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may not operate correctly or could fail completely.
In the case of brakes, components could freeze up
or fail prematurely, Russoli noted. For a suspension,
loss of ride quality is likely as well as the
inability for the suspension to be raised or lowered,
which results in a loss of critical capabilities.
" Excessive moisture in compressed air has
caused steel air tanks to corrode internally,
which creates particulates in the air lines that
can damage the systems that use the air, " Russoli
continued. " That's especially true for transmission
control systems, and is important considering the
increased use of automated manual transmissions
that rely on compressed air to operate. "
Braking system modulators and wheel-end
pneumatic components can freeze with excessive
moisture or fail prematurely from chemical
incompatibilities with oil contaminants, Stadler
noted. " When this occurs, contaminants will
accumulate inside valves and O-rings, causing
corrosion, clogging, or internal valve damage, "
he explained. " Any internal damage or freezing
in braking components could cause sudden loss
of [anti-lock brake system] functionality or more
advanced braking or traction control functions.
" Suspension control system components can
be subjected to the same failure modes, " Stadler
continued. " Any internal damage or freezing could
cause the sudden inability to lower the suspension
to pick up or drop off a trailer. In rare cases,
if enough moisture has accumulated in the air
bags, it can affect load leveling controls and optimization
for dynamic control, resulting in loss
of productivity for load sensing adjustment and
driver comfort. "
Stadler pointed out that prolonged excessive
moisture causing internal corrosion of steel air
tanks is of particular concern because the corrosion
creates additional particulates that are subsequently
sent through to downstream systems.
" When more moisture is introduced, the rust
particulates coagulate or congeal, causing devasting
effects and often sudden, complete failure, "
Stadler said. " This type of failure has typically
targeted the air compressor governor, given
its proximity to the air tanks and small internal
mechanical components that can easily be
compromised. Any pneumatic component can be
subject to moisture or oil contamination, resulting
in a challenging diagnostic process to uncover the
issue. "
Additionally, Stadler noted that transmission
and emission systems utilizing vehicle air have
been subject to sudden failures. Transmission
control systems, like those with air-assisted clutch
actuation or overdrive assist, have been victim to
contaminated compressed air. Damage to pneumatic
components within the emissions system
are often undetectable, he added, but have caused
problems to downstream emissions components
and impacted processes.
Joe Kay, director of engineering at CumminsMeritor,
pointed out that there can be negative
consequences if water or particles get inside
suspension air bags.
" Any ingress can have
longterm affects such as non-functioning valves,
internal corrosion, etc., " he said.
LaFlamme related three areas of air system
contamination concern. One is when oil from the
» Contaminant build-up in pneumatic systems
leads to premature component wear and tear.
Haldex Air System
compressor becomes hot enough to congest the
discharge line with carbon, restricting airflow.
" The heat from this restriction expands the air
molecules, slowing system air pressure regeneration, "
he said. " Excessive oil will also corrupt the
desiccant properties in the air dryer filter.
" Another issue can be when high water content
freezes in the air system, preventing proper system
operation, " LaFlamme continued. " Excessive water
reduces the actual air volume, reducing functionality.
Impurities in water, like minerals, can cause
springs inside the valves to decay, eventually causing
the valve to malfunction and leading to failure.
Water impurities can also cause combination-style
brake actuator center seals to pass air from the
parking chamber to the service chamber. "
The third concern is alcohol. For example, when
alkyl-grouped molecules modify polymer and
elastomer components, like O-ring seals, this will
eventually cause them to malfunction.
If contaminants are somehow introduced into
the air system, Winter reported, they can increase
friction within valves. " Valves obviously have
moving parts, and contaminants can begin to
hinder their movement, so they begin to develop
operational limitations and extra resistance to
smooth component motion, " he explained. " You
can also get air leaks if the contamination gets on
seals and compromises them. Once that happens,
the seals no longer mate up properly and you can
have a leak path through any gaps.
" Contaminants can also reduce your overall
airflow in the system, and this alone can cause
problems, " Winter continued. " They can also cause
accelerated component wear within the valves.
Especially when you're dealing with a contaminant
like oil, it can begin to coat surfaces and
valves and then, if you're trying to run an O-ring
over it, that can accelerate wear. "
Depending on the type of contaminant, the
system might be exposed to a chemical attack on
the rubber components within the valve as well,
Winter pointed out. " Even a substance as seemingly
benign as water can get trapped in the wrong
place and can freeze, which will prevent a valve
from moving properly, " he said. " You could also
have water accumulation in an air line and if it
freezes, you've got a plugged system. "
Best practices: Suggestions
from suppliers
ÜEnsure the engine air filter is clean
ÜReplace the air compressor (and discharge pipe)
if it pumps excessive oil into the air system
ÜDrain reservoirs daily
ÜFollow PM instructions for air dryers
ÜAvoid inducing alcohol and lubricants into the
air system
ÜSeal gladhand connections when equipment
is decoupled
ÜConfirm that air dryers are operating properly
and change cartridges on time
ÜRegularly drain the air tanks. If oil or excessive
water is present, it may be an indication that
you need to address quickly
ÜTrain drivers to monitor the frequency of
their compressor turning on and off or when
the dryer purges; if too often, that may be an
indication of a leak
ÜNever put additives into an air system. They
can remove lubricants and collect in valves,
negatively affecting rubber seals
ÜCheck air lines for sections where water could
freeze.
Redline Detection offers a unique piece of shop
and service equipment to help technicians locate
air system leaks in a matter of minutes. The Air
Brake NanoLeak Finder is a heavy-duty diagnostic
leak detector that diagnoses high-pressure air
brake, air suspension, and air-powered systems.
The detector, used in conjunction with the included
NanoLeak Handheld Leak Locator, locates all
air brake and air-powered system leaks.
Choosing the right compressor
for service trucks
Making the right choice for mounted compressors
is important, noted manufacturer Vanair. Two of
the most popular types of air compressors are
rotary screw and reciprocating (or piston) models.
A rotary screw air compressor is oil-flooded. The
oil inside the unit acts as a lubricant, seals the rotors,
and cools the system from the heat of compression.
Key benefits to using a rotary screw compressor
include fewer moving parts and less maintenance.
A reciprocating air compressor works by using
pistons driven by a crankshaft to compress the air.
These compressors, which require an auxiliary
tank for air storage, are best suited for intermittent
use, such as on service and tire trucks.
In the end, choosing a rotary screw or reciprocating
air compressor comes down to application
and desired lifespan.
TMC Recommended Practices
address air system issues
* RP 617A - Contaminant Elimination
Procedure for Tractor, Trailer, or
Dolly Air Brake Systems
* RP 619B - Air System Inspection Procedure
* RP 630A - Air Compressor Diagnosing
for Excessive Oil Consumption
June 2023 | FleetMaintenance.com
27
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