Spicer Tire Pressure Control - Manual (Page 5)

It must also be noted that pneumatic control
system leakage can mimic the pneumatic
signature for an 11P! code, and result in false
alarms. In this case, the operator can use run
flat to proceed, however the system should be
serviced as soon as possible since leaks will
always get worse over time and eventually
cause additional service messages and make
diagnosis and repair more difficult. The use
of service diagnostic tools will greatly simpli-
fy the identification and repair of leaks.
How does the air get to the tires?
Air is routed to the tires via air seals which
have been installed in the axles. Two
approaches are used, one for non-driven
axles (steers and trailers or tag axles) and
another for drive axles. Air is routed through
the center of non-driven axles and through a
rotary joint which is mounted on the end of
the spindle. Driven axles utilize a patented air
sleeve in conjunction with a special hub.
Once the air is passed through the hub or
hub cap, it is connected through the wheel
valve to the rim with an air hose. It is impor-
tant to remember that wheels and hubs need
to be positioned properly relative to each
other to assure proper fit of the hoses to the
valve stems. Failure to do so may result in
stress on the hose or valve stem that can
result in air leakage and improper operation.
If an air line ruptures, do I lose all
of the air in the system?
The Spicer ® Tire Pressure Control System
utilizes wheel valves to assure that air is not
lost from the system in the event of air line
breakage. Air pressure only exists in the
control lines of the system when measuring,
inflating or deflating the tires. (Only the hoses
between the tires and the wheel valves are
normally pressurized). Failure of a control
line is sensed by the system and the affected
channel is shut down and the operator
notified through a service message. This
depressurized operation also guarantees that
tires will not leak down through the air seals
while the vehicle is parked, even for
extended periods.
How do the wheel valves work?
Can they malfunction?
The wheel valve is an essential part of the
Spicer System which improves overall sys-
tem safety and reliability by allowing control
lines to be depressurized unless actually
inflating, deflating or measuring tire pres-
sures. It is an extremely simple device con-
sisting of spring loaded diaphragms biased
against seats to contain air to the wheel end.
In the absence of a control signal, the springs
act against the diaphragms and seats to close
the valve. Positive pressure signals are used
to measure and inflate tires, negative pres-
sures are used to deflate.
As a result of the simple design, the wheel
valves possess an inherent high reliability,
even in the environment of a truck air system.
In fact, similar diaphragm and spring con-
cepts are used in most of the valves used in a
trucks today because of their high reliability
and ability to tolerate wide temperature
ranges and some level of contamination. The
biggest difference between the Spicer
® Tire
Pressure Control System and other systems
used on the truck is in the volume of air used.
Since inflating tires uses a large volume of
air, possibilities of contamination are greater.
Contamination is the largest single reason for
wheel valve malfunction. Measures must be
taken to prevent contamination from entering
the system.
Each wheel valve includes a filter in the port
which connects it to the tire. These filters are
intended to trap contaminants contained in
the tire and prevent them from entering the
wheel valves, and should be changed at any
time the tire is removed, either for rotation or
replacement. Service technicians must be
careful not to damage the filter by installing
adjustable fittings too deeply into the tire port.
To do so will crush the filter and possibly tear
it. Instructions in the service manual should
be followed closely.
Care must also be taken to prevent
contaminant entry any time control air lines
are disconnected. Trailer couplings are
especially critical as they may frequently be
disconnected with the trailer. For this reason,
Spicer recommends the use of an in-line air
filter in the trailer line, to prevent contamina-
tion from entering the coupling and traveling
to the trailer wheel valves. It is also important
to blow any debris from hoses, tubing and
fittings when servicing the vehicle. Instances
have been encountered wherein hose slivers
from the initial installation have been trapped
in the system, causing problems later.
What is the minimum temperature
for operation?
The Spicer ® Tire Pressure Control System
has been developed using the same industry
standards for operation to -40 degrees as
most vehicle components. Operation at tem-
peratures below that is possible, however
some service codes may be encountered
under extremely cold conditions which may
disappear when either the component warms
up under use or from increasing ambient
temperatures. These may include codes
related to temperature induced leakages, as
extremely cold temperatures will cause
materials to shrink and reduce the effective-
ness of sealing. Dana recommends that the
pneumatic control unit be placed in the cab
wherever cold weather is encountered so that
cab heat can assist in warming the unit to
enable operation.
While system operation is possible at low
temperatures, the primary reason for prob-
lems at temperatures below freezing is not
with the system components, but with the
effectiveness and maintenance of air drying
equipment. Extremely cold air has very little
moisture in it, while warm air can hold
tremendous amounts. In fact, at +80°F
(+27°C), atmospheric air can hold almost 50
times more water than at -13°F (-25°C).
Failure to monitor and maintain the air
system during warmer months will result in
entrained moisture in the air tanks and sys-
tem components that are certain to cause
problems as temperatures fall. Failure to rou-
tinely drain air tanks can result in whole water
passing from the tanks through the system,
and even into the tires where it can inhibit the
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