South Carolina CDL — Air Brakes Practice Test 9

1.When should you avoid setting the parking brakes?

Any time the vehicle is fully loadedWhenever the engine is still runningOn any downhill gradeWhen the brakes are very hot, or very wet in freezing temperatures

2.When testing the service brakes, at what speed and how should you apply them?

Creep forward at roughly five mph, then press the pedal firmlyDrive at highway speed and slam the brakesStay parked and press the pedal lightlyCoast in neutral at 20 mph and tap the brakes

3.What is the purpose of the stop light switch in an air brake system?

To warn the driver of low tank pressureTo measure application pressure at the pedalTo shut off the compressor at cut-outTo turn on the brake lights when the brakes are applied

4.The moment the low-pressure warning light and buzzer first activate, what is the safest action to take?

Keep driving until the spring brakes apply on their ownPump the pedal to rebuild pressureStop safely as soon as it activates, while you still control the brakesRelease the parking brake and coast

5.Some vehicles such as buses have dual parking control valves fed by a separate air tank. What is a key limitation of that separate tank?

It only works when the engine is runningIt cannot release the spring brakes at allIt holds only enough air to release the spring brakes a few timesIt must be drained before every use

6.What does an alcohol evaporator do in some air brake systems?

It lowers the chance of ice forming in the brake valves during cold weatherIt boosts the compressor's pumping speedIt replaces the need to drain the tanksIt cushions the brake pedal for a softer feel

7.Why is it important to drain the air tanks regularly?

To relieve pressure so the safety valve does not openTo let the governor recalibrate its cut-out pointTo keep the parking brakes from locking overnightTo remove water and oil that could cause brake failure

8.A visible low air pressure warning must come on before tank pressure falls below what level on most vehicles?

80 psi60 psi100 psi45 psi

9.What is the purpose of a modulating control valve on the dash of some vehicles?

To drain the air tanks automaticallyTo apply the spring brakes gradually if the service brakes failTo boost front-brake pressure on iceTo measure how much air is left in the tanks

10.Total stopping distance for an air brake vehicle is made up of four parts. Which set lists them correctly?

Perception, reaction, tank, and braking distancePerception, reaction, brake lag, and braking distanceReaction, brake lag, cut-in, and braking distancePerception, brake fade, reaction, and braking distance