Air Brake Systems
challenging world of expressways, mountain roads, heavier loads,
and greater horsepower, places a heavy burden on today's brake
systems. Truck air brake systems have gotten much more complicated
during the past 20 years to keep up with these increased braking
demands. Trucks traveling faster, can stop quicker today.
Many innovations contribute to this braking improvement, and the
purpose of this topic is to explain all of those brake components
which make up today's air brake systems. Once you understand the
brake components and what they do, then you can easily fault isolate
As you can see from the list below, today's air brakes cover a
lot of information. There are no prerequisites for this topic,
so lets get started and figure out how this entire braking science
all works together.
of your rig is delayed for two reasons. The first delay factor
is the amount of time it takes your brain to realize that you
need to make a panic stop, and the additional time it takes for
your body to move your foot to the brake pedal and start pushing
on the brake. It is reasonable to consider 1-1/2 seconds to get
your foot on the brake for an unexpected panic stop. At 60-MPH,
you travel 135-feet, nearly 2-1/2 times the length of your rig,
before you can even get your foot on the brake pedal. Refer to
the Oklahoma City High School experiment at http://oas.okstate.edu/ojas/hopper.htm
for their conclusions about brake application reaction times.
Although their test was to determine what effect music volume
level had upon brake delays, they proved convincingly that the
average person requires 1.55-seconds to apply the brakes for an
unexpected situation. If the above website link fails, we will
mirror a portion of their web page experiment data which can be
second delay factor is the time that it actually takes your brake
system to start generating the stopping friction. This includes
the time it takes the air pressure from your brake pedal to start
charging the brake chambers, and the amount of time it takes for
your slack adjusters to take the slack out of the brake chamber
linkage, and to start generating brake friction. This whole process
can easily exceed 1/2 second, so now your rig has traveled 2 seconds
or 180 feet at 60-MPH (nearly 4 rig lengths) before the first
braking action actually takes place.
happens if a car or truck suddenly pulls out 150 feet in front
of you while you are going 60-MPH? You will probably hit that
car or truck before your brakes ever get a chance to engage. Just
some food for thought. The whole purpose of this section is to
get you to realize just how big of a factor speed plays when dealing
with an unexpected and sudden braking situation.
We hope you have benefited from this topic and will see speed
in a different way than you used to.
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