Bendix Commercial Vehicle Systems TU-FLO 750 COMPRESSOR 6/08 - Manual (Page 3)

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governor closes and exhausts the air from above
the unloader pistons. The unloader springs force the
pistons upward and the inlet valves return to their seats.
Compression is then resumed.
COMPRESSOR & THE AIR BRAKE SYSTEM
GENERAL
The compressor is part of the total air brake system, more
specifi cally, the charging portion of the air brake system.
As a component in the overall system its condition, duty
cycle, proper installation and operation will directly affect
other components in the system.
Powered by the vehicle engine, the air compressor
builds the air pressure for the air brake system. The air
compressor is typically cooled by the engine coolant
system, lubricated by the engine oil supply and has its inlet
connected to the engine induction system.
As the atmospheric air is compressed, all the water vapor
originally in the air is carried along into the air system, as
well as a small amount of the lubricating oil as vapor. If an
air dryer is not used to remove these contaminants prior
to entering the air system, the majority, but not all, will
condense in the reservoirs. The quantity of contaminants
that reach the air system depends on several factors
including installation, maintenance and contaminant
handling devices in the system. These contaminants must
either be eliminated prior to entering the air system or after
they enter.
GOVERNOR
PORT
AIR
INLET
PORT
INLET
VALVE
OPEN
PISTON
MOVING
DOWN
DISCHARGE
VALVE
CLOSED
GOVERNOR
PORT
INLET
VALVE
CLOSED
PISTON
MOVING
UP
FIGURE 4 - OPERATIONAL-LOADED (INTAKE)
FIGURE 5 - OPERATIONAL-LOADED (COMPRESSION)
GOVERNOR
PORT
DISCHARGE
PORT
AIR
INLET
PORT
FIGURE 6 - OPERATIONAL-UNLOADED
DISCHARGE
VALVE
CLOSED
UNLOADER
PISTON
DISCHARGE
VALVE
OPEN
AIR
INLET
PORT
line from returning to the cylinder bore as the intake and
compression cycle is reseated.
NON-COMPRESSION OF AIR (UNLOADED)
When air pressure in the reservoir reaches the cut-out
setting of the governor, the governor allows air to pass from
the reservoir, through the governor and into the cavity above
the unloader pistons. The unloader pistons move down
holding the inlet valves off their seats (see Figure 6.) With
the inlet valves held off their seats by the unloader pistons,
air is pumped back and forth between the two cylinders, and
the discharge valves remain closed. When air pressure from
the reservoir drops to the cut-in setting of the governor, the
INLET VALVE
HELD OPEN
BY UNLOADER
PISTON
AIR
DISCHARGE
PORT
AIR
DISCHARGE
PORT