AIR HOSES AND FITTINGS
Air hoses and fittings (fig. 7-55) provide a means
of making a flexible air connection between points on a
vehicle which change their position in relation to each
other or between two vehicles. All air brake assemblies
used to connect the air brake systems from one vehicle
to another are equipped with detachable fittings and
When installing a hose assembly where both ends
are permanently connected, use the air hose connector
assembly at each end as the union to permit tightening
the hose connectors in place. Loosen the nut on one of
the connector assemblies and then turn the hose in the
loose connector to avoid kinking the hose.
To prevent dirt and moisture from entering unused
air lines, use dummy couplings (fig. 7-56). The two
types of dummy couplings are as follows:
Bracket-type couplings are mounted to the
vehicle for storage of unused hose.
Chain-type couplings are attached to the vehicle
by a chain and placed in couplings mounted on
SYSTEM SWITCHES AND INDICATORS
The switches and indicators in an air brake system
are designed as safety devices. The two most common
safety devices found in an air brake system are the
low-pressure warning indicator and the stoplight
Low-Pressure Warning Indicator
The low-pressure warning indicator (fig. 7-57) is
an electro-pneumatic switch connected with a warning
buzzer and, in some designs, a warning light or both. It
remains in the OPEN position when air pressure is
above approximately 60 psi. When pressure drops
below 60 psi, the spring forces the diaphragm down
and closes the contacts, which operate the warning
Figure 7-56.Dummy couplings.
Figure 7-57.Low-pressure warning indicator.
device. Normal operating pressure is 60 psi, plus or
minus 6 pounds.
Stoplight switches (fig. 7-58) in an air brake
system are electro-pneumatic devices, which operate
in conjunction with the treadle valve to close the
Figure 7-55.Air hose and fittings.