Bendix Commercial Vehicle Systems TU-FLO 700 COMPRESSOR 10/04 - Manual (Page 2)

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OPERATION
The compressor is driven by the vehicle engine and is
operating continuously while the engine is running. Actual
compression of air is controlled by the compressor unloading
mechanism and the governor. The governor is generally
mounted on the compressor and maintains the brake system
air pressure to a preset maximum and minimum pressure
level.
INTAKE AND COMPRESSION OF AIR (LOADED)
During the down stroke of the piston, a slight vacuum is
created between the ton of the piston and the head, causing
the flat circular inlet valve to move up and off its seat. (Note
the flat square discharge valve remains on its seat.)
Atmospheric air is drawn through the air strainer by the open
inlet valve and into the cylinder (see Fig. 2). As the piston
begins its upward stroke, the air that was drawn into the
cylinder on the down stroke is being compressed. Air
pressure on top of the inlet valve plus the force of its spring,
returns the inlet valve to its seat. The piston continues the
upward stroke and compressed air then flows by the open
discharge valve, into the discharge line and on to the
reservoirs (see Fig. 3). As the piston reaches the top of its
stroke and starts down, the discharge valve spring and air
pressure in the discharge line returns the discharge valve to
its seat. This prevents the compressed air in the discharge
line from returning to the cylinder bore as the intake and
compression cycle is repeated.
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 into the cavity beneath the unloader pistons. This
lifts the unloader pistons and plungers. The plungers move
up and hold the inlet valves off their seats (see Figure 4).
With the inlet valves held off their seats by the unloader
pistons and plungers, air is pumped back and forth between
the two cylinders. When air is used from the reservoir and
the pressure drops to the cut-in setting of the governor, the
governor closes and exhausts the air from beneath the
unloader pistons. The unloader saddle spring forces the
saddle, pistons and plungers down 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
specifically, 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
MACK
MACK
"FOXHEAD"
CUMMINS
DETROIT
DIESEL
VARIOUS COMPRESSOR MOUNTINGS