Wisconsin CDL — Air Brakes Practice Test 5

11.What does an alcohol evaporator do for an air brake system?

It filters oil out of the compressed airIt raises the boiling point of the brake fluidIt reduces the risk of ice forming in the brake valves in cold weatherIt removes the need to drain the tanks each day

12.At about what tank pressure does the governor let the compressor begin pumping again?

Around 150 psiAround 100 psi, the cut-in levelAround 45 psiAround 20 psi

13.If your tanks have manually operated drain valves, how often should you drain them?

Only when the low-pressure warning comes onAt the end of every day you driveAbout once a monthOnly before a long downhill grade

14.Only the tractor of your combination has ABS, and the trailer starts to swing out while you are braking hard. What should you do?

Ease up on the pedal when it is safe to, until the trailer falls back into linePush the pedal down harder so the trailer brakes drag it backApply the trailer hand valve fully and steer toward the shoulderPull the parking brake knob out to straighten the rig

15.Why is it important to empty the air storage tanks?

To lower the pressure so the brakes release fasterTo let fresh air replace stale air in the linesTo keep the alcohol evaporator from overfillingWater and oil collect inside, and the water can freeze and cause brake failure

16.What is 'brake lag' in an air brake system?

The half-second or more it takes air to reach and work the brakesThe delay before the compressor cuts inThe time a driver needs to notice a hazardThe gap between setting and releasing the parking brake

17.During a normal stop with a manual transmission, when should you push in the clutch?

As soon as you touch the brake pedalAbout halfway through the stopNot until the engine rpm has dropped close to idleOnly after the vehicle has fully stopped

18.An automatic front wheel limiting valve sends full air to the front brakes under what condition?

When the brakes are applied hard, at about 60 psi or moreOnly when the driver moves the cab control to 'slippery'Whenever the parking brake is releasedOnly at speeds below 20 mph

19.In a dual system, what happens if one of the two systems loses most of its pressure?

Either the front or rear brakes will not work fully, so stopping takes longerThe other system automatically doubles its outputThe spring brakes lock every wheel at onceNothing changes because the two systems are identical

20.What does a supply pressure gauge tell the driver?

How much pressure is going to the brakes at that instantHow much air pressure is being held in the tanksWhether the parking brakes are setThe temperature of the brake drums