Mixed Deck — All Air Brake Test Topics Flashcards

What is the normal air pressure operating range for a commercial vehicle air brake system?

Answer: 100–125 psi

The air brake system is designed to operate between approximately 100 psi (cut-in) and 125 psi (cut-out), the range maintained by the governor.

Why is it important to drain air tanks daily?

Answer: To remove water and prevent rust

Compressed air naturally contains moisture, which condenses into water inside the air tanks. Draining the air tanks daily is essential to remove this accumulated water and any oil contaminants. This practice prevents rust and corrosion within the air brake system, which can lead to component failure, reduced braking efficiency, and costly repairs.

What is the purpose of the wet tank (supply tank) in a dual air brake system?

Answer: To receive air first from the compressor and collect moisture and oil before air passes to the primary and secondary tanks

The wet tank receives air directly from the compressor and is the collection point for moisture and oil. Air then passes through a check valve into the primary and secondary supply tanks.

Why can a fully loaded truck sometimes require more stopping distance than an empty truck?

Answer: Greater mass means more kinetic energy must be dissipated during braking

Greater vehicle mass means significantly more kinetic energy at the same speed, requiring more braking force and distance to stop.

What is the lowest pressure at which the governor should trigger the compressor to resume its pumping phase?

Answer: 80 psi (552 kPa).

The air brake system's governor is designed to control the compressor's operation, ensuring adequate air pressure. It should trigger the compressor to resume pumping air into the reservoirs when the pressure drops to approximately 80 psi (552 kPa). This 'cut-in' pressure ensures that there is always sufficient air for safe braking, preventing the pressure from falling too low.

Per air brake instructions, what is the proper following distance increase in bad weather or poor traction?

Answer: Increase the following distance

Poor traction and bad weather require increasing your following distance for safe stopping.

What is the effect on air brake performance if the air tanks are not drained regularly?

Answer: Water accumulates and can freeze in cold weather, blocking air lines and causing brake failure

Water that accumulates in undrained air tanks can freeze in cold temperatures, blocking air lines and brake valves, potentially causing complete brake failure.

How does wet pavement affect the stopping distance of a vehicle with air brakes?

Answer: Wet pavement can double the stopping distance compared to dry pavement

Wet pavement significantly reduces tire-to-road friction, which can approximately double the stopping distance compared to dry conditions.

Why do hydraulic brakes stop more quickly than air brakes?

Answer: It takes longer for the air to flow through the lines

Hydraulic brakes generally stop more quickly than air brakes because hydraulic fluid is incompressible and transmits force almost instantly through the lines. Air, being compressible, takes a fraction of a second longer to travel through the lines and build pressure in the brake chambers, resulting in a slight delay compared to hydraulic systems.

What does the air pressure gauge in the cab show the driver?

Answer: The amount of pressure in the air tanks

The gauge displays the air pressure available in the reservoir tanks.

Which gauge tells you the air pressure available for braking?

Answer: Air pressure gauge

The air pressure gauge is a critical instrument located on the dashboard that displays the amount of compressed air available in the air tanks. Drivers must constantly monitor this gauge to ensure there is sufficient air pressure for safe braking and to detect any potential leaks or malfunctions in the air brake system. It provides real-time feedback on braking capability.

What is the primary function of an antilock braking system (ABS) on an air brake vehicle?

Answer: To automatically prevent wheel lockup, allowing the driver to steer while braking hard

ABS modulates brake pressure at each wheel to prevent lockup, preserving the driver's ability to steer during hard stops.

Which statement about automatic slack adjusters is TRUE?

Answer: They still require periodic inspection to verify they are functioning correctly

Even though automatic slack adjusters adjust on their own during braking, drivers must still inspect them during pre-trip checks to verify they are working properly and not damaged.

What causes glazed brake linings and how does glazing affect braking performance?

Answer: Overheating from excessive braking — creates a hardened, low-friction surface that reduces stopping power

Overheated brake linings develop a glassy, hardened surface with significantly reduced friction coefficient, weakening braking force.

What type of pressure holds the parking or emergency brakes on trucks and buses in place?

Answer: Spring pressure

In air brake systems, the parking or emergency brakes are held in place by powerful springs, not air pressure. Air pressure is actually used to compress these springs, releasing the brakes. When air pressure is lost or released by the driver, the springs expand, applying the brakes automatically as a fail-safe mechanism.

What is one of the key tasks during the pre-trip inspection of the air brake system?

Answer: Check that the air pressure is within the correct range and the air gauge is working.

A key task during the pre-trip inspection is to verify that the air pressure in the system falls within the manufacturer's specified operating range. This ensures there is adequate air supply for safe braking. Additionally, checking that the air gauge itself is working accurately is crucial, as it provides the driver with vital information about the system's status during operation.

Which pedal does a driver press to apply the air brakes?

Answer: Brake pedal

The brake pedal is the primary control that a driver presses to apply the service brakes in an air brake system. When pressed, it signals the system to release compressed air to the brake chambers at each wheel, initiating the braking action. This direct interface allows the driver to control the vehicle's deceleration and stopping power.

How does the air pressure regulation system contribute to overall safety?

Answer: By maintaining proper air pressure, ensuring safe braking and operation.

The air pressure regulation system contributes significantly to overall safety by maintaining proper air pressure, which is fundamental for safe braking and operation. By ensuring consistent and correct pressure, it prevents both weak braking due to insufficient air and component damage from excessive pressure. This reliable control over braking power is crucial for preventing accidents and ensuring vehicle stability.

What component stores compressed air for braking?

Answer: Air tank

The air tank, also known as a reservoir, is a crucial component in an air brake system responsible for storing compressed air. This stored air is then used to actuate the brakes when the driver applies the brake pedal, ensuring a constant and sufficient supply of air pressure for effective braking. Without air tanks, the system would not have the necessary pressure reserve.

Which three components combine to make up the total stopping distance for a truck with air brakes?

Answer: Perception/reaction distance + brake lag distance + actual braking distance

Total stopping distance is the sum of how far the truck travels during perception/reaction, during brake lag, and during actual braking.