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Key Facts: Delaware CDL Air Brakes Exam

80%

Minimum passing score on CDL knowledge tests

49 CFR 383.135

Around 125 psi

Air compressor governor cut-out reference pressure

Delaware CDL Manual Section 5

100 psi

Typical air compressor governor cut-in pressure

Delaware CDL Manual Section 5

Before 55 psi

Low-air warning activation threshold

Delaware CDL Manual Section 5

20 to 45 psi

Air pressure range where spring brakes automatically apply

Delaware CDL Manual Section 5

150 psi

Safety valve pressure relief threshold

Delaware CDL Manual Section 5

Commercial drivers in Delaware must pass the Air Brakes knowledge test and demonstrate the air-brake inspection to operate an air-braked CMV without Restriction L. Current manual reference points include governor cut-in around 100 psi, cut-out around 125 psi, low-air warning before pressure falls below 55 psi, and spring-brake application between 20 and 45 psi.

Sample Delaware CDL Air Brakes Practice Questions

Try these sample questions to review concepts for the Delaware CDL Air Brakes exam. Each question includes a detailed explanation. Start the interactive quiz above for the full 170+ question experience with AI tutoring.

1Which component supplies compressed air to an air-brake vehicle's storage tanks?
A.The air compressor
B.The application pressure gauge
C.The slack adjuster
D.The spring-brake chamber
Explanation: The engine-driven air compressor pumps air into the storage tanks. The governor controls when the compressor loads and unloads, but it does not create the compressed air.
2In the current Delaware CDL Manual, at about what pressure does the governor cut out and stop the compressor from pumping?
A.About 100 psi
B.About 125 psi
C.About 55 psi
D.About 150 psi
Explanation: Section 5 says the governor normally cuts out at around 125 psi. It cuts back in around 100 psi when tank pressure falls.
3At about what tank pressure should the air-compressor governor cut in and resume pumping?
A.About 55 psi
B.About 125 psi
C.About 100 psi
D.About 150 psi
Explanation: The Delaware manual gives about 100 psi as the governor's cut-in pressure. Cut-in is the point at which the governor allows the compressor to begin pumping again.
4When must manually operated air-tank drains be opened?
A.Whenever pressure reaches governor cut-out
B.Once each week
C.Only when water appears at a brake chamber
D.At the end of each day of driving
Explanation: Water and compressor oil collect at the bottom of the tanks and can damage the system or freeze. The manual says to drain tanks with manual valves at the end of each day of driving.
5Your vehicle has an alcohol evaporator and manual tank drains. What cold-weather maintenance does the manual require?
A.Check and fill the alcohol container as needed each day, and continue draining the tanks daily
B.Fill the alcohol container weekly and stop draining the tanks
C.Drain the tanks only when the alcohol container becomes empty
D.Remove the evaporator once temperatures fall below freezing
Explanation: An alcohol evaporator reduces the risk of ice in valves and lines, so its container should be checked daily in cold weather. It does not remove water or oil from manual-drain tanks, which still require daily draining.
6What is the purpose of the safety valve in the first tank supplied by the air compressor?
A.To apply the spring brakes when pressure is low
B.To open at about 150 psi and protect the system from excess pressure
C.To drain water automatically at governor cut-out
D.To balance pressure between the primary and secondary gauges
Explanation: The safety relief valve protects the tank and the rest of the air system from excessive pressure. It is usually set to open at 150 psi; if it releases air, the fault needs mechanical repair.
7What happens when a driver presses the air-brake pedal farther down?
A.The governor raises its cut-out setting
B.The parking springs apply more strongly
C.More air pressure is sent to the service brakes
D.The compressor stops until the pedal is released
Explanation: The brake pedal is also called the foot valve or treadle valve. Pressing it farther applies more air pressure to the service brakes, while releasing it reduces pressure and exhausts some air.
8Which sequence correctly describes an S-cam brake application?
A.Air rotates the drum, which pulls the shoes inward through the pushrod
B.The slack adjuster pumps hydraulic fluid into a caliper
C.A wedge slides between the shoe ends without using a camshaft
D.Air moves the chamber pushrod and slack adjuster, rotating the S-cam so the shoes press the drum
Explanation: Air pressure moves the brake-chamber pushrod, which moves the slack adjuster and twists the camshaft. The S-shaped cam spreads the shoes against the inside of the brake drum.
9How does a wedge brake differ from an S-cam brake?
A.Its pushrod drives a wedge between the ends of the brake shoes
B.It uses a power screw to clamp pads on a rotor
C.It uses a rotating S-shaped cam to spread the shoes
D.It relies on a hydraulic wheel cylinder instead of an air chamber
Explanation: In a wedge brake, the chamber pushrod pushes a wedge directly between the ends of two brake shoes. The wedge forces the shoes outward against the drum without an S-camshaft.
10In an air-operated disc brake, what replaces the S-cam to create clamping force?
A.A wedge placed between two drum shoes
B.A power screw that clamps the rotor between caliper pads
C.A hydraulic master cylinder mounted at the wheel
D.A governor-driven ratchet on the hub
Explanation: Air-disc brakes use chamber and slack-adjuster movement to turn a power screw. That screw clamps the rotor between the lining pads of a caliper, much like a large C-clamp.

About the Delaware CDL Air Brakes Exam

Delaware treats air brakes as a knowledge and skills qualification tied to CDL restrictions, not as an endorsement. Passing the air-brakes knowledge test and demonstrating the air-brake inspection in an appropriately equipped skills-test vehicle avoids Restriction L (No Air Brakes Equipped CMV). This independent English-language multiple-choice practice bank studies Section 5 topics; it does not reproduce the DMV test interface or substitute for hands-on inspection practice.

Exam sponsor: Delaware Division of Motor Vehicles. The requirements and fees below concern the certification or admission exam, separate from our free practice resources.

Assessment

Walk-in CDL knowledge testing at Delaware DMV covers Section 5 (Air Brakes). Avoiding Restriction L also requires demonstrating the air-brake inspection and completing skills testing in an appropriately equipped vehicle; testing with air-over-hydraulic brakes results in Restriction Z.

Time Limit

No separate official time limit published by Delaware DMV or FMCSA for the Air Brakes knowledge test

Passing Score

At least 80% correct on each CDL knowledge test under FMCSA standards

Exam / Certification Fees

$10 commercial learner permit fee; $55 CDL issuance fee; $10 to remove a restriction after CDL issuance; no separate air-brakes knowledge-test fee is published

Exam sponsor website

Fees, eligibility, and exam policies can change. Confirm them with the exam sponsor before applying or paying.

Our practice resources: topics covered

We aim to reflect publicly available exam outlines and topic information in our study resources. Coverage, format, and difficulty may differ from the actual exam, and we cannot guarantee that every detail is accurate or current. Confirm exam requirements, fees, and policies with the official exam sponsor.

Delaware CDL Manual Section 5.1

Air Brake System Components and Operation

Air compressor, governor cut-in (around 100 psi) and cut-out (around 125 psi), air storage tanks, drain valves, safety valves (around 150 psi), foot valves, and foundation brakes.

Delaware CDL Manual Section 5.2

Dual Air Brake Systems and Gauges

Primary and secondary air systems, supply pressure gauges, application pressure gauges, and low-pressure warning devices that activate before pressure falls below 55 psi.

Delaware CDL Manual Section 5.1 & 5.2

Emergency, Parking, and Spring Brakes

Spring brakes held back by air pressure, mechanical spring application when pressure drops (20 to 45 psi), tractor protection valves, parking brake control knobs, and modulating valves.

Delaware CDL Manual Section 5.3

Inspecting Air Brake Systems

Step-by-step air brake check: static leakage test (<=2 psi/min single, <=3 psi/min combo), applied leakage test (<=3 psi/min single, <=4 psi/min combo), low-pressure buzzer check, spring brake pop-out test, and buildup rate.

Delaware CDL Manual Section 5.4

Using Air Brakes and Safe Driving Techniques

Normal stopping, emergency braking techniques (controlled braking vs stab braking), brake lag distance, brake fade, heat dissipation, and snub braking on steep downgrades.

Delaware CDL Manual Section 5.1 & FMCSA Rules

Anti-lock Braking Systems (ABS) and CDL Restrictions

ABS requirements and yellow malfunction lamps, how ABS aids vehicle stability, and Delaware/FMCSA air brake restrictions (Restriction L and Restriction Z).

Preparing for the Delaware CDL Air Brakes Exam

What You Need to Know

  • Passing score: At least 80% correct on each CDL knowledge test under FMCSA standards
  • Assessment: Walk-in CDL knowledge testing at Delaware DMV covers Section 5 (Air Brakes). Avoiding Restriction L also requires demonstrating the air-brake inspection and completing skills testing in an appropriately equipped vehicle; testing with air-over-hydraulic brakes results in Restriction Z.
  • Time limit: No separate official time limit published by Delaware DMV or FMCSA for the Air Brakes knowledge test
  • Exam / certification fees: $10 commercial learner permit fee; $55 CDL issuance fee; $10 to remove a restriction after CDL issuance; no separate air-brakes knowledge-test fee is published Official sources

Using Our Practice Resources

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Delaware CDL Air Brakes: Suggested Study Strategy

1Learn the current manual's reference pressures: cut-out around 125 psi, cut-in around 100 psi, safety valve around 150 psi, low-air warning before 55 psi, and spring-brake application between 20 and 45 psi.
2Practice the full in-cab air-brake inspection sequence using the examiner's current instructions and the vehicle manufacturer's specifications.
3Know the maximum acceptable leakage rates cold: 2 psi/min (static single), 3 psi/min (static combo), 3 psi/min (applied single), and 4 psi/min (applied combo).
4Understand mechanical components: S-cam, pushrod, slack adjuster, brake chamber, and brake shoes.
5Understand brake lag: air brakes take approximately one-half second or more for air to flow through the lines, adding 32 feet of stopping distance at 55 mph before the brakes begin slowing the vehicle.
6Remember that ABS prevents wheel lockup during hard braking but does not necessarily shorten stopping distance on all road surfaces.

Frequently Asked Questions

Is Air Brakes considered an endorsement or a restriction on a Delaware CDL?

Air Brakes is a knowledge requirement and restriction removal, not an endorsement. If an applicant does not pass the air brake knowledge test or takes the skills test in a vehicle without air brakes, Delaware DMV places Restriction L (No Air Brakes Equipped CMV) on the license.

At what pressures should the air compressor governor cut out and cut in?

The current Delaware manual uses approximately 125 psi for governor cut-out and approximately 100 psi for cut-in. A vehicle's manufacturer specifications remain controlling during an inspection.

When must the low air pressure warning device activate?

The current Delaware manual states that the warning must activate before pressure falls below 55 psi in either system. Large buses commonly warn at 80 to 85 psi.

What are the acceptable air leakage rates during an in-cab air brake test?

With the engine off and brakes released (static test), leakage must not exceed 2 psi per minute for a single vehicle or 3 psi per minute for a combination vehicle. With the service brake fully applied, leakage must not exceed 3 psi per minute for a single vehicle or 4 psi per minute for a combination vehicle.

At what air pressure do spring parking brakes automatically pop out and apply?

When air pressure drops below a safe level, typically between 20 and 45 psi, the spring brake control valve (tractor protection valve) will pop out, causing the powerful mechanical springs to apply the brakes automatically.

What is proper snub braking technique on a long downgrade?

In a proper low gear, apply brakes firmly enough to slow the vehicle down to 5 mph below your safe speed, release the brakes completely, allow speed to climb back up to your safe speed, and repeat. This technique prevents excessive heat accumulation and dangerous brake fade.