. ive seen too many cases where trucks keep moving at insane speeds when the brake fails, instead of the failsafes (automatic engaging of brakes) deploying
Why did air brakes win out over vacuum brakes?
Skip to 2:20 thank me later
Im a lucky boy my mercedes vario has air over hydraulic, twice the fun!!
Big trucks use air brakes because the heat induced into the system by the massive friction it takes to slow a tractor hauling 80,000 lbs of goods would boil brake fluid in the lines and you would lose braking after the first few stops.
I always thought it was because disc brakes simply didn’t have the strength to stop that much momentum
So how come when a truck parks, there's always a huge rush of air releasing .
Interesting
Also, brake fluid tends to heat up and wouldn't be very useful going down steep grades.
Same system on trains by the way 🎉
Planes should have air brakes so they stop before hitting the ground.
Hydraulic brakes can be used so much that the fluid can actually boil, reducing effectiveness. That's why some mountain roads have Emergency Ramps for failed brakes, but they are rarely needed now.
1:15 Its better to use metric system values also in your videos. This will make everyone understand the content.❤
Thank you! We'll note this in our next videos :)
Hydraulic brakes don't "fail if there is even a single leak"
Just like air brakes, Hydraulic brakes are dual circuit. One circuit for front brakes and a completely separate circuit for rear brakes
You can make the fluid brake the same failsafe there is no difference, you can make a hydraulic brake default to locked.
yes i do wwtch these videos for entertainment purposes
Why not do a video on : "How does the gears work on a large truck ?"
It would be nice to see a video on how train brakes work.Ive studied them a bit and know they are actualy primitive and have no maxi,s as trains are much to long and it would take to much air to build up to keep all the maxi,s off and way to much time.I do know that if trains could have maxi,s there would be 45 people still alive in Lac Magontic Quebec.That horrible accident was caused because the train engeneer an other crew left it running up on the hill with the engine was running a to keep the brakes applied.There was some manual brakes applid but not enough.Unfortunately te train or engine caught fire ,the fire department arived and did what seemed to be the logical thing to do by shuting the engine off .However the air pressure drained off thus releasing the brakes and the hand brakes couldnt hold the train from starting to roll down the hill into town creating a horrible disaster.If the train could have had the same breaking system as tractor trailers then the engineer would have applied both the engine brakes and brakes on all the cars and the train would have stayed still if all the breaks or most of them were adjusted properly.
Air brakes began in the railroad industry, And for the same reasons.
so that is why big truck making that psssshhh sound when they are slowing down or stopping
Busses use the same air brake system, that's why trucks and busses don't move till the air pressure hits a safe release threshold.
My motor home has air brakes as it is based on a bus chassis. I had a valve failure in the dryer and had a hard time building up enough pressure to leave a RV site in the mountains in the thin air. When I got to a lower altitude the air was dense enough to overcome the leak.
I never kind of never knew that because really never thought of it as big trains trains have air brakes what when you think about is and does make sense a big truck like that, what about BIG jumbo jets when they land they might have air brakes as well I guess, thanks for the video😊
❤👍
This is why we have so many runaway big rigs?
Improper braking on the part of the driver, or neglected maintenance of the system.
Despite the effectiveness of the system, the driver must get the truck in the proper gear to control his speed before starting down a hill so the compression of the engine can assist the brakes, helping to keep the brake shoes from overheating. As the brakes heat up from the friction they apply to slow or stop the vehicle, the iron brake drum will expand, increasing the distance between it and the brake shoes and thus reducing the available force until they can cool back down. It's this reason why big diesel truck engines are equipped with a compression release braking system commonly known as the Jake Brake. The Jake operates by the use of an electric solenoid that briefly opens the exhaust valve as each cylinder begins its compression stroke, releasing the compressed air so that the piston must work against a vacuum, dragging it down and thus slowing the vehicle. The Jake is so effective that given a properly set up system, a skilled driver can bring the truck to nearly a complete stop by only downshifting the transmission as the Jake slows the engine to the bottom of its RPM range, only using the air brakes to make the final stop from a low speed. This technique keeps the brakes cool, ensuring they are there when needed for an emergency situation.
Same can be said for trains, they use vacuum or compressed air to operate brakes, giving the same fail safe advantage.
They were originally used on steam trains
It is a relief to hear this described correctly
Great video. But I hope you convert bound to kg unit
Almost all modern cars have dual-circuit design it's not something special...
Imagine some guy hooking his hydraulic lines for brakes for his trailer and had to bleed them every time you hooked and unhooked ?
if nobody invented air brakes yet !
What about planes?
The school bus I drove had air breaks. Air brakes work opposite than hydraulic. If there’s not enough air pressure, the brakes lock, stopping the vehicle. Thats basically how they work.
Quicker response. Compressed air moves at the speed of sound. Also if you tried to use hydraulics (fluid) to actuate all the brake chambers on a truck the driver would have to pump the brake pedal ten times to bring the brake shoes in contact with the drums.
hydraulique brake could do everything air brake do with less complexity the only reason air brake are still around in my opinion is because it would be hard to transition
Hydrauliques would be a big messy hassle when hooking trailers on and off. Something semi’s do daily !
Also air brakes are designed fail safe. If for some reason air pressure is lost (leak, hose unhooked, etc) the breaks would automatically apply on full force. Those trucks (and trains) need air pressure to release the breaks, not to stop.
If you car has a big leak you can’t stop. If a truck, bus or train has a big leak it is stuck and not moving
Imagine if the motorcycle was using air breaks.
And they cant make dual safety line in close line brake system? I believe why air brake still exist is a saving factor
The real reason they use air-brakes is the ability to change trailers; a hydraulic system would not allow for this. Air-brakes are archaic, it’s basically the same system that trains have used for over a hundred years.
Big trucks use air brakes to slow down and stop.
Still they are technically drum breaks
Why cant car maker add air break as its more safe?
If air brakes fail safe, then why do trucks lose their ability to stop when they are low on air? Try it, start rolling down a hill and keep applying and releasing the brakes until air is depleted, then try to stop.
By then the spring brakes will have engaged
They dont if the system is working properly. If you keep breaking and ignore the pressure warnings the brakes will slam on. Though if you keep braking on a steep hill, the brakes might overheat and that results in loosing the ability to stop (until they cooled down again)
Y air brakes won't won't f the engine stops🥺 hopes manufacturers get rid of it
Yeah that's why heavy vehicles crash so often by deny of breaking system
Air brakes let you drive off a cliff.
Easy connection of trailers is the real reason. The same reason trains use air brakes, albeit a completely different system.