Moving people and goods around a country as big as ours requires a lot of power and mass. Most of us have spent time driving on the highway and are familiar with the scene of huge semis and trailers hauling lumber, food products, and merchandise to and from destinations, or the convoy of recreational vehicles on their way to the next city, lake, or campground. These vehicles are massive! They take a lot to get moving and once they are, they can cruise. But that also means they take a lot to slow down and stop.
Braking systems on large-scale commercial and recreational vehicles are vitally important to the safety of those operating them, as well as the people around them. Smaller-scale passenger vehicles use some form of hydraulic braking system. These systems use fluid to operate the brakes. On the other hand, air brakes use forced air to operate the braking system and are typically found in larger commercial vehicles. Each of these systems has pros and cons and they also have different implications for technical complexity and pricing.
What do you need to know about air brake and hydraulic brake systems? Below, we provide an overview of each system, as well as some of the advantages and disadvantages of each system.
Hydraulic Brake Systems
Hydraulic brakes use fluid to power the brakes. When the driver presses the brake pedal, the hydraulic fluid pressure increases to the point that it forces the brake pistons at each wheel to push the brake pad against the drum (or rotor with disc brakes). This causes friction, slowing the wheels, and, eventually, halting the vehicle entirely. The technology for hydraulic brakes is very similar to that used by passenger cars. The fundamental difference on larger vehicles is that the components are much larger to handle the higher weight ratings.
Hydraulic brakes can be used on vehicles with a gross vehicle weight rating (GVWR) up to a maximum of 33,000 pounds. In most cases though, hydraulic braking systems are used in vehicles up to 26,000 pounds GVWR.
Air Brake Systems
Instead of using fluid, air brakes, as the name implies, use air to generate stopping power. When the air tanks are fully pressurized, the brakes are disengaged. When the driver presses the brake pedal, air fills the brake chamber, pushing the chamber diaphragm, which turns the "S-cam," and then pushes the brake pads against the brake drum, stopping the vehicle. Then, when the brake pedal retracts, the air is released allowing the brakes to release and the wheels to roll. The compressor increases air pressure back to the system's original state.
Air brakes are recommended for vehicles with a GVWR of 26,000 pounds or more, although air brakes may be spec’d on lower-weight vehicles. This depends on how the vehicle may be used.
Air Brakes vs Hydraulic Brakes: Applications
Experts in medium-and-heavy duty vehicle manufacturing have a number of criteria they use to assess and recommend a particular braking system. In general, hydraulic brake systems are recommended in vehicles with a lighter GVWR, especially ones where the daily usage is less severe. For example, delivery vans and trucks. Hydraulic brakes work very well in stop-start traffic and where vehicle speeds are not excessive. It is important to note that hydraulic systems can be pushed beyond their performance capacity, which reduces their effectiveness.
With vehicles that have a GVWR of 26,000 pounds or less, hydraulic brakes work well. When a vehicle exceeds that rating, it usually means that loads are substantially heavier. This can overload hydraulic systems, causing the brakes to wear faster and diminish their performance. Once the GVWR exceeds 26,000 pounds, most experts recommend air brakes.
Air brakes are ideal for heavy-duty applications and should always be used in scenarios that include regular heavy towing. A key reason why air brakes are preferred in heavier trucks is their significant stopping power when they work but also, when they fail. Consider a scenario where the system has a leak in one of the brake lines. In a hydraulic system, fluid pressure diminishes to a point where there isn’t enough force to slow the wheels. Eventually, if the leak isn’t addressed, it can create a significant safety issue, reducing the vehicle’s ability to stop.
The opposite is true for air brakes. If there is a leak in the air brake lines, the air pressure decreases, which actually activates the brakes at the wheels and brings the vehicle to a stop.
Important Braking Considerations
In vehicles with a GVWR under 26,000 pounds or over 33,000 pounds, the decisions are already made. Under 26,000 pounds, hydraulic systems make the most sense and are recommended. Over 33,000 pounds, air brakes are necessary to create the right amount of stopping power for heavy payloads.
In the overlap though, between 26,000 and 33,000 pounds, one could go either way. Cost and licensing are important things to consider if equipping your vehicle with a specific braking system. Air brakes come at a premium price. An air brake system costs approximately $2,500 more than hydraulic brakes, because of the extra components to operate the system. In British Columbia, you would need to add an Air Brake Endorsement or upgrade your class of licence to operate a vehicle with air brakes, depending on the specific weights and vehicle you’re looking at.