You’re hauling a capacity load of wide flange beams and have come to a 6-mile 7% downhill grade. That means steep and curves. It’s ok. You’re trained for this. After all, air brakes never go out, right? Well, that’s what you’re counting on at this moment. You’ve cleared weight at the weigh station, taken a deep breath, downshifted at the top since you can’t downshift on the way down, turned on your emergency flashers, and you take the plunge.
What happens when air brakes fail? When the air brake system is not pressurized enough, a low-air pressure alarm will sound. In these cases, semi-trucks and trailers, airplanes, buses, trains, and large trucks (such as fire engines) are equipped with a back-up emergency braking system for use when air brakes fail. Steep grades, like the one discussed above, also usually have emergency truck escape ramps built for these types of situations.
Keep reading for more information on how air brakes work and situations that may cause air brake failure.
Can Air Brakes Fail?
Although there have been significant improvements in air brake technology, they can still fail.
These days, however, air brake failure is usually (not always) due to human error and/or poor maintenance practices. Before digging into what can cause air brake failure, it’s important to understand the different components of an air brake system.
A Refresher for Understanding Your Air Brake System
Since you had to pass the air brake certification for your CDL designation, you had all of this information memorized at one point. In case you are lucky enough to work for a reputable company that has a certified mechanic responsible for the truck’s maintenance, here’s a refresher.
This Yahoo Images diagram of the air brake system is very detailed and will provide you with a reference point for this article.
When studying for your CDL, you were tested on the following:
- How to properly engage and disengage the truck’s parking brake
It’s a good idea to occasionally test your parking brake by making sure the brake is set, letting the air pressure build up, shifting into gear, and attempting to drive. Your vehicle shouldn’t move.
- How to test your air system
After you allow the system to charge and fill, drive your truck a short distance, and apply about 90-pounds of pressure for approximately one minute. You shouldn’t experience more than 3 pounds per square inch (psi) of leakage during this exercise. More than that needs attention.
Remember… the harder you press the brake, the more air pressure that is applied to the system. If at all possible, refrain from ever slamming on your brakes.
Now that you’ve checked for leakage, pump your brakes. When the chamber has decreased to about 60 psi, an alarm should sound. Keep pumping your brakes to test that the protection valve pops out between 40 and 20 psi.
Now that those systems are working, stop shift into neutral, apply your parking brake, and check to see how long it takes the air pressure to build back up. The governor should blow out between about 125 and 130 psi.
If any of these tests fail, your air brake system needs attention.
- The Air Brake Compressor Cooling Process
You know that the compressor is controlled by the governor, but when was the last time the compressor’s cooling process was checked? You need to know whether your compressor has its own cooling system and if it has oil levels that need to be checked or if it is tied to the vehicle’s cooling system.
- Are Your Air Brake Reservoirs Holding Enough Compressed Air?
You should be able to stop several times before the reservoir gets empty completely. When you’re stopped, be sure to trip the drain valve to empty any oil or water that has collected in the reservoirs. If water freezes in your reservoir, it can damage the reservoir, the valves, or the lines that control your system.
What Can Cause Air Brakes to Fail?
The ability to stop your vehicle is something you – and everyone around you – counts on. Brake failure would be something from a driver’s nightmare.
Although there are several fail-safes built into current systems, there are a few things that can still cause air brakes to fail.
- Pumping the brakes
Yes, you were just told to pump the brakes to test them, but the expectation is that you conducted your test in a controlled environment – not in traffic.
If you continuously pump the brakes while you are driving, the compressor will not be able to refill the reservoirs to an operational level. Once the pressure has dropped below the point where they can adequately function, your brakes will not work.
- Brake Fade
If you continually depress or ride your brake pedal, not only will you drain your air reservoirs, you will also overheat your brake drums.
When the drum is overheated, it separates and expands away from the brake shoes. Too much heat on the brake drum can cause either it or the tire it is controlling to catch on fire.
What to do in the Event of an Emergency
If you experience the worst-case scenario and lose your brakes, there are a couple of things you should do to get stopped.
- Use your emergency brake to get stopped
Pull as far to the right as you can and activate your emergency brake.
This is going to cause a significant amount of tension on your vehicle. Make sure you have a firm grip on the steering wheel with both hands.
- Get on a downhill grade
Use an escape ramp if possible. They’re usually placed before curves during a long, steep grade.
This will be a crazy, somewhat scary, bumpy ride, but it will get you stopped.
False Reasons Drivers Don’t Want to Use Escape Ramps When Air Brakes Fail
Fines
There also tends to be a perception that if a driver uses an escape ramp, he or she will be fined by the Department of Transportation.
There is inconsistent information about this topic, but for the most part, the consensus is that there are not fines directly associated with using the ramp. It also seems to vary by state.
- In general, fees are typically assessed for towing the vehicle out of the escape ramp and for repairing it for use.
- There will also be expenses associated with repairing any vehicle undercarriage damage.
- Fines, on the other hand, may be handed down if it is determined that the vehicle’s air brake system was faulty and not properly maintained. Those fines can be significant as additional driving charges, such as reckless endangerment and/or faulty equipment, may then be assessed.
Adding these numbers up may seem daunting, and tempt you not to use a ramp if you find yourself in need of one, but think of it this way – would you prefer to use an escape ramp and go home to your family or be responsible not only for your own death but probably for others’ too.
Stigma
There’s a false stigma about using escape ramps. Some think that it reflects badly on the driver as if you didn’t know what you were doing.
In some cases, that’s an accurate assessment – someone was too green for the situation and didn’t handle it properly. In the case of an experienced driver, though, most likely, there were extenuating circumstances outside of his or her control.
Ease on Down the Road
This article has discussed a few worst-case scenarios but remember…current air brake systems have several fail-safes and warning systems. Paying attention to these protocols will give you the confidence you need to deliver your cargo safely.