Virginia CDL — Air Brakes Practice Test 2

11.How does the controlled braking method work in an emergency stop?

Lock the wheels on purpose to stop fasterUse only the trailer hand valveBrake as firmly as you can short of locking the wheels, keeping steering inputs smallAlternate between the parking brake and the pedal

12.Compared with hydraulic brakes, why do air brakes add extra stopping distance called brake lag?

The compressor must first refill the tanksAir takes about a half second or more to reach the brakesThe parking brakes must release firstThe driver must shift gears before braking

13.Some buses have dual parking control valves with a separate air tank. What is that separate tank for?

To release the spring brakes a few times so the vehicle can be moved in an emergencyTo supply unlimited air for continued drivingTo run the alcohol evaporator in winterTo power the ABS computer if the battery dies

14.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

15.Around what pressure does the governor 'cut in' and let the compressor start pumping again?

About 125 psiAbout 20 psiAbout 150 psiAbout 100 psi

16.What is a 'wig wag' low-pressure warning device?

A gauge needle that flashes redA mechanical arm that drops into the driver's view when pressure gets lowA buzzer that sounds only above cut-out pressureA valve that automatically drains the tanks

17.On large buses, the low-pressure warning devices commonly signal at what pressure?

20 to 30 psi40 to 45 psi120 to 125 psi80 to 85 psi

18.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

19.What is the purpose of a modulating control valve for the spring brakes?

It automatically drains the air tanks when parkedIt limits pressure to the front brakes on iceIt lets the driver apply the spring brakes gradually if the service brakes failIt recharges the secondary system from the primary

20.When checking manual slack adjusters on s-cam brakes, roughly how much movement suggests the brakes need adjustment?

Any movement at allMore than three inches of movementMore than about one inch of movementMovement only when the engine is off