1-10. AIRBRAKE SYSTEM (Con't)
Emergency Relay Valve. The emergency relay valve
is located above and beween the front and rear axles.
up the brake application by releasing reservoir air to airbrake chambers for service brakes. It also automatically
applies emergency braking if the semitrailer breaks away from the tractor. Available connections are to the emergency
air line, service air line, air reservoir tanks, airbrake chambers, and to an exhaust port that vents the used compressed
Airbrake Chamber Assembly. There are four airbrake chambers, two on each axle. The airbrake chamber converts the
energy of compressed air into the mechanical force and motion necessary to operate the brake. As air pressure enters
the airbrake chamber behind the diaphragm of the chamber, the diaphragm pushes the push rod ouward. The outward
motion of the push rod rotates the slack adjuster.
Brakeshoe Assembly. There are two brakeshoes on each wheel and tire assembly. The rotating slack adjuster turns the
camshaft and the brake S-cam. The brake S-cam pushes the brakeshoes ouward to contact the inside of the drum.
This action applies the brakes. When all air pressure is released from the airbrake chamber, the brakeshoe return
spring and airbrake chamber spring return the brakeshoes to a released position.
1-11. LIGHTING SYSTEM
The intervehicular receptacle on the front of the semitrailer gooseneck receives lighting power from the tractor. The
power is sent through a single wiring harness to the clearance lights and composite lights.
Composite Tail, Turn, Stop, and Blackout Lights. The composite tail, turn, stop, and blackout lights, located on left and
right rear of semitrailer, have four bulbs each. One bulb functions as a taillight when the service lights are turned to ON,
and one bulb functions as both turn and stopllght. The third and fourth bulbs function as blackout light and blackout
stoplight when the blackout light switch is turned to ON. The blackout lights automatically turn off the tail, stop, turn,
and clearance lights if both switches are on at the same time.