Pennsylvania CDL — Air Brakes: Safe Driving Practices Practice Test

Question 1

A safety relief valve is usually set to release air at what pressure?

Accepted Answer

150 psi — The safety relief valve normally opens at 150 psi to protect the system from too much pressure.

Answer

100 psi

Answer

55 psi

Answer

120 psi

Question 2

On a vehicle with an application pressure gauge, needing more and more pressure to hold the same speed is a sign of what?

Accepted Answer

The brakes are fading, so you should slow down and downshift — When you must keep raising the pressure just to hold a steady speed, the brakes are fading, so slow down and drop to a lower gear.

Answer

The governor has cut out

Answer

The tanks are overfilled

Answer

The alcohol evaporator is empty

Question 3

What is the main reason water must be removed from the air tanks?

Accepted Answer

Trapped water can freeze in cold weather and disable the brakes — Moisture and compressor oil collect in the tanks, and the water can freeze and knock out the brakes, so it must be cleared out.

Answer

It lowers the boiling point of the brake fluid

Answer

It keeps the alcohol evaporator from overflowing

Answer

It stops the governor from cutting out too early

Question 4

What is the function of a slack adjuster?

Accepted Answer

It compensates for wear of the brake shoes — A slack adjuster takes up the extra play that develops as the brake shoes wear.

Answer

It stores extra compressed air for emergencies

Answer

It warns the driver of low air pressure

Answer

It drains moisture from the tanks

Question 5

Where is the safety relief valve placed, and what is its job?

Accepted Answer

In the first reservoir the compressor charges, where it guards against too much pressure — It sits in the first reservoir the compressor charges and guards the whole system against excess pressure.

Answer

In the last tank in the line, where it warns of low pressure

Answer

On the brake pedal, where it limits how hard you can press

Answer

At each wheel, where it keeps the brakes from locking

Question 6

If the safety valve lets air escape, what does that tell you?

Accepted Answer

There is a fault that a mechanic should repair — Venting air means something is wrong in the system, and a mechanic should correct it.

Answer

The system is fine and no action is needed

Answer

Tank pressure is simply at its normal level

Answer

The alcohol evaporator needs refilling

Question 7

Older vehicles had a front brake limiting valve with a 'normal/slippery' control. What did the 'slippery' setting do?

Accepted Answer

It reduced the front-brake air pressure by half — In the 'slippery' position the limiting valve cut the normal air pressure sent to the front brakes in half.

Answer

It doubled the pressure to the front brakes

Answer

It shut off the rear brakes completely

Answer

It engaged the spring brakes

Question 8

What does the supply pressure gauge tell the driver?

Accepted Answer

The amount of air pressure stored in the tanks — The supply pressure gauge reports how much air is stored in the tanks.

Answer

How much pressure is being applied to the brakes

Answer

The temperature of the brake drums

Answer

Whether the parking brake is set

Question 9

At roughly what pressure does the governor shut the air compressor off?

Accepted Answer

Somewhere between about 120 and 140 psi — The 'cut-out' point, where the governor stops the compressor, falls in the 120 to 140 psi range.

Answer

Around 100 psi

Answer

Around 60 psi

Answer

Right at 150 psi

Question 10

What is true about front-wheel braking on a commercial vehicle?

Accepted Answer

Front-wheel braking helps in all conditions and rarely causes skids, even on ice — Front-wheel braking helps in every condition, and braking-induced front skids are unlikely even on ice.

Answer

Front brakes should be disabled on wet roads

Answer

Front brakes are only useful on dry pavement

Answer

Front-wheel braking sharply raises the chance of a skid

Question 11

Where is the ABS malfunction lamp located on a trailer?

Accepted Answer

On the left side, at a front or rear corner — A trailer's ABS malfunction lamp is on the left side, at either the front or the rear corner.

Answer

On the rear bumper at the center

Answer

On the instrument panel inside the cab

Answer

Behind the tractor's grille

Question 12

How does an air-operated disc brake differ from an s-cam brake?

Accepted Answer

It uses a power screw rather than an s-cam to squeeze the rotor — An air disc brake uses a power screw instead of an s-cam to clamp the rotor between the caliper pads.

Answer

It has no slack adjuster at all

Answer

It runs on hydraulic fluid instead of air

Answer

It works without any brake chamber

Safe Driving Practices

Study questions with answers

1. A safety relief valve is usually set to release air at what pressure?

2. On a vehicle with an application pressure gauge, needing more and more pressure to hold the same speed is a sign of what?

3. What is the main reason water must be removed from the air tanks?

4. What is the function of a slack adjuster?

5. Where is the safety relief valve placed, and what is its job?

6. If the safety valve lets air escape, what does that tell you?

7. Older vehicles had a front brake limiting valve with a 'normal/slippery' control. What did the 'slippery' setting do?

8. What does the supply pressure gauge tell the driver?

9. At roughly what pressure does the governor shut the air compressor off?

10. What is true about front-wheel braking on a commercial vehicle?

11. Where is the ABS malfunction lamp located on a trailer?

12. How does an air-operated disc brake differ from an s-cam brake?

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