TM 9-2330-373-14 & P
1-7 LOCATION AND DESCRIPTION OF MAJOR COMPONENTS (cont)
(2) RELAY VALVE
Located at center of dolly, just forward of front axle.
It directly controls service-brakes by controlling flow of air
to and from air reservoir.
Is connected to emergency and service air lines, air
reservoir, and brake air chambers.
Automatically applies brakes if semi trailer breaks away
from towing vehicle. Brakes also apply automatically if
there is a serious leak in the emergency air line.
(3) HYDRAULIC MASTER CYLINDER AND
BRAKE AIR CHAMBER
A hydraulic master cylinder (1) is attached to each brake
air chamber (2).
One assembly is mounted at center of dolly, towards the
front and one is mounted at the rear of the dolly, forward
of air reservoir.
Master cylinder converts movement of brake air chamber
push rod into hydraulic pressure to apply brakes.
1. Hydraulic master cylinder
2. Brake air chamber
(4) HYDRAULIC WHEEL CYLINDER
Two are mounted on each brake backing plate.
It actuates brake shoes outward to force brake linings
against brake drums.
Each wheel cylinder is connected to hydraulic master
cylinder with tubing.
A bleeder valve on each wheel cylinder is used to bleed
air from the system.
TA 314696
1-13
