BRAKE SYSTEM PRINCIPLES OF OPERATION
Gladhands The gladhands are the coupling point for the air supply between the trailer and the towing vehicle.
They are marked, one for emergency and the other for service, to ensure correct hookup.
Air Lines The air lines extend from the gladhands to supply service and emergency air to the relay
valve, air reservoir, and brake air chamber.
Relay Valve Controls the braking system of the trailer. Based on the air pressure signals received
from the towing vehicle, it will apply or release the service brakes or it will initiate an emergency brake
Air Reservoir The air reservoir stores the system air pressure, 95 psi (655 kPa) minimum, that
operates the brake system. Pressure to the reservoir is initially supplied, and then maintained through
the emergency supply line from the towing vehicle through the relay valve.
Brake Chamber The brake chamber controls the movement of the s-cam on the brake system causing the
activation and release of the brakes as the air flow from the air reservior is passed into and out of the chamber.
Brake shoes The two brake shoes on each wheel assembly are spread apart by the mechanical
movement of the S-CAM. The brake shoes cause friction to slow or stop the trailer.