Figure 3-46.Hand brake valve.
Figure 3-48.-Air-over-hydraulic power cylinder.
NOTE: More information about the air brake
system is in the chapter covering tractor and trailer
AIR-OVER-HYDRAULIC BRAKE SYSTEM
An air-over-hydraulic brake system is shown in
figure 3-47. This system combines the use of
compressed air and hydraulic pressure for brake
operation. The air-over-hydraulic brake system has an
trailer brakes without applying the truck or tractor
air-over-hydraulic power cylinder (fig. 3-48) that
brakes. The hand brake valve or independent trailer
contains an air cylinder and a hydraulic cylinder in
control valve, as shown in figures 3-44 and 3-46,
tandem. Each cylinder is fitted with a piston and a
provides the operator control of the trailing load at all
common rod. The air piston is of greater diameter than
the hydraulic piston. This difference in the two pistons
Figure 3-47.-Typical air-over-hydraulic brake system.