Page 192 - Driving Commercial Vehicles Manual+

chapter 8 — air brakes

Check the air dryer operation by periodically looking for water in the
driving tip reservoirs. More than a few drops may indicate that the air dryer or
compressor needs servicing.
If you notice more than a
few drops of water when you
drain the supply reservoir,
the air dryer or compressor
may need servicing.

There’s also an integrated air dryer system that’s common with most modern
truck manufacturers. This system combines the spin-on filter, dryer and
governor into one unit. It also includes a purge reservoir that provides the
air volume to purge all moisture and contaminants from the dryer cartridge,
each time the air compressor unloads. The former ‘wet’ or ‘supply’ reservoir
isn’t needed in this system. There are pressure protection valves to protect
the primary and secondary service reservoirs and any air accessories from
a pressure loss. These valves are factory set and shouldn’t be adjusted. A
unique feature is that air pressure builds in one service reservoir first. When
pressure reaches approximately 100 psi the other reservoir will begin to fill.
Pressure in both service reservoirs and the air accessories circuit will then build
to full pressure. Maximum pressure may be up to 135 psi.

Alcohol evaporators and alcohol injectors

Alcohol evaporators and alcohol injectors are optional devices that
fast fact introduce a small amount of alcohol vapour into the air system. The alcohol
vapour combines with any moisture that may be present. In effect, the alcohol
Even if the air brake acts as an anti-freeze, lowering the freezing point of any moisture that’s
system includes an alcohol collected in the air system.
evaporator or alcohol
injector, air reservoirs must Alcohol evaporators are connected to the inlet side of the compressor so that
still be drained regularly. alcohol vapour is drawn in and compressed along with the intake air, which is
then carried throughout the system.
Alcohol injectors are installed in the compressor discharge line between
the compressor and the supply reservoir. The discharge air passes through
a venturi (a tube with a narrow section, which causes air flowing through
the tube to create a vacuum), picking up alcohol vapour and carrying it
throughout the system.

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