Understanding The Use Of Air Brakes In Semi Trucks

Semi Trucks
April 12, 2020

How much do you know about cars, SUVs, semi trucks, etc.? What about the brake systems on them? You may be thinking, “Brakes are brakes, right?” Not exactly. Particularly with semi-trucks, something called air brakes are used. If you’ve done any driving at all, you’ve likely heard them. Unmistakable for their “hisssss”, they’ve likely generated from the semi next to you at the stoplight as it rolls to a stop. But why are the brakes in a semi-truck so different than others? Why are air brakes used? Cars and SUVs use hydraulic brakes, so why can’t those be used on semis?

Let’s find out!

Why Do Semi Trucks Use Air Brakes?

A lot has to do with resources and their availability and reliability. Air brakes are more likely to be used, the heavier the vehicle. Manual refilling of small car brake lines with hydraulic fluid happens solely at service centers. (Unless you know how to do it yourself.) On the other hand, the air used in air brakes for semis is everywhere! Of course, that’s only the tip of the iceberg, but it is significant.

How Air Brakes Function

Now that you’ve been introduced to air brakes, let’s see how they function. To a regulated pressure, storage tanks are filled by a compressor. A governor sets the pressure. So that air only flows through the line one way, a valve is in place. Air tanks won’t leak even if the compressor leaks. Through the brake lines, air is fed to move a series of brake components, cams, and rods, in varying pressures (resulting from brake pedal pressure).

In the previously referred to hydraulic brake systems in SUVs and cars, the entire system can fail if there is a leak in the brake line. That’s because, to slow the vehicle by brake activation, pressure is needed and cannot be replenished in the case of a leak. Clearly, hydraulics would be far too dangerous if used on heavy-duty equipment such as a fully loaded truck.

An Emergency System for Semi Trucks

The air brake system on semis has an emergency feature. It automatically kicks in should a pressure of below 45 psi suddenly exist. In tractor-type vehicles such as semis, this emergency system is mandatory. In the case of emergency breaking, all of the drive wheels are held in place by strong springs and pistons until 65 psi air pressure returns, allowing the driving position to once again result. There is a simple switch on the dash that will also engage these emergency brakes. In the case of multiple trailers, all brakes on all trailers can be activated by the driver. Should trailers separate from each other, automatically, emergency brakes engage.

Air Brake Maintenance

Without going into great detail, the maintenance on air brake systems is so much simpler than the maintenance routine and procedures required on hydraulic systems, it’s astounding. It has everything to do with pressure, air bubbles, flushing out the system, etc. Air brakes save labor and time (as far as maintenance is concerned) because technicians just have to replace a faulty or leaking line, and they’re good to go. That’s oversimplified, but true, nonetheless.

Trust Your Brake Maintenance to Mickey Genuine Parts

How are the air brakes on your fleet? When is the last time you had them serviced or inspected? As important as brakes are to something as large as a semi-truck, there is no room for failure. You can trust your fleet to the competent technicians employed at every one of our certified service centers. These centers are conveniently located throughout the United States. If you have any questions or would like to schedule maintenance, contact Mickey Genuine Parts today.

Same day shipping

On all stock parts orders received by 2 PM EST

CONTACT US

For fast & convenient customer support

Dedicated Team

Excellent Services Since 1904