Note: If the truck has oversized air tanks, it could take longer than 45 seconds for the pressure to rise from 85 psi to 100 psi (consult the manufacturer’s specifications). With the engine running, pump the brake pedal repeatedly until the governor starts the compressor and the pressure in the primary tank starts increasing. Observe when the pressure stops increasing in the primary tank. Pressure should rise from 85 psi to 100 psi within 45 seconds at normal RPMs. Note the pressure on the primary air gauge. (Straight trucks do not have a trailer protection valve.) This should be between 20 psi and 45 psi.ĭouble-check that the transmission is in neutral. Resume pumping the brake pedal until the parking brake valve and trailer protection valve pop out. The low pressure warning light will extinguish at the same time. Switch the ignition key to “off” so that the buzzer will stop sounding. The light and buzzer should activate before the tank pressure is below 60 psi (on dual systems: the tank with the lowest pressure). Pump the brake pedal repeatedly, until the low pressure warning light illuminates and the buzzer sounds. Switch the ignition key to “on” (so that the dashboard lights are illuminated). With air tanks charged with enough air that the low pressure warning light is not on:
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Volvo bus driving instructions driver#
Any time a driver is assigned to a new or unfamiliar piece of equipment, an Air Brake Check should be performed. An Air Brake Check is a group of individual tests that collectively determine if a truck’s air brakes are safe to operate.Īn Air Brake Check is also a handy way to diagnose problems a driver might be having with the brakes on a truck. To pass your CDL driving test, you will be required to perform an Air Brake Check.
Volvo bus driving instructions full#
A Wig-Wag is a brightly colored paddle that swings down, in full view of the driver, when triggered by the warning system. Some older equipment might have a Wig-Wag instead of a warning light and buzzer. Warning: Never operate the truck with less than 100 psi in all air tanks.
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Also, it might be impossible to release the truck’s brakes until the air pressure builds up. Warning lights will be illuminated and buzzers will sound. When a truck is first started, it is normal for the air pressure to be low.
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Older straight trucks might have only one tank and one gauge (primary only). Trucks will usually have two pressure tanks and two pressure gauges (primary and secondary). Governor (controls the air compressor and maintains air pressure in the primary tank between 100 psi and 125 psi) Pressure gauge(s) that monitor air pressure in various tanks Other pieces of equipment that are not part of the warning system (but used during tests and inspections) are: The parking brake should not pop out first. Older systems were designed to pop out the parking brake valve first, then the trailer protection valve-but this has become uncommon. The parking brake valve and trailer protection valve pop out between 20 psi and 45 psi. The low pressure warning light illuminates above 60 psi. (More accurately, the parking brake valve and trailer protection valve will pop out causing the spring brakes to lock-up.) If the pressure of the brake system continues to drop, the warning system will lock up the brakes. If the pressure of the brake system drops, a warning light is illuminated and a buzzer sounds. The Low Pressure Warning System is designed to warn a driver of a dangerous low air pressure condition.