The Air Brake Charging System
compressed air for the braking system as well as other air
accessories for the vehicle. The system usually consists
Optional "Ping" Tank
of an air compressor, governor, discharge line, air dryer,
and service reservoir.
Oil Coalescing Filter
(Governor plus Synchro valve
for the Bendix
FIGURE 6A - SYSTEM DRAWING
brake charging system performance which may require
installed in the cylinder head (Tu-Flo
550/750) or close to
additional maintenance. Factors that add to the duty cycle
the compressor discharge port and protects against over
are: air suspension, additional air accessories, use of an
pressurizing the compressor in the event of a discharge
undersized compressor, frequent stops, excessive leakage
from ﬁ ttings, connections, lines, chambers or valves, etc.
DISCHARGE LINE TEMPERATURE
Refer to Table A in the Troubleshooting section for a guide
to various duty cycles and the consideration that must be
When the temperature of the compressed air that enters
given to maintenance of other components.
the air dryer is within the normal range, the air dryer can
remove most of the charging system oil. If the temperature
of the compressed air is above the normal range, oil as
While the original compressor installation is usually
oil-vapor is able to pass through the air dryer and into the
completed by the vehicle manufacturer, conditions of
air system. Larger diameter discharge lines and/or longer
operation and maintenance may require additional
discharge line lengths can help reduce the temperature.
consideration. The following presents base guidelines.
The air dryer contains a ﬁ lter that collects oil droplets, and
a desiccant bed that removes almost all of the remaining
water vapor. The compressed air is then passed to the air
The discharge line allows the air, water-vapor and oil-vapor
brake service (supply) reservoir. The oil droplets and the
mixture to cool between the compressor and air dryer or
water collected are automatically purged when the governor
reservoir. The typical size of a vehicle's discharge line,
reaches its "cut-out" setting.
(see column 2 of Table A in the Troubleshooting section)
assumes a compressor with a normal (less than 25%) duty
cycle, operating in a temperate climate. See Bendix and/or
other air dryer manufacturer guidelines as needed.
The discharge line must maintain a constant slope down
from the compressor to the air dryer inlet ﬁ tting or reservoir
to avoid low points where ice may form and block the ﬂ ow.
If, instead, ice blockages occur at the air dryer or reservoir
inlet, insulation may be added here, or if the inlet ﬁ tting is
a typical 90 degree ﬁ tting, it may be changed to a straight
or 45 degree ﬁ tting. Shorter discharge line lengths or
insulation may be required in cold climates.
While not all compressors and charging systems are
equipped with a discharge line safety valve this component
FIGURE 6B - DISCHARGE LINE SAFETY VALVE
is recommended. The discharge line safety valve is