Pennsylvania CDL: Air Brakes Practice Test

Not quite. The answer is The dashboard air pressure gauges won't drop when it's drained.

It may be difficult to visually identify the supply tank. Instead, remember that your dashboard air pressure gauges monitor the air pressure in the primary and secondary service tanks. (In some vehicles, there are two gauges, one for each service tank; in other vehicles, there is one gauge with two needles.) Draining the service tanks will cause the gauges to show a drop in air pressure in those tanks. The supply tank is the tank that does NOT drop the gauges when it's drained.

Not quite. The answer is Stop and park safely.

If the low air pressure warning comes on, there may be a leak in the system. Pull over and park your vehicle as soon as possible. If the air pressure drops too low, the spring brakes will come on automatically, which will stop your vehicle – but not necessarily in a safe way. Sudden application of the spring brakes while you're driving might result in a skid.

Not quite. The answer is 100 psi.

A dual air brake system has two separate air brake systems. Typically, the primary system operates the brakes on the rear axle(s), and the secondary system operates the brakes on the front axle (and possibly one rear axle). Before driving a vehicle with a dual air brake system, let the air compressor build up a minimum of 100 psi pressure in each of the two brake systems.

Not quite. The answer is glad hands

As part of your vehicle inspection test, if your vehicle is equipped with air brakes and has a trailer, you will inspect the air connections between the truck or tractor and the trailer. These connections are made with hose couplers (commonly called "glad hands" because they vaguely resemble shaking hands). These glad hands have rubber seals to form a tight connection and prevent air from escaping. Make sure that the glad hands are locked in place and free of damage or air leaks.

Not quite. The answer is All vehicles with air brakes currently in operation must have low air pressure warning signals.

All vehicles on the road that have air brakes must have low air pressure warning signals.

Not quite. The answer is Brake firmly while slowly moving forward on level ground.

To test the service brakes, wait to build up normal air pressure. Then move your vehicle forward slowly (at about 5 mph) and brake hard. Check whether your vehicle stops promptly without pulling to one side or the other.

Not quite. The answer is They are not as strong as service brakes.

Spring brakes start to drag as pressure drops to about 60 psi, and they release as pressure rises to about 60 psi. Yet a full service brake application can be 100 psi. The coil spring in most spring parking brake chambers can exert a force of between 1,500 and 2,000 pounds. With a full service brake application of 100 psi, a typical Type 30 brake chamber can produce a force of 30 × 100 = 3,000 pounds.

Not quite. The answer is Park on level ground. Chock the wheels. Release the parking brake when you have enough air pressure. Shut off the engine. Repeatedly press and release the brake pedal.

To test whether the spring brakes come on, release the parking brake (all vehicles), release the tractor protection valve control (on combination vehicles), and turn off the engine while leaving the electrical power on to power the instrument panel. Then step on and off the brake pedal. The low air pressure warning signal should come on when the pressure has fallen below 55 psi. Continue stepping on and off the brake pedal until you reach about 20–45 psi, at which point the parking brake valve should close or pop out.

Not quite. The answer is 3 psi in one minute.

When testing for an air leak, make sure the system is fully charged, turn off the engine, fully apply the foot (service) brake, and hold the brake for one minute. The air pressure should not drop more than 3 psi for a single vehicle or more than 4 psi for a combination vehicle. If it does, check for an air leak somewhere.

Not quite. The answer is either (a) or (b).

If you need to stop quickly, use either the "controlled braking" method or the "stab braking" method. However, if your vehicle has antilock brakes, stab braking won't work because the wheels won't lock. Use controlled braking instead.

Not quite. The answer is brake drum.

In North America, the most common type of foundation brake is the S-cam drum brake. The brake shoes and linings press against the inside of the brake drum, which causes friction to slow the wheel.

Not quite. The answer is With ABS, you do emergency braking differently than without ABS.

Without ABS, hard braking can lock the wheels, resulting in a skid. Therefore, to do emergency braking without ABS, you should use the "stab braking" method or the "controlled braking" method. With ABS, go ahead and brake hard; the ABS computer will prevent your wheels from locking.

Not quite. The answer is Between the air compressor and the supply ("wet") tank

The supply ("wet") tank tends to get most of the moisture because moisture condenses there as the hot air from the compressor cools. To help alleviate this situation, the air dryer dries the air from the compressor before it enters the supply tank. Note: Today's air dryer technology is so effective that a "wet" tank may not be needed anymore. In a modern Air Dryer Integrated System (ADIS), air from the air dryer goes directly into the primary and secondary service ("dry") tanks.

Not quite. The answer is (b) Spring brake priority

Instead of providing air pressure to both the service brakes and the spring brakes at the same time, trailer brake subsystems give priority to one or the other. Trailers with spring brake priority supply compressed air to the spring brakes (to release them) before the service tanks have filled. Trailers with service brake priority fill the service tanks before supplying air to the spring brakes. When coupling your tractor to a trailer with service brake priority, you must wait until the service tanks are full before you can release the trailer's parking brakes. Trailers more than 25 years old were more likely to implement service brake priority. Today's modern trailers are more likely to implement spring brake priority. Ask your employer or a qualified person whether your trailer uses spring brake priority or service brake priority.

Not quite. The answer is the service brake valve and the parking brake valve.

A spring parking brake can exert a force of up to 2,000 pounds, and a Type 30 service brake chamber can exert a force of 3,000 pounds or more. If both forces were applied at the same time (which is called compounding the service and parking brakes), the combined force could damage parts of the braking system. To prevent this, most modern commercial vehicles employ an anti-compounding valve. One input port of this valve is connected to the service brake valve (foot valve), and another input port is connected to the parking brake valve (yellow knob). Suppose you set the parking brakes by pulling out the yellow knob. That valve will send air to the anti-compounding valve. If you also press the brake pedal, the foot valve will also send air to the anti-compounding valve. Then the anti-compounding valve will partially release the parking brakes by the same amount of force that the foot valve has applied.

Not quite. The answer is 55 to 60 psi.

A low pressure warning signal visible to the driver must come on before the pressure in the service air tank falls below 55 psi (or one-half the air compressor governor cutout air pressure on older vehicles).

Not quite. The answer is Use gloves and pull hard on each slack adjuster you can reach.

To check the slack adjusters, try to pull on them manually while wearing gloves. If there is an inch or more of "give," there is an issue and they should be fixed.

Not quite. The answer is Whenever your vehicle is parked

You should always use your parking brake except when the brakes are very hot or they are wet and at risk of freezing.

Not quite. The answer is by increasing and decreasing the air pressure.

The air compressor governor should cut in when a lower air pressure is reached and cut out when a higher air pressure is reached. (Check your manufacturer's specifications for these pressures.) To test this, run the engine at a fast idle to raise the air pressure until the air compressor governor cuts out. Then keep stepping on and off the brake pedal to reduce the air pressure until the air compressor governor cuts in.

Not quite. The answer is slack adjuster; brake camshaft

To apply the S-cam drum brakes, air is let into each brake chamber. Air pressure pushes the pushrod out, moving the slack adjuster, thus rotating the brake camshaft. As the S-cam on the camshaft rotates, it forces the brake shoes against the inside of the brake drum.