As a regular sight on our nation’s roads and highways, semi trucks are a vital part of the stream of commerce. In fact, without them and the billions of pounds of cargo that they transport, the economy would come to a grinding halt.
As a regular sight on our nation’s roads and highways, semi trucks are a vital part of the stream of commerce. In fact, without them and the billions of pounds of cargo that they transport, the economy would come to a grinding halt. But because of their large size and incredible weight when fully loaded, semi trucks require special technologies to make them safe to drive and this includes air brakes.
Semi-trucks rely on air brakes to come to a stop because hydraulic brakes, like those found on passenger cars, have inadequate stopping power. In addition, air brakes are more reliable, provide greater protection against brake failure, and have vital safety features like built-in emergency braking.
In many ways, semi trucks are the engine that makes the economy of this country go. But their power and hauling capacity are such that special precautions must be taken to protect life and property along the roadways upon which they travel and chief among them are air brakes. So why do semi-trucks use air brakes? The science-based answers are below so read on.
Why Do Semi Trucks Use Air Brakes? (And Why Does It Matter?)
When considering the reasons why semi trucks use air brakes, it is important to first understand why the type of brakes used by semi trucks even matters at all. The first thing to consider is what type of motor vehicle we are talking about here and just how many of them are out there on the roads today. Here are a few noteworthy statistics that help provide the right perspective:
- Over 72% of all the freight in the entire country has been moved at some point in its journey on commercial trucks
- This equates to over 10 billion pounds of cargo in 2020 alone
- Hundreds of billions of miles each year are logged by trucks on the nation’s roads and highways
- There are over 37 million trucks used for commercial purposes and this includes nearly 4 million class 8 trucks (a category that includes semi trucks)
To say that semi trucks are vital to the nation’s economic health would be an understatement and these figures just go to show the incredible number of them traversing roadways across the country. Not only that, but an individual semi-truck can measure up to 70 feet in length (the tractor and the trailer) and weigh nearly 80,000 pounds total when fully loaded.
This is a huge amount of mass traveling at highway speeds or navigating crowded city streets. And this is why what type of brakes semi trucks use matters a great deal.
The Science Behind Air Brakes and Why Semi Trucks Need Them
When it comes to braking systems on motor vehicles, there are two basic types: hydraulic and air (pneumatic). Hydraulic brake systems rely on pressurized brake fluid in brake lines to provide the necessary action that engages the brakes. This is the type of system found on passenger vehicles. In contrast, large commercial vehicles like semi trucks, have air brakes to stop their motion when needed.
Air Brakes Work Differently Than Hydraulic Brakes
There are several key differences between hydraulic and air brakes and recognizing what these are help to explain why semi trucks use the latter rather than the former:
- Where hydraulic brake lines only pressurize when the brake pedal is pressed down, air brake lines are constantly under pressure
- Any leak of brake fluid in a hydraulic system will result in a loss of braking power but in an air brake system, the air compressor can make up for a minor loss of air pressure and in a scenario involving a major air leak, the built-in failsafe measure will engage the emergency brakes
- A hydraulic brake system has a fixed amount of the braking substrate (e.g., the brake fluid) and any loss cannot be replenished without servicing the vehicle; in contrast, an air brake system is designed to recharge the air pressure as needed
- Running hydraulic brake lines from the tractor to the entire length of the entire trailer (up to 70 feet total) is not feasible, whereas air brake lines can easily and safely run that distance
- Air brake lines can be quickly connected and disconnected using the quick-connect feature built into modern air brake hose fittings, meaning that the air brake lines from tractors can be disconnected from one trailer and connected to another in a matter of minutes
Given the obvious differences between semi trucks and passenger cars, it is easy to understand why they would utilize different types of braking systems. In order to gain an even deeper understanding of why semi trucks use air brakes, it is necessary to examine the major components of this type of braking system, starting with where all that air comes from.
Air Brakes Stop Semi Trucks Safely and Effectively
The concept of air brakes to stop large, heavy vehicles has actually been around for over a hundred years. In the late 1800s, George Westinghouse invented air brakes for use on trains and rail cars so the eventual application of this braking technology (as opposed to the hydraulic brakes found on passenger cars) to heavy commercial vehicles like semi trucks was a natural transition.
To truly understand the advantages and benefits of using air brakes on semi-trucks, it is necessary to examine the major components of this type o