Virginia CDL — Air Brakes Practice Test 9

11.What is the role of the emergency brake portion of an air-brake system?

To hold the truck in place on a hill while it is parkedTo supply extra air to the trailer during a hard stopTo cool the brake drums after a long descentTo stop the vehicle by using parts of the service and parking brakes when a failure occurs

12.If the safety relief valve lets air escape, what does that indicate?

The system is working normally and no action is neededThe tanks simply need to be drainedSomething is wrong and the problem should be repaired by a mechanicThe alcohol evaporator is out of fluid

13.What causes brakes to fade?

Excessive heat from overusing the brakes instead of the engine to slow downToo much air pressure in the tanksCold weather freezing the liningsWater in the alcohol evaporator

14.How do you test that the parking brake will actually hold?

Rev the engine in neutral and watch the gaugeRoll downhill and count how far the vehicle travelsSet it and, in a low gear, ease the vehicle forward against it to confirm it holdsPush the brake pedal to the floor and hold it

15.On a long grade, if you must keep increasing application pressure just to hold the same speed, what is most likely happening?

The compressor is overcharging the tanksThe brakes are fading and you should slow and gear downThe governor has failed in the cut-in positionThe alcohol evaporator is working too hard

16.What defines a dual air brake system?

Two sets of controls feeding one air systemA single system with two compressorsTwo separate air systems operated by one set of controlsOne system that switches between air and hydraulic modes

17.How does the stop light switch on an air-brake vehicle operate?

A cable pulls the lights on mechanicallyThe alternator senses deceleration and powers the lampsAir pressure closes an electric switch that lights the brake lampsThe parking brake knob wires directly to the lamps

18.On a tractor or straight truck, the spring brakes typically come fully on when air pressure falls to what range?

80 to 100 psi55 to 75 psi5 to 15 psi20 to 45 psi

19.Which statement about ABS and stopping distance is accurate?

ABS always cuts your stopping distance in halfABS lengthens your stopping distance on dry roadsABS only works when you are stoppedABS does not necessarily shorten stopping distance but helps you keep control

20.When you press the pedal on an s-cam brake, what does the s-cam itself do?

It spreads the brake shoes apart against the drumIt pulls the shoes away from the drumIt clamps a rotor between two padsIt vents excess air back to the tanks