Mixed Deck — All CDL AIR BRAKE Topics Flashcards

What does the supply pressure gauge in the cab indicate?

Answer: The current air pressure available in the storage tanks

The supply pressure gauge shows the driver the current air pressure in the tanks so they know if adequate braking power is available.

What should you do if your low air pressure warning activates?

Answer: Stop immediately and safely park the vehicle.

If the low air pressure warning activates, it indicates a critical issue with the air brake system, meaning there might not be enough air to safely operate the brakes. Continuing to drive risks complete brake failure, so the safest and most responsible action is to immediately and safely stop the vehicle to prevent an accident.

When inspecting the air brake system during a pre-trip, what should you check regarding the air compressor?

Answer: All of the above.

During a pre-trip inspection, it's crucial to thoroughly check the air compressor. This includes verifying that it is securely mounted, free from any visible damage or leaks, and operating correctly. You must confirm that it builds and maintains air pressure within the specified range by turning on and off automatically, ensuring the entire air brake system is functional.

What is the primary purpose of ABS on a vehicle?

Answer: To prevent wheel lock-up during hard braking.

The primary purpose of ABS (Anti-lock Braking System) is to prevent the wheels from locking up during hard braking. This allows the driver to maintain steering control and vehicle stability, especially on slippery surfaces. While it can sometimes reduce stopping distances, its main function is to prevent uncontrolled skidding and improve control.

What should you do if the ABS warning light stays on after you start your vehicle?

Answer: Get the ABS checked as soon as possible, but the service brakes will still work.

If the ABS warning light stays on, it indicates a malfunction in the Anti-lock Braking System. While the ABS itself may not be working, the vehicle's regular service brakes will still function normally, allowing you to stop. It is important to get the ABS checked by a mechanic as soon as possible to restore this important safety feature, but it does not require an immediate stop or tow.

Some vehicles are equipped with a control lever on the dash that allows the driver to apply the spring brakes gradually. What is this control called?

Answer: A modulating control valve.

A modulating control valve allows the driver to control the application of the spring brakes, typically through a lever on the dash. This provides a 'feel' for the braking action and allows for a controlled stop if the service brakes fail.

What is brake lag distance in an air brake system?

Answer: The distance traveled while air pressure builds up to physically apply the brakes after the pedal is pressed

Brake lag is the distance the vehicle travels while air pressure builds to actually apply the brakes after the pedal is pressed, which can be up to 0.4 seconds.

Why does total stopping distance increase significantly on downgrades compared to level roads?

Answer: Gravity continuously accelerates the vehicle, adding to momentum and requiring more distance to stop

On downgrades, gravity continuously accelerates the vehicle, increasing its momentum and requiring a much greater stopping distance.

In a typical dual air brake system on a two-axle truck, how are the two systems usually split?

Answer: One system operates the front axle, and the other operates the rear axle.

Typically, the primary system operates the brakes on the rear axle(s), and the secondary system operates the brakes on the front axle. This separation ensures that if one system fails, the other can still provide braking on at least one axle.

When testing the air compressor governor, what are the typical cut-in and cut-out pressures?

Answer: Cut-in at 100 psi, cut-out at 125 psi

The air compressor governor is typically set to cut-in (start pumping air) at around 100 psi and cut-out (stop pumping air) at around 125 psi. This ensures the air tanks stay within the proper operating range.

How is the air compressor typically driven on a commercial vehicle?

Answer: By the vehicle's engine via belt or gear

The air compressor is driven by the vehicle's engine through a belt or gear connection.

What is brake fade?

Answer: The loss of braking power caused by overheated brakes

Brake fade occurs when brakes overheat, causing a significant loss of braking effectiveness that can be extremely dangerous on long downgrades.

How do you check for leaks in the air brake system?

Answer: Apply full brake pressure, turn off the engine, release the brakes, and watch the pressure gauge.

To properly check for leaks in the air brake system, you should build up full air pressure, then turn off the engine. With the engine off, apply the service brakes fully for one minute and observe the air pressure gauge. A drop of more than 3 psi for single vehicles or 4 psi for combination vehicles indicates a leak that needs to be addressed.

What is the purpose of one-way check valves between air tanks?

Answer: To prevent pressure loss in one tank if another tank develops a leak

One-way check valves prevent air from flowing backward, protecting pressure in each tank if another develops a leak.

When should you avoid using the parking brake?

Answer: When the brakes are hot after a long descent.

Applying the parking brake when the service brakes are hot, especially after a long descent, can cause the brake drums or rotors to warp as they cool unevenly. It can also cause the brake linings to stick to the drums or rotors, potentially damaging the brake system. It's safer to allow hot brakes to cool down before engaging the parking brake.

What is the primary purpose of the safety relief valve on an air tank?

Answer: To release air if the tank pressure gets too high

The safety relief valve is designed to open and release air if tank pressure exceeds a safe level, protecting the system from over-pressurization.

Which air tank is the first to receive compressed air from the compressor?

Answer: Supply (wet) tank

The supply tank, also called the wet tank, is the first tank air enters after leaving the compressor, where it loses much of its moisture.

How does brake fade affect stopping distance?

Answer: Stopping distance increases significantly as brakes overheat

As brakes overheat and fade, stopping distance can increase dramatically, making it impossible to stop within a safe distance.

During a pre-trip inspection, you notice that the spring brakes do not automatically apply when the air pressure drops to the 20-45 PSI range. This indicates a problem with the:

Answer: Parking brake control valve.

The parking brake control valve (often a yellow, diamond-shaped knob) is designed to pop out, causing the spring brakes to apply, when air pressure drops to a range between 20 and 45 PSI. If this doesn't happen, the valve may be faulty, creating a serious safety issue.

What is a 'brake spider' in an S-cam drum brake system?

Answer: The fixed mounting bracket attached to the axle that supports brake shoes and foundation brake components

The brake spider is the fixed mounting bracket attached to the axle flange that supports the brake shoes, anchor pins, and other foundation brake components.