DIGGING IN

In Gear
Where are the air tank drains?
Fairings often hide them these days.
Clear and
Present Danger
Aside from audible air leaks, you’ll never
be able to detect many air system problems
without proper test procedures
By Jim Park
Tractor and trailer air systems may
be among the least proactively maintained
parts of trucks. Put another
way, fleets tend to ignore them until
there’s a problem.
There are two serious flaws with this
thinking. First, a problem other than an
air leak will probably not be noticed until
it’s too late. And second, the new annual
inspection requirements that debuted in
2014 mandate checking certain systems
that never had to be checked in the past.
If you aren’t following these new inspection
requirements, you’re missing a vital
part of the air system inspection – and a
valuable early warning.
With that said, air systems are generally
pretty reliable and not prone to
failures. That can be a blessing and curse.
It’s good that they are reliable, but that
reliability can lead to a false sense of
security. There are plenty of documented
cases of air system failures, other than
leaks or ruptures, causing calamity.
What can go wrong with a bunch of
tubing and few valves? The most obvious
is a leak, and leaks are relatively easy to
detect and repair. But there are standards
to which systems must be maintained,
and pressure loss rate is one of them.
Depending on the vehicle configuration,
the system pressure loss rate cannot
exceed 3 to 6 psi over 60 seconds at full
system pressure with the brakes fully
applied. You may not be able to hear a
slight leak like that, especially in a noisy
shop, but the reservoir pressure gauge
will reveal the leak.
“There’s now a requirement to
perform an air system leakage test on
trailers at every annual inspection, as
well as to inspect the air tanks, and you
have to test the air loss rate,” notes Rolf
VanderZwaag, manager of maintenance
and technical issues at the Ontario
Trucking Association. “Those are specific
tests required as part of an annual
inspection. These are tests that fleets may
not have been doing in the past because
they never felt they needed to.” Now it’s
captured in National Safety Code (NSC)
Standard 11 – Maintenance and Periodic
Inspection Standards, October 2014.
“These inspections must be done. If not,
it’s a violation,” he says.
In addition to leaks, crimped air lines
are not uncommon. Unless the crimp
closes off the line completely, it could be
difficult to detect. Crimps or blockages
can slow the delivery of air to the brake
actuators, resulting in low application
pressure at one or more wheel ends,
depending on where the blockage exists.
Air lines tucked into harnesses can
also suffer chafing and external rubbing
that may compromise the integrity of the
line, or result in an Out of Service condition
if sufficiently worn when it’s found
by a roadside inspector.
These items are all now part of the
new annual vehicle inspection procedures
found in NSC 11. Section 3A, parts
1-12, include much of the new air system
inspection requirements.
Near-invisible deficiencies
In normal service, some problems will
not be readily evident. But a proper
inspection can reveal them – if you know
what to look for. Take, for example, the
one-way and two-way check valves and
pressure protection valves use to isolate
the primary and secondary air systems on
tractors since 1975.
“These valves can fail, usually from
age and contamination,” says Rick Mello,
senior technical services representative at
Haldex Brake Products. “If either system
experiences a single failure, the [working
system] becomes the truck’s emergency
brakes. They must be operationally
checked on a regular basis or you risk
losing both brake systems during a single
failure. This means you would have no
emergency brakes.”
Historically, one-way check valves were
used between the first air tank [the wet
tank] and the two service tanks [primary
and secondary tanks]. Some trucks today
don’t have wet tanks and use pressure
46 TODAY’S TRUCKING