Utah CDL — Air Brakes Practice Test 6

11.At 55 mph on dry pavement, roughly how much extra distance does air brake lag add?

About 5 feetAbout 100 feetAbout 32 feetAbout 450 feet

12.Why must emergency and parking brakes be held on by mechanical force?

Because springs cost less than air valvesBecause air can slowly leak off over timeBecause air brakes may not be used for parkingBecause mechanical force builds air pressure

13.Compared with a car's hydraulic brakes, how quickly do air brakes respond?

A little slower, since the air must travel through the linesExactly the same - both act instantlyFaster, because air moves quickestThey never respond unless the engine is running

14.When is it a bad idea to set the parking brakes right after coming down a steep grade?

When the air tanks are fully chargedWhenever you are on level groundWhen the brakes are still very hotWhen the engine is idling

15.The safety relief valve on the first air tank starts letting air escape. What does that tell you?

The tanks have finished draining the way they shouldThe alcohol evaporator is due for a refillThe spring brakes are on the verge of applyingSomething has gone wrong and a mechanic needs to repair it

16.On large buses, the low-pressure warning devices commonly activate at about what pressure?

80 to 85 psi20 to 30 psi55 psi125 psi

17.After you release the brakes during stab braking, how long can it take for the wheels to start rolling again?

Up to about one secondUp to ten secondsRoughly a full minuteNo time at all

18.What job does an alcohol evaporator do on a vehicle with air brakes?

It strains oil out of the compressor crankcaseIt lowers the risk of ice building up inside brake valves when it is coldIt raises the boiling point of the brake fluidIt lets you skip tank draining all winter

19.Your truck has a modulating control valve for the spring brakes. How should you use it when you park?

Tap it repeatedly until the vehicle stops rollingLeave it about halfway so the springs apply gentlyMove the lever through its full travel and lock it in that positionIgnore it and hold the foot valve down instead

20.Other air-brake vehicles such as trucks, buses, and trailers must have ABS if built on or after when?

March 1, 1997March 1, 1994July 1, 2017March 1, 1998