STEMCO CentriFuse® Brake Drum Manufacturing, Chattanooga, TN.
Designed for performance. Made with pride.
Built by STEMCO.
Some companies buy components from other companies
and just put their own label on them. That’s not us. We value
the importance of roadway safety too much to rely on the
workmanship of anyone but our employees. From our brake
drums manufactured in Chattanooga, TN to our wheel seals,
made in Longview, TX to the air springs coming out of San Luis
Potosi, Mexico to the friction and brake shoes assembled into
wheel kits, made in Rome, GA and our king pins from
Millington, MI, we make the products we sell, and we
make them with pride.
Making the Roadways Safer® | STEMCO.com | 800-527-8492
November/December 2017 | VehicleServicePros.com 35
and the selective catalytic reduction system (SCR),
which reduces nitrogen oxide (NOx).
Th e DPF system consists of the following:
• Diesel Oxidation Catalyst (DOC) – Th e DOC
reduces particulate matter and oxidizes carbon
monoxide and hydrocarbons.
• DPF – Th is fi lter is designed to remove more
than 90 percent of particulates out of the exhaust,
according to Raymond Parrish, Service Engineer
at Cummins.
Cummins designs, distributes and services
diesel and natural gas engines and related technologies,
including fuel system, controls, air
handling, fi ltration, emission solutions and electrical
power generation systems.
Th e SCR system consists of these components:
• Diesel Exhaust Fluid (DEF) – A solution made
of urea and deionized water. DEF is introduced
into the exhaust stream to reduce NOx emissions.
• DEF pump – A part of the DEF delivery system
that vacuums DEF from the tank, through the
pump, fi lters the DEF and primes and maintains
pressure between the DEF pump and doser.
• DEF doser – Th e doser injects DEF into the
exhaust system.
• Decomposition chamber – Th is assists in mixing
the exhaust stream with DEF prior to the SCR.
• SCR – Th is is the catalyst for the chemical
reaction that transforms the combination of the
exhaust stream and decomposed DEF to meet
regulations for NOx emissions.
“Th e DOC and DPF work together at the front
end of the system to reduce carbon monoxide
and hydrocarbons, but more importantly, capture
soot and ash in the exhaust system to reduce the
risk of those particles reaching the atmosphere,”
Parrish explains.
“From there, the exhaust moves through a
mixing chamber that introduces DEF … needed for
the chemical reaction to reduce NOx in the SCR.
Th e resulting ‘exhaust’ that gets reintroduced into
the atmosphere is comprised of harmless nitrogen
gas and water vapor.”
In addition to the primary components of the
aft ertreatment system, there are also sensors. A
diff erential pressure sensor estimates captured
particles in the DPF. Exhaust
gas temperature sensors monitor
the system temperatures.
NOx sensors measure the NOx
conversion. PM (particulate
matter) sensors, also known as
soot sensors, measure particulates
in the exhaust (mainly ash
and soot). All of these sensors
indicate when the aft ertreatment
system needs repair or
maintenance.
Aftertreatment
system maintenance
Th e DPF collects diesel particulates
in the diesel engine’s
exhaust. Over time, this fi lter
can become clogged. To ensure
that the DPF continues to work
eff ectively, it should be serviced
regularly. DPF service intervals
are specifi ed by engine manufacturers,
so be sure to consult
your service manual to determine
how oft en the DPFs in
your fl eet should be cleaned
or replaced.
“Cummins recommends
replacement with a reconditioned
DPF instead of air
cleaning,” says Parrish. “A
reconditioned DPF ensures
performance results and eff ective
service events. Th e DPF
should be serviced when dash
lamps notify the operators,
or when your service manual
specifi es.”
Scott Barraclough, technology
product manager for Mack
Trucks, adds, “Mack recommends
cleaning the DPF every
400,000 miles or 10,000 hours.
Many Mack dealers can now
clean DPFs in-house. Th ey can
also exchange your soiled DPF
for a cleaned one.”
Mack Trucks is a manufacturer
of heavy duty Class 8 trucks,
engines and transmissions.
It is important that drivers
pay attention to aft ertreatment
system warning indicators and
symbols. Th ese lamps notify
the driver to take action to
ensure the health of the aft ertreatment
system. If ignored,
it can result in damage to
the system and derate conditions,
including torque and speed reductions,
Cummins’ Parrish says.
“Ignoring maintenance can result in reduced
performance and possible permanent damage
to emission control components,” Barraclough
says. A damaged DPF can cause expensive
repairs that could be avoided with regular system
maintenance.
Continued Page 37
» Medium and heavy duty diesel-powered
trucks have adopted complex exhaust or
emission aftertreatment systems.
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