june2021 - 14

system leak could be originating from other places
in the system such as the brake chamber. "
Hawkins said some of today's heavy duty trucks
have characteristics that make them more susceptible
to a leak. Historically, main lines were heavy
duty copper with threaded connections. Leaks rarely
emerged unless rub-through occurred.
" Then things went to rubber to the brakes on
the axles, " Hawkins said. " Fleets never really had
a problem because everything had a good heavy
duty connection and everything was still threaded
between parts. "
Today, things have started to change. For speed
of manufacturing, some OEs have gone to plastic
with quick-coupler fittings. There are also large
bundles of air lines because air is being supplied
to not only the brakes, but also to the suspension
and the cab, among other areas of the vehicle.
" Things just aren't as robust as they used to be, "
Hawkins related.
Richard Nagel, director of marketing and
customer solutions for air supply and drivetrain
at Bendix Commercial Vehicle Systems, said that
whether a push-to-connect fitting is made of brass
or nylon, it doesn't always create the perfect seal.
That can lead to small air leaks depending on the
quality of the cut in the line.
" These fittings can also be highly susceptible to
chemicals and temperature fluctuations, " Nagel
pointed out.
Bendix is a developer of active safety technologies,
air brake charging, and control systems for
medium and heavy duty vehicles and trailers.
Corrosion is a major
cause of leaks
Roadway surface treatments have also become
a major cause for air brake system leaks. To help
mitigate this issue, fleets should have strong
inspection processes in place, as well as quality
components that are designed to be up to the task.
" Some of the new de-icing treatments that
are being used more regularly, like magnesium
chloride, are causing a lot of corrosion issues, "
Nagel said.
» Examples of air dryer corrosion and
air dryer purge valve corrosion.
Photos courtesy of Bendix Commercial Vehicle Systems
Technicians not only need a thorough winterprep
regimen for trucks and trailers, but also a
post-winter regimen to look for any damage that
may have emerged over the winter months.
The transition from winter to spring and
into summer creates other potential corrosion-related
issues for fleets. Nagel said
the contrast of cold temperatures and heat
coming off of the engine can spell trouble
in the following ways:
» Air dryer corrosion can cause major
issues for air systems. Bendix has
" reinforced " its AD-HF air dryer by
incorporating a two-piece, highstrength
aluminum casting with an
integrated purge volume reservoir,
which eliminates the need for a steel
tank that is more susceptible to
corrosion. Additionally, the primary
housing is treated with an additional
layer of corrosion protection.
Photo courtesy of Bendix Commercial Vehicle Systems
" Our sniffing device is mapped
exclusively to the signature air
produced inside the machine. "
Mark Hawkins, head of technical products, Redline Detection
ÜTrapped moisture due to freeze/thaw
ÜHumidity and moisture
ÜMetals expanding and contracting
ÜPlastics softening and hardening
Air lines, valves, and fittings aside, fleets must
also pay close attention to their air system's
air dryer. Once again, corrosion can become a
major issue - especially with respect to the seats
around the purge and pressure protection valves,
as well as the governor connection. Additionally,
traditional steel air tanks can corrode and develop
small punctures. Regular inspections should
include a diligent search for signs of corrosion
and cracking, along with breaks in any plastic
air-line tubing that connects the air dryer to the
air system.
Nagel says some air system component manufacturers
have been working to address the
corrosion issue. For instance, Bendix introduced
its AD-HF Air Dryer in late 2019. It features a
two-piece, high-strength aluminum casting with
an integrated purge volume reservoir, which
eliminates the need for a steel tank. Additionally,
the primary housing is treated with an additional
layer of corrosion protection.
Tips on finding and
repairing leaks
According to Nagel, there are several warning
signs that an air brake system may be experiencing
a leak. For instance, the system may be
charging more often than usual. The system may
also be taking considerably longer to charge,
such as three or four minutes as opposed to just
one or two.
If it is suspected that an air leak may be
occurring, technicians have their work cut out
for them. Locating the leak (or leaks) is the first
hurdle to overcome. Then the leak needs to be
properly repaired.
Before any tractor-trailer can leave the lot, it
should have an air brake leak-down test to ensure
that it meets DOT standards.
" Testing will ensure that the brake system has
not leaked down more than 5 psi in 60 seconds, "
said Jeffrey Lerman, vice president of sales and
marketing at Proflex+ Distribution, a developer of
automotive diagnostic solutions including a lineup
of smoke leak detectors. " If the tractor-trailer fails
testing, you know you have a leak. "
Most of the time, Lerman explained, a
failed leak test suggests that there is a ripped
diaphragm in one of the service brake chambers,
or that one of the valves is leaking. It could also
be as simple as one of the hoses being cracked
14 Fleet Maintenance | June 2021
june2021

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