Volvo VNL 780 Operator's Manual page 322

312 OPERATION
Foot Brake Valve
The foot brake valve is directly connected to the brake pedal. The valve gives a progressive
output against the pedal travel. This allows better control of the pressure in the first half of
the pedal travel. In the last half of the pedal travel, the pressure output increase is faster.
The foot brake valve applies the service brakes, incorporating both the primary and secondary
air systems. The primary system controls the rear brakes and the secondary system controls
the front brakes. The foot brake valve receives air from the compressed air tanks. Air
pressure is then delivered to the wheel brake chambers as required by the amount of pressure
exerted on the foot brake pedal. The brake chamber force then applies the wheel brakes.
From the operator's viewpoint, operating the foot brake valve of a vehicle equipped with air
brakes differs very little from the operation of a conventionally braked vehicle. Because
the operation of the brake pedal requires scarcely more effort than depressing the average
throttle pedal, air brakes are naturally much easier to control. If the driver gives full attention
to the following suggestions, a little experience will make him/her thoroughly familiar with
the air-controlled braking of this vehicle.
DANGER
Failure to observe these precautions
can result in loss of vehicle control and
serious personal injury or death.