june2021 - 16

Delivering high-quality air
Ensuring the air coming from the
compressor is clean and dry can improve
the operation of connected vehicle
systems and help prevent leaks.
Richard Nagel, director of marketing and customer
solutions - air supply & drivetrain, Bendix
Where the pneumatic brake systems
on yesterday's trucks relied
primarily on valves with mechanical
seats and springs, commercial
vehicles today come equipped
with increased automation and
more sophisticated computer-controlled
solenoid valves that can
cycle more frequently and have
tighter tolerances. It is imperative
for fleets to make sure vehicle
compressors are delivering air that
will keep connected components
operating safely and ensure the
overall health of the air system.
" Oil-coalescing air dryer filters have
been used on trucks for almost
10 years, and most air dryers now
come standard with them, " Nagel
observed. " What differentiates
an oil-coalescing cartridge from
a regular dryer cartridge is an
additional filter that removes oil
aerosols that are passed along
by the compressor. These are
collected into larger drops, and
then gravity-fed into the bottom
of the cartridge where they're
expelled during the purge cycle. "
" Defining 'high-quality' air is difficult
because there isn't an industry
standard, " said Richard Nagel,
director of marketing and customer
solutions for air supply and
drivetrain at Bendix Commercial
Vehicle Systems. " And yet, because
systems today are more sophisticated
than they used to be, they
also require a higher quality of air. "
Dryness contributes to air quality,
Nagel noted, and is probably the
first thing that comes to mind
when a fleet thinks about air. While
the air dryer removes water from
the air system, compressed air
also contains other contaminants,
including oil aerosols and in some
extreme cases, oil vapors. The air
dryer wasn't traditionally equipped
to remove these types of contaminants,
and if they pass into the air
system, they can cause problems
in connected systems like brake
valves, emissions controls, and
automated manual transmissions.
High-quality air isn't just dry: It's
clean. No system can prevent all
contaminants, particularly oil, but
the goal, Nagel said, is to minimize
what gets into the service tanks.
And that's where a high-performance
air compressor and oil-coalescing
technology are important.
While the design of these cartridges
differs by manufacturer
(the oil-coalescing filter can be
placed so the air passes through
it before the desiccant or after),
all of them offer some level of oil
protection, especially when new.
Over time, design variances will
provide different efficiencies, and
they can't remove oil vapors - but
oil-coalescing filters can be very
effective at removing most of the
oil particulates that a compressor
passes into the air system.
ยป Example of air dryer corrosion.
Photo courtesy of Bendix Commercial Vehicle Systems
the air supply. And again, when
we look at the differences in compressors,
we see a lot of variables
that affect that air quality. The
compressor itself is the source of
most contaminants that go into
an air system, and if it passes a
lot of oil, over time it can overwhelm
the capabilities of even the
best-designed oil-coalescing filter. "
The first thing most people
ask when considering what
air compressor to spec is how
much air it will deliver. Every
vehicle's demand for air depends
on a range of factors, including
how the truck is used, its
number of axles, and whether
it's equipped with additional
air-powered technologies like
bulk offloading systems. Nagel
pointed out, however, that quality
matters as much as quantity.
" If you're not getting good air
from your compressor, it's hard to
make that air better once it gets
into the service tanks, " he said. " A
compressor is basically an engine
with a reciprocating piston that
uses oil from the engine crankcase
and passes some of that oil into
16 Fleet Maintenance | June 2021
Many variables contribute to a
compressor's performance over
the life of a vehicle. Some of these
are attributable to engineering
and design; like how it's cooled,
the geometry of its bore, operational
tolerances, and single
versus dual pistons, along with
the design of the piston rings on
each compressor piston. Other
variables are determined by how
the compressor is used - if the
compressor is turbocharged, that
can help keep oil from passing
through the compressor. Most
compressors today are normally
aspirated and the location of the
air inlet, along with other characteristics
of the inlet can also
affect the amount oil that passes.
Duty cycle and air demand are
also major factors. The former
is a measure of the average time
that a compressor is producing
high pressure over the amount
of time it is rotating, both at
pressure and unloaded.
" Most compressors run at about
a 15-20 percent duty cycle - so
if a truck runs 2,000 hours a
year, at a 15 percent duty cycle,
the compressor is producing
charged air pressure for about
300 hours, and then is unloaded
for 1,700, " Nagel explained. " But
if you have a lot of air demand, or
your system has multiple leaks,
then your compressor will run
longer and hotter, and will most
likely pass more oil over time. "
It can be tough for fleets to determine
the quality of air that comes
out of the compressor: It's natural
to focus on more noticeable things
like leaks or moisture in the service
tanks, so the first sign of excessive
oil passing is usually a valve failure.
" That's when they'll start doing
some investigation, and they'll
notice a lot of oil in the system, "
Nagel said. " The first thing they
tend to do after that is replace
the air dryer cartridge, and if it's
not an oil-coalescing cartridge,
they'll upgrade to one of those.
And depending on how much
oil that compressor passes, that
solution may work for a while. "
Bendix recommends taking a close
look when examining the service
tanks for moisture, checking to
see whether there is oil mixed in
with any water that comes out.
A second tip is to inspect the
compressor's discharge line. If
it's especially dirty or fouled with
carbon buildup or evidence of oil,
it's a sign that the problem is at the
source from the compressor itself.
Whether the next step is replacing
the compressor entirely or
opting to replace an oil-coalescing
cartridge more often than
usual depends on things like the
vehicle's age and the fleet's maintenance
planning. It's also worth
noting that when installing a new
compressor, a remanufactured
compressor, or a rebuilt compressor
the fleet may still experience
some oil passing depending on
the specifications and long-term
performance of that compressor.


Table of Contents for the Digital Edition of june2021

Uptime: The path to predictive maintenance
Editor's Note: Using resources wisely
Equipment: Getting to the bottom of air brake system leaks
In the Bay: Commercial vehicle clutch care
Shop Operations: How digitizing driver communication can improve maintenance
Fluid & Filtration: Why fleets shouldn't skimp on oil filters
Technology Trends: Gaining an advantage
Management: KPI fundamentals
Economic Outlook: Economic recovery update
Fleet Parts & Components
Tools & Equipment
Guest editorial: Benefits of remote brake system monitoring
june2021 - 1
june2021 - 2
june2021 - 3
june2021 - 4
june2021 - 5
june2021 - 6
june2021 - 7
june2021 - Uptime: The path to predictive maintenance
june2021 - 9
june2021 - Editor's Note: Using resources wisely
june2021 - 11
june2021 - Equipment: Getting to the bottom of air brake system leaks
june2021 - 13
june2021 - 14
june2021 - 15
june2021 - 16
june2021 - 17
june2021 - In the Bay: Commercial vehicle clutch care
june2021 - 19
june2021 - 20
june2021 - 21
june2021 - 22
june2021 - 23
june2021 - Shop Operations: How digitizing driver communication can improve maintenance
june2021 - 25
june2021 - 26
june2021 - 27
june2021 - 28
june2021 - 29
june2021 - 30
june2021 - 31
june2021 - 32
june2021 - 33
june2021 - Fluid & Filtration: Why fleets shouldn't skimp on oil filters
june2021 - 35
june2021 - 36
june2021 - 37
june2021 - Technology Trends: Gaining an advantage
june2021 - 39
june2021 - Management: KPI fundamentals
june2021 - Economic Outlook: Economic recovery update
june2021 - Fleet Parts & Components
june2021 - 43
june2021 - Tools & Equipment
june2021 - 45
june2021 - 46
june2021 - 47
june2021 - 48
june2021 - Classifieds
june2021 - Guest editorial: Benefits of remote brake system monitoring
june2021 - 51
june2021 - 52