Volvo VNL 780 Operator's Manual page 321

OPERATION 311
W3005171
Master Warning Tell-Tale
An important feature of the brake system is that an automatic spring brake application does
not take place as a result of an air loss in only one of the two circuits. In this case, brake
control remains in the foot brake valve. In each air pressure gauge, there is a warning light
connected to a low pressure switch that comes on if air pressure goes below 420 kPa (60
psi). At the same time, the buzzer will sound and the main warning tell-tale will come on.
This pressure drop warns the operator to make a manual emergency stop before an automatic
emergency stop takes place.
Brake System Controls
The air compressor, governor, pressure regulator valve and reservoirs are control devices.
Their function is to build up, maintain and control air pressure in the reservoirs. This is so
that pressure is held constant between the minimum and maximum range established for
air brake operation.
The brake valve, quick release valve, brake chambers and slack adjusters are application
devices. They distribute the air pressure and convert its energy into the mechanical force
necessary to apply or release the brakes.