Air brakes are standard in most heavy-duty vehicles running on highways. But why are air brakes used on heavy vehicles but not lighter ones like cars and bikes? Let’s find out the real reasons behind the use of Air brakes.
You must have experienced the loud hiss sound while travelling on a highway. These familiar sounds coming from trucks, trailers, buses, or any other giant vehicle can be annoying but is nothing more than a hissing sound from air brakes.
But did you ever think about why this happens when you apply brakes? Or do you ignore the sound believing it to be ordinary?
Whatever the case may be in your scenario, it is crucial to diagnose the reasons. This article covers everything regarding why the sound from air brakes is typical and their use on heavy vehicles.
We will also answer many questions such as the leakage limit of air braking systems, whether you require a license to drive an air braking vehicle and so on.
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Understanding The Difference Between Hydraulic Brakes And Air Brakes
Often used in small cars or other lighter vehicles, the hydraulic brakes typically use hydraulic fluid (oil or ethylene glycol) to stop the vehicle when you apply brakes. So, when you press the brake pedal, a force is generated inside the braking system.
The piston located against the brake pedal then moves inside the master cylinder. The hydraulic fluid beneath the master cylinder starts moving at sufficient pressure when this happens.
This hydraulic pressure, in turn, flows through wheel cylinders through a pipeline. As per Pascal’s law, the pressurized hydraulic fluid in the vehicle moves through all the four-wheel cylinders uniformly to apply brakes safely.
On the contrary, the air brakes work differently because the vehicle relies entirely on air. Typically, heavy-duty trucks, buses or trailers are equipped with air brakes to halt a vehicle smoothly and promptly.
The atmospheric air is filtered and then compressed through an air compressor in an air braking system. To maintain the compression, air pressure is maintained throughout the system by a governor.
When the compressed air reaches a certain pressure, the air compressor draws air inside the air storage tank through an airline pipe.
When you press the pedal, the air stored inside the tank travels within the enclosed lines to reach each vehicle’s wheel. Thereby reducing the speed and carefully stopping the rotating wheels.
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Why Are Air Brakes Safe For Commercial Vehicles?
Air brakes are a secure and straightforward medium to stop a moving vehicle. Commercial vehicles commonly use air brakes, particularly in context with two most important reasons: the heavy weight of the vehicle and the transported goods, and the convenience of air supply.
Generally speaking, heavy-duty trucks, trailers, buses, or even trains use air brakes to stop the vehicle because of the heavy load and extra effort required to apply brakes securely.
In simple terms, if you use hydraulic brakes in heavy-duty trucks, the heavy load of the vehicle makes it difficult to stop the truck at a safe distance. A driver may also face difficulties handling a heavy vehicle if a sudden fluid leak happens without a warning signal.
That is where air brakes in commercial vehicles demonstrate the ease and suitability to avoid severe accidents. Also known as emergency brakes, air brakes in truck-trailers, buses, or large cars are helpful as:
#1. Unlimited Air supply
Since air brakes use air to apply brakes, there are no problems such as fluid leaks, as in the case of hydraulic brakes. The air is constantly available and compressed at pressure, making it worthwhile for drivers to apply brakes, even at high speeds.
#2. Availability of Air Storage Tank
The air storage tank remains filled with air in an air braking mechanism. The air safety valve at the corner of this tank allows the air to move through an extended one-way pipeline towards each wheel. So, even if the compressor fails to operate, the air inside the storage tanks would stop the vehicle.
#3. Fail-safe Braking
The brakes in commercial vehicles or any other vehicle used for braking take a few seconds to work efficiently. For this reason, air brakes in these vehicles are integrated with spring brakes that come off as a rescue during emergencies.
#4. Keep the Engaging Brakes Open
A vehicle driven with air brakes keeps the engaging brakes open. That is to say, when you apply air brakes, you are reducing the air pressure and making way for air to release from the brakes.
#5. No problems of leaks and damage to the engine
There are several problems with hydraulic brakes – braking fluid can heat up and leak sometimes, causing damage to the braking system. Air brakes do not have leaks because they don’t use any fluids.
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Do Commercial Vehicles Require An Ideal Air Pressure to Operate The Brakes?
Yes, of course. With an Air compressor governor, air pressure in the air reservoir tank is often regulated. The governor mounted directly on the compressor controls the amount of air pressure stored in the tank.
As a rule of thumb, the governor sends a signal to the compressor to stop drawing air in the tank when the pressure reaches 120psi to 145psi. On the contrary, the governor also signals the compressor to pump more air when the pressure falls below 100psi.
How Difficult Is It To Maintain Air Brakes In Large Vehicles?
By now you know that air brakes use air as a medium to apply brakes. But the compressed air is a by-product of water and alcohol, and the combination of water and alcohol can dent the efficiency of the braking mechanism.
In simple terms, the air trapped inside the tank contains moisture that worsens during colder climates. Also, when ice builds up inside the tank during cold climates, it blocks the air from reaching across all the braking components.
Precisely why, modern air tanks are now adjoined with draining valves that automatically drain the moisture, water or alcohol-based solutions from the air. Although if valves are not present, you should ensure to drain the tank manually.
What Is The Maximum Leakage Rate For An Air Braking System?
For the best control of the vehicle, a mechanic would always recommend testing the air pressure before driving. However, if leakage still happens, the air leaks should always be more than 5psi in 2 minutes.
In certain circumstances, when the air leaks exceed 5psi, it is best to check the air pressure to avoid accidents and tire damage.
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How Effective Are Air Braking System In Terms Of Their Total Cost?
Air brakes are the safest and most efficient option for heavier vehicles. Known as an alternative to hydraulic brakes, air brakes are more robust and store high energy when compared to hydraulic brakes.
Hence, the reason why heavier vehicles use air brakes for smooth braking. In terms of its cost, air brakes tend to be $500 more costly than the cost of hydraulic brakes.
Air brakes, inclusive of repair and maintenance costs, will surely make you dig a hole in your pockets because of maintenance costs and replacements.
Are Air Brakes Convenient For Every Vehicle Type?
Air brakes are pretty safe for heavier vehicles like heavy-duty trucks, truck-trailers, buses, heavy-duty cars, etc. With the extra weight of these vehicles’ load, stopping a vehicle becomes the utmost priority.
And since air brakes are powerful to exert force on these vehicles, they are much more reliable than hydraulic for commercial vehicles.
However, for non-commercial vehicles like cars, air brakes can be a bit slow to operate. Braking fluid transmits the riders brake pedal push almost instantly to the wheels, whereas air brakes need a bit of time to bring in the stoppage.
For a 4000 pound car driving at 100mph, a delay of even 2 seconds to brake would mean disaster. Heavier vehicles however do not move at these speeds, and therefore air brakes are perfectly safe for them.
Do You Require A Commercial Driving Licence For Driving Air-braking Vehicles?
A commercial driving licence is a legal permit in the United States, allowing drivers to obtain special training and licence before driving an air-braking vehicle.
The requirement of a commercial driving licence depends on the vehicle’s weight. If the commercial vehicle weight rating (CVWR) of an air-braking vehicle exceeds 26,001 lbs, the need for a commercial licence becomes an absolute necessity.
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Frequently Asked Questions
#1. Are air brakes better than hydraulic ones?
Hydraulic brakes are likely to lose their efficiency due to leakage or failure of the braking system. In the case of air brakes, drivers feel safe and secure as the brakes remain engaged, and the constant supply of air generates more power to apply brakes in trucks or heavy cars.
#2. Why do heavy trucks use air brakes instead of hydraulic brakes?
Using hydraulic brakes in heavy trucks is a lot riskier, especially in unexpected fluid leaks or loss of energy. On the other hand, air brakes contain constant and unlimited air. So, even if air leaks, it will not cause failure in the entire braking system.
#3. How do air brakes work on big trucks?
Air brakes use air as an operating fuel to apply brakes in a vehicle. A compressor then pressurizes the compressed air, ultimately pushing air inside the air storage tank. When the air inside the tank reaches optimum pressure, the air finds its way toward the brakes at each vehicle’s wheel.
#4. Why are disc brakes not valuable for heavy trucks?
Disc brakes are not valuable for heavy trucks as they are more noisy, expensive, and require extra clamping force and power booster.
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A Few Final Words
Now that you are familiar with the importance of air brakes, you are also accustomed to their use on commercial vehicles. Despite the speed and accuracy that comes with hydraulic brakes, mechanics often recommend using air brakes for heavy vehicles.
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Thank you for reading the article, we hope that we covered every question that you wanted answered. If you still have doubts in the great debate on air brakes vs disc and drum brakes, we are here to help you win the argument every time!