Do Air Brakes Have Brake Fluid?

Air brakes, or more formally known as a compressed air brake system, are commonly used in large, heavy vehicles such as trucks, buses, trailers, and trains. These brakes are usually used for these types of vehicles due to their reliability.

Do air brakes have brake fluid? Air brakes do not have brake fluid because they rely on compressed air to transmit pressure to stop a car. Air storage tanks are filled with compressed air, and when the driver steps on the brake pedal, air flows from the storage tanks to the brake chamber. This causes the brake to be engaged and the vehicle to slow down.

This is the simple explanation of air brakes not having brake fluid. If you really think about it, the “fluid” they use is just the air that the compressor stores in the tanks. Below is more about this system and the advantages and disadvantages of using this air brake system.

Why Heavy Vehicles Rely on Air Brakes

Most everyday vehicles that we see on the road and commute to work in use hydraulic brake systems. In this system, fluid is put in a reservoir and stored in what’s called a master cylinder. The fluid is pumped through hoses when you push the brake into the pistons that are mounted on the car’s wheels.

Depending on the car’s system, these pistons either push down on two brake shoes or against a brake pad. If your car has brake shoes, these cause friction against a brake drum. A brake pad uses friction against a brake rotor to slow a car down.

Hydraulic brakes are not a perfect system, which is why heavy vehicles usually rely more on air brakes. Hydraulic brakes are known to malfunction when things like a leak occur or an air bubble trapped in the brake hose or line. Maintaining these vehicles’ brakes that have to decelerate so much harder to stop because of the heavy payload would be difficult.

That’s why they turn to air brakes. Air Brake Systems are less likely to have a leak, but even in case of a leakage, the system is always funneling air back into it. If you run out of hydraulic brake fluid, there’s no process to obtain more while driving the vehicle.

Imagine a heavy moving truck having hydraulic brakes, and a leak sprung while they were close to reaching their destination. They run out of hydraulic fluid and have no way to stop. In front of them is a turn to the left a turn to the right and a park down the middle. With no possible way to stop, any decision made here probably won’t work out. Things like this have happened before and it’s the exact reason why the air brake system is so important.

The triple-valve system focuses on three main functions, which are known as charging, applying, and releasing. Charging is needed to take in the air before the brakes are even needed. Once the system has enough, the brakes will be ready to use at any moment.

When the brakes are in use, it applies air pressure, decreasing the amount in storage. During this process, the valve opens up, allowing air back into the reservoirs, while the brakes are stopping the vehicle.

Once the vehicle is stopped, and the air is done being in use, the pressure and air are released as the driver steps off the brake. This triple-valve system is still the concept for the air-brake systems that are used in today’s era of trains, buses, and trailers.

Components of Foundation Air Brake Systems

Most air brake systems are foundation systems in the modern era. It can be found in most trucks and buses that push heavy cargo. The following components and the functions of this system are listed below:

• Air Compressor and Governor: The air compressor pumps air into the tanks that store air that can be used by the brakes. The governor controls when the air compressor pumps more air into the storage tanks and when more air isn’t needed.
• Air Reservoir Tanks: These tanks hold the pressurized or compressed air. Depending on the vehicles, the number of tanks and sizes may vary.
• Drain Valves: Each air tank has a drain valve. These valves release the air tanks and drain the air in the tanks when the vehicle isn’t being driven.
• Brake Pedal: Self-explanatory pedal that sets the brake like the vehicles we know.
• Push Rod: The push rod is like a piston that connects a brake chamber to the next component, the slack adjuster.
• Slack Adjusters: This is an arm that holds the push rod to the S-cam to regulate the brake shoe’s distance from one another.
• Brake S-Cam and Shoe: The S-cam forces the brake shoes apart from each other and the brake drum. The shoe is the steel lining that forces the friction to stop the vehicle with the brake drum.
• Return Spring: This is a spring that is connected to the shoes to return it to its open position when not in use.

All of these functions come together and work simultaneously in order to operate this release system in the air brake. If you are trying to operate a vehicle with air brakes, push the emergency brake button to fill the system with air first. Once this system is pressurized, the brake will stay free.

Advantages and Disadvantages to Air Brake Systems

Air brakes have several advantages over the alternative, hydraulic brakes, which are used in lighter vehicles. Here are some of the advantages we talked about and more:

• Air supply is unlimited, so the “fluid” or air that operates the brakes can never run out. Hydraulic brakes can have leakage at any point and cause brake failure.
• The lines that are used to flow the air through the system are easier to connect than hydraulic lines. This allows the air lines to be serviced easier and easily removed and reattached.
• Because air can be stored, there is always a backup plan if the compressor fails. If this happens, the vehicle will still have a certain amount of air storage before it needs to stop and get fixed.
• Even when leaking, air brakes are more effective than a leaky hydraulic brake system. Air brake systems are created to still be able to stop the vehicle safely even while leaking. Even if there is a leak in the piping, air will still be coming in through the leak, which would enter the lines and allow the brakes to be applied.

Now, there are disadvantages to this system. If there weren’t, we would see the air brake system on every vehicle. Here are some disadvantages:

• Air brake systems are known to cost more. This cuts out the ability to use them in small vehicles that are usually competitively priced.
• Air brake systems are known to need higher maintenance and repairs. The air compression creates moisture, which can impact the operating parts around the brake system.
• Driving a vehicle with air brakes isn’t simple. Most people struggle with it from the start.
• Because most people struggle with this process, in the United States, you require a specific license to be able to drive a vehicle that uses an air brake system.  This hinders many drivers and car manufacturers from having this system.
• One more hindrance for normal drivers when it comes to air brakes is that operators must understand the brake system themselves. Drivers need to be able to understand the air pressurization system and make sure everything is working properly. Most common drivers wouldn’t put in the time to learn this.