Figure 7-53.Relay emergency valve.
installed, by closing the emergency line cutout valve
and uncoupling the emergency brake line, the valve
can be checked. Either way the trailer brakes should
apply automatically. Trailer brakes should release, in
the first case, when the tractor protection valve control
lever is moved to the NORMAL position, and, in the
second case, when the emergency line is coupled and
the cutout valve is opened.
The relay emergency valve is checked for leakage
by application of soapsuds with the brakes released.
Check the emergency air line coupling with soapsuds
to determine leakage with the valve in emergency
application position. Leakage may be caused by dirt or
worn parts which may be corrected by cleaning and/or
replacing the unit.
Check valves are located in the lines of air brake
systems to prevent the loss of air should the line
rupture while in operation. These are placed at the
entrance of the main air tanks and prevent the loss of air
should the inlet line from the compressor fail. The
ball-type check valve (fig. 7-54) is typical of the type
used on trailer braking systems. Check valves may be
either disc or ball and double or single units.
Regardless of their design, their function is the same.
Figure 7-54.Ball-type single check valve.