Air Lines; Flexible Hoses; Nylon Tubing; Air Line Operating Test - PREVOST H3-41 Maintenance Manual

SECTION 12: BRAKE AND AIR SYSTEM

10. AIR LINES

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, 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
Primary system,
Green
Supply/Delivery
Secondary system
Red
Parking & emergency brake
Brown
system, trailer Brake
Suspension
Blue
Accessories, valve exhaust
Black &
tube
translucent
Air compressor unload
Yellow
10.1

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 or belt tensioner air cylinder
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.
10.2

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
14 PA1621 Maintenance Manual All Series | Revised June 2020
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.
10.3
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.
condition is found, the tubing or hose should be
replaced.
10.4
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
sometimes be corrected by tightening the
connection. If this fails to correct the leakage,
new
Teflon-braided stainless steel and flexible hoses
must be installed as applicable.
10.5
Inspect all lines for cuts, swelling, kinks or other
damage or deterioration. Check for lines being
pinched by other components. Retaining clips
and ties must be in place.
Any support or bracket should be in good
condition and mounted firmly in position. Hose
spring guards should be in usable condition and
not distorted. Particular attention should be given
to long lines. Any supporting component (clips,
ties, grommets, etc.) must be secured to prevent
against unnecessary vibration and eventual
loosening of connection.
should be repaired. Be sure nylon lines are not
near areas of intense heat. Check for any
F (93 C). missing grommets or loose material where
o o
chafing or cutting may occur. Replace with new
material as required. In general, lines should be
CAUTION

AIR LINE OPERATING TEST

AIR LINE LEAKAGE TEST

leakage is permitted.
fittings, nylon tubing,

MAINTENANCE

If such a
Leakage can
copper tubing,
Any detected leak