Air Brake Manual

30
14
31
16
39
14
Application air directed from either the foot or hand
valve causes control pressure to move through the
control (service) line and act on the relay emergency
valve (39). This control pressure will cause the relay
emergency valve to direct air from the trailer reservoir
(16) to the trailer brake chambers (14). The pressure
directed by the relay emergency valve to the trailer
brake chambers will be the same as the pressure
directed to the tractor brake chambers. In such a
system, brake lag time has been minimized with the
addition of the trailer reservoir and relay emergency
valve.
Release of the foot or hand valve stops the flow of
application air. The relay portion of the valve returns to
its original position, stopping the flow of air pressure.
The exhausting ports of the valve exhaust the air
pressure from the brake chambers, releasing the
brakes. In this system, the brakes of both the tractor
and trailer can be released quickly.
Caution: Trailer brakes must not be used to hold a parked
vehicle that is left unattended. Loss of pressure will
result in loss of brakes. Always set the parking brake.
Emergency Application
22 21
14
16
39
14
48