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Questions and Answers
What is a dual air brake system?
What is a dual air brake system?
A dual air brake system has two separate air brake systems, which use a single set of brake controls. One system operates the regular brakes on the rear axle, while the other operates the brakes on the front axle.
What are the slack adjusters?
What are the slack adjusters?
Slack adjusters regulate the distance that the air brake has to travel to apply friction to the wheel, compensating for wear on the brake shoe.
How can you check slack adjusters?
How can you check slack adjusters?
Park on level ground, release the parking brakes, and pull hard on each slack adjuster. If it moves more than one inch at the push rod attachment, it needs adjustment.
How can you test the low pressure warning signal?
How can you test the low pressure warning signal?
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How can you check that the spring brakes come on automatically?
How can you check that the spring brakes come on automatically?
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What are the maximum leakage rates for air brake systems?
What are the maximum leakage rates for air brake systems?
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Study Notes
Dual Air Brake System
- Comprises two separate air brake systems operated by a single set of controls.
- Each system has independent components: air tanks, hoses, and lines.
- Typically, one system controls the brakes on the rear axle(s), while the other handles the front axle (and possibly one rear axle).
- Both systems provide air to any attached trailer.
- Designated as "primary" for the first system and "secondary" for the second.
Slack Adjusters
- Control the distance that air brakes travel to apply friction to the wheel.
- As brakes wear, this distance increases due to the erosion of the brake shoe's friction material.
Checking Slack Adjusters
- Perform checks on S-cam brakes while parked on level ground with chocked wheels.
- Must release parking brakes to assess slack adjusters.
- A slack adjuster should not move more than one inch at the push rod attachment point; excessive movement indicates a need for adjustment.
- Properly adjusted brakes are crucial; excessive slack can hinder stopping effectiveness.
- Brake misadjustments are common issues discovered during roadside inspections.
Low Pressure Warning Signal Test
- To test, shut off the engine when air pressure is sufficient for the warning signal to remain off.
- Engage electrical power and alternately depress the brake pedal to reduce air tank pressure.
- The low pressure warning signal should activate before the pressure drops below 60 psi in the tank with the lowest pressure.
Automatic Spring Brake Activation Check
- To check spring brakes, reduce air pressure by repeatedly stepping on and off the brake pedal.
- The tractor protection valve and parking brake valve should engage (pop out) when air pressure drops to specified levels (20 - 45 psi).
- Activation of these valves signals that the spring brakes are engaging automatically.
Maximum Leakage Rates
- For single vehicles, the maximum allowable leakage rate is less than 2 PSI within one minute.
- For combination vehicles, the rate should be less than 3 PSI in one minute.
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Description
Test your knowledge on dual air brake systems with these flashcards covering CDL subsections 5.2 and 5.3. Each card provides concise definitions and key concepts critical for understanding how air brake systems operate in vehicles. Prepare effectively for your CDL exam by mastering these essential topics.
