Section 12: BRAKE AND AIR SYSTEM
PA1553
7
Change cartridge every 100,000 miles (160 000
km) or once every two years, whichever comes
first. The air dryer may be purged for mainte-
nance purposes using the remote drain valve
located in the engine compartment and
accessible through the engine compartment
R.H. side door. The valve is positioned over the
battery assembly, close to the door hinge or
close to the L.H. side of door opening depending
on type of vehicle (Fig. 2). The air filter/dryer has
a built-in governor to maintain the system
between 108 psig and 123 psig.
Maintenance and repair information is supplied
in the maintenance information annexed to this
section.
7.1 AIR FILTER/DRYER PURGE TANK
A tank is supplied to purge the air filter/dryer to
remove moisture and contaminants.
8. AIR LINES
Copper piping, nylon-reinforced tubing, and
flexible hoses are used to connect the units in
the pneumatic system, including air brake
system, suspension system and accessory
systems such as the entrance door, fresh air
damper cylinder, air horns, etc. Furthermore, the
nylon tubing is color coded to ease identification.
Refer to the following table for the complete
color identification code. Service instructions for
each type of air line are also provided under the
applicable headings.
Color Circuit
Red Secondary
Green Primary and Delivery
Yellow Parking Brake
Blue Suspension
Black Accessory
Brown Trailer Brake
8.1 COPPER PIPING
A heat dissipation copper piping assembly is
used to dissipate the heat coming from the
compressor before it enters the air filter/dryer.
Connections should be checked for leakage at
least every 6,250 miles (10 000 km) or twice a
year, whichever comes first. Tighten or replace
when necessary. When replacing copper piping,
the parts must be free of burrs, copper cuttings,
and dirt. Blow out piping with compressed air.
Any such particles will destroy sealing seats in
air control units. Also, new piping must be the
same size as the old one.
8.2 FLEXIBLE HOSES
A flexible hose is used normally where it is
impractical to use copper or nylon tubing due to
constant flexing during operation, such as brake
chamber hoses. Hose connections should be
tested for leakage at least every 6,250 miles
(10 000 km) or twice a year, whichever comes
first and tightened or replaced if necessary. Any
hose which is chafed, worn or kinked should be
replaced.
Teflon-braided stainless steel hoses used in the
engine compartment must be replaced only with
similar hoses.
8.3 NYLON TUBING
Nylon tubing is used for air lines in areas where
usage of this material is suitable. Nylon tubing is
flexible, durable, and weather resistant. When
replacing an air line, use nylon tubing only
where it has been used previously.
Nylon air lines must never be routed in areas
where temperature could exceed 200
o
F (93
o
C).
CAUTION
Nylon air lines should be used to replace
existing nylon lines only, and must comply
with the color identification code to ease
pneumatic system troubleshooting.
8.4 AIR LINE OPERATING TEST
If any trouble symptom such as slow brake
application or slow brake release indicates a
restricted or clogged air line, disconnect the
suspected tube or hose at both ends and blow
through it to clear the passage.
Inspect tubing and hose for partial restriction
that may be caused by dents or kinks. If such a
condition is found, the tubing or hose should be
replaced.
8.5 AIR LINE LEAKAGE TEST
With air system fully charged and the brakes
applied, coat all tubing and hose connections
with a soapy solution to check for air leakage.
No leakage is permitted. Leakage can
sometimes be corrected by tightening the
connection. If this fails to correct the leakage,
new fittings, nylon tubing, copper tubing,
teflon-braided stainless steel and flexible hoses
must be installed as applicable.
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