New Hampshire CDL — Air Brakes Practice Test 2

1.In the manual's description of the air compressor governor, what is the "cut-in" pressure?

The tank pressure, around 100 psi, at which the governor lets the compressor pump againThe tank pressure, around 125 psi, at which the governor stops the compressorThe pressure at which the safety relief valve opens to protect the tanksThe pressure at which the low air warning signal has to come on

2.Wedge brakes and S-cam brakes use different mechanisms. What does the manual's description show they have in common?

Both force brake shoes against the inside of a brake drumBoth use a power screw to clamp a rotorBoth rely on a caliper with lining padsBoth are self-adjusting on every vehicle

3.Step 3 of the seven-step inspection in Section 2 has you look at the gauges once the engine is running. What does it say about the air pressure gauge?

It should hold steady at 55 psi while the engine idlesIt should climb from 50 psi to 90 psi in no more than 3 minutes, and you go on building to governor cut-outIt should reach 150 psi before you release the parking brakeIt should drop 3 psi each minute until the engine warms up

4.A drum brake stops the vehicle by pressing its shoes and linings outward on the drum. Besides slowing the vehicle, what does the manual say the resulting friction creates?

HeatExtra air pressure in the tanksMoisture in the brake chambersSlack in the push rods

5.Which of these Step 7 checks does the manual have you run with the engine shut off?

The governor cut-out checkThe rate of air pressure buildup checkThe service brake testThe low pressure warning signal test

6.The safety relief valve is usually set to open at a fixed pressure. Using the manual's usual numbers, about how far above the governor's cut-out level is that?

About 5 psiAbout 25 psiAbout 50 psiAbout 95 psi

7.Which of these air brake parts does the driver work from inside the cab?

The safety relief valveThe S-camThe parking brake controlThe slack adjuster

8.Section 5 covers brakes that are too hot or too wet to set the parking brakes on. Which pairing of condition and remedy matches the manual?

Very hot brakes: set the parking brakes to hold the heat in. Wet brakes: drain the air tanksVery hot brakes: let them cool first. Wet brakes: drive in a low gear with light brake pressure until they heat up and dryVery hot brakes: pump the pedal rapidly. Wet brakes: set the parking brakes at onceVery hot brakes: work the parking knob in and out. Wet brakes: top up the alcohol evaporator

9.The low air warning light and buzzer on a dual-system truck go quiet while pressure is still building. Is that the manual's signal that the truck is ready to drive?

Yes. The warning shutting off means both systems are fully chargedNo. The warning shuts off at a manufacturer's value above 55 psi, but you should wait for at least 100 psi in both systemsYes, as long as the primary gauge reads higher than the secondaryNo. You must wait for the safety relief valve to open first

10.For which units does the manual say it may be hard to tell whether ABS is fitted?

Truck tractors built after March 1, 1997Buses with dual parking control valvesAny vehicle whose malfunction lamp is yellowTowed units built before the Department of Transportation required ABS