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How Many Brakes Does a Semi-Truck Have?

How Many Brakes Does a Semi-Truck Have?

A high-quality braking system is essential to haul the heavy load in the trucks. Brakes in semi-trucks are different from the rest of the vehicles.

How Many Brakes Does a Semi-Truck Have? Semi-trucks have ten brakes on five axles, and all are air pressurized. They use compressed air to create pressure to slow down the truck. They are more powerful, safe, and reliable. The stopping distance of the air brake is usually 300 feet for trucks running at 55 mph. These trucks have 10 drums.

Proper working of the brakes is crucial for the safety of the driver, passengers, and vehicle. Any malfunction in the system can create a troublesome situation for the drivers. Regularly inspect them and fix all the faulty parts to avoid accidents.

Number of brakes in a semi-truck

The braking system is a crucial component of the vehicle. It is essential to slow down and stop the trucks and other vehicles. The number of brakes in each motor vehicle is different.

It depends upon the intended use vehicle size and the number of axles in the truck. A semi-truck is used to haul heavy objects from one place to another.

It is a big truck with 18 wheels and 5 axles. It has two brakes at each axle to slow down to stop the wheel beneath the axles. A semi-truck with 5 axles will have 10 brake assemblies attached to the axles.

A large number of brake assemblies will help in splitting the strain on each axle.

What types of brakes does a semi-truck have?

Ordinary small vehicles like cars use hydraulic pressure brakes in their braking system. But semi truck is different from them in this aspect. They do not use hydraulic pressure brakes in their system.

The 18-wheelers can not rely on hydraulic pressure because they require high force to stop a heavy trailer. They use air in their braking system to stop the trailer and tractor.

The hydraulic pressure system uses hydraulic fluid to build pressure, while air brakes use compressed air to build up pressure inside the system. This system is superior to the hydraulic system in many aspects.

The limited amount of brake fluid and high maintenance requirement of a hydraulic pressure brake system are limitations of this system. In comparison, air brakes use air that is found in abundance in the atmosphere.

How does the air brake system work in a semi-truck?

The air brake system in the semi-truck consists of three braking system, which includes air brakes, emergency brakes, and parking brakes.

The air brake works by compressing air with the help of a compressor. A governor will govern the pressure of the air in the compressor. Then compressed air is fed to a storage tank, and a valve is present in the tank to ensure that air flows in only one direction.

Then the air is delivered to the brake lines to move other components of the system. The air from the tank is delivered to the chambers. Then pushrod moves to push on the slack adjuster. Then cam rotates to force the rollers against the brake shoe. The shoe lining then presses against the drum to stop the wheels.

Parking brakes

It is an additional part of the air brake system. It engages when the truck is standing in the parking lot. In this system, a spring is present that keeps the break from releasing. It can prevent many dangerous situations from occurring due to the disengagement of brakes.

Emergency brakes

When air brakes fail emergency brake system operates to protect the vehicles from accidents. Some types of semi trucks have automatic emergency brakes, while others have manually operated systems.

Advantages of the air braking system

This system has many advantages for heavy vehicles like trucks and automobiles. Here is a brief description of a few of them.

More powerful

An average loaded semi-truck weighs approximately between 80000 to 85000 pounds. Such heavy loads require more power and force to stop them.

The ordinary hydraulic braking system is unable to generate force to stop it. The driver has to exert more force on the brake pedal to stop it. Exerting such power is not possible by the human body.

They are more efficient and can produce more force to stop the semi-truck quickly. They produce potential energy with compressed air, and the driver does not have to put extra force on the pedals.

Safety and reliability

It is safer than other braking systems. The hydraulic system has a limited supply of hydraulic fluid. Any leaks in the tank will weaken the power of the pedals.

The vehicle will not stop due to the decrease in fluid compression. It can be dangerous to the vehicle and driver.

Minor leaks of air from the pipes will not create any trouble. The system itself compensates for the leakage of air from the pipes. The presence of emergency brakes further protects the truck from any hazardous situation.

Less maintenance

The pressurized air brake system requires less maintenance and care as compared to the hydraulic system. You have to refill the fluid and replace the faulty parts in the hydraulic system.

You also have to flush out all the lines to maintain the system’s function. But this system is designed to work for years. It is known for its reliability and endurance. It does not wear out quickly, and you do not have to spend a lot on its maintenance.

It generally lasts for more than one million miles. In comparison, hydraulic brake systems last for more than 50000 miles. It also has a tank reservoir to store compressed air that can produce force in an emergency.

But it has a drawback: it is more costly than a hydraulic system. It is more expensive due to its complex design and tools. Replacing its tools and parts can cost you a lot.

How long do air brakes take to stop the semi-truck?

Although the pneumatic brakes work efficiently, they take longer to stop the vehicle. In comparison to the hydraulic system, there is a delay of around 2 to 3 seconds in stopping or slowing down the semi-trucks. The delay is because the air has to flow through the lines to the pedal.

The stopping distance of the air brakes is comprised of four factors

  • Perception Distance
  • Reaction distance
  • Brake lag distance
  • Effective braking distance

The air brake lag distance is different at different mph. A truck traveling at 55mph will have a brake lag distance of 30 feet. So the stopping distance of the semi-truck will be about 300 feet.

How many drums does the air brake system have?

The drums in a brake are a cylinder that is attached to the truck wheel. They are attached to the rotating shaft against which the brake shoe acts.

The drums help dissipate the heat produced during braking. A semi-truck with five axles will have ten brakes and ten drums with each one of them.

Drums are long-lasting compared to the disc brake because they have more contact area than the disc. They also produce more force as compared to the same-diameter disc.

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