Various Compressor Mountings; Intake And Compression Of Air (Loaded); Non-Compression Of Air (Unloaded) - BENDIX TU-FLO 501 AIR COMPRESSOR Manual

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FIGURE 1 - VARIOUS COMPRESSOR MOUNTINGS
All Tu-Flo ® 501 compressors utilize the engine's pressurized
oil system to lubricate the internal moving parts.
A nameplate is attached to the crankcase to identify the
compressor. The nameplate displays a Bendix piece number
or in some cases an engine or vehicle manufacturer's piece
number, along with a serial number.
FIGURE 2 - COMPRESSOR NAMEPLATE
OPERATION
General
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 top 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
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open inlet valve and into the cylinder (see Fig. 4). 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. 5). 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 Fig. 6).
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.
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