Gladhands - The gladhands are the coupling point for the trailer to towing vehicle. They are marked, one for
emergency and the other for service, to ensure correct hookup.
Air Filters - The air filters clean air from towing vehicle of moisture and foreign matter,
Air Lines - The air lines extend from the air filters 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 application.
Air Reservoir - The air reservoir stores the system air pressure (60 psi (413.7 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 Air Chamber - The brake air chamber converts air pressure to mechanical motion. This movement, through
the hydraulic master cylinder, applies the brakes. When air pressure in the brake air chamber is released, spring
action releases the brakes.
Hydraulic Master Cylinder - The hydraulic master cylinder converts the mechanical motion of the brake air
chamber to hydraulic pressure.
Wheel Cylinders - The wheel cylinders convert system hydraulic pressure to mechanical motion and force the
brake lining against the brakedrum.
Brakeshoes - The two brakeshoes on each wheel assembly are spread apart by the mechanical movement of
the wheel cylinders. The brakeshoes cause friction to slow or stop the trailer.