control pedal, either the front or rear service brakes will not be operating, causing a longer
stopping distance. Bring the vehicle to a safe stop, and have the air system repaired before
On tractor trailer vehicles if both the primary and secondary systems become inoperative, the
trailer service brakes or spring parking brakes will automatically apply when air pressure drops to
35-45 psi (242-310 kPa The tractor spring parking brakes will automatically apply when air
pressure drops below 45 psi (310 Kpa
Fuel is drawn from the supply tank through the primary fuel filter by a gear-type fuel pump.
From there, the fuel is forced through the secondary fuel filter and into the fuel inlet manifold in
the cylinder head and to the injectors. Excess
supply tank through the outlet connecting line.
injectors, it serves to cool the injectors and to
fuel is returned, through a restricted fitting, to the
Since the fuel is constantly circulating through the
carry off any air in the fuel system.