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Air Brake System Parts — CDL Air Brakes Practice Test

Air Brake System PartsQuestion 1 of 30

33 questions in this topic · 30 drawn at random this round

At about what pressure is the safety valve usually set to open?

CDL Manual — Air Brakes

Questions are based on the official CDL manual (AAMVA model) used by state DMVs. The real CDL knowledge test is given in English — federal rules (FMCSA, 49 CFR 391.11) require English proficiency to drive commercially; our Chinese & Spanish are study aids. Some states also offer the written test in other languages (see the per-state table).

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This CDL Air Brakes Air Brake System Parts practice set has 33 practice questions based on the official exam materials, each with an instant explanation. You need 80% on the real CDL Air Brakes knowledge test to pass.

Sample questions

Three questions from the Air Brake System Parts bank with the correct answer and an explanation. The practice quiz above draws 30 questions at random from the same bank.

  1. What is the job of the air compressor in an air brake system?

    • It pumps air into the air storage tanks — Correct answer
    • It releases air from the tanks to apply the brakes
    • It removes water and oil from the air tanks
    • It warns the driver when air pressure is low

    Explanation: The air compressor pumps air into the air storage tanks (reservoirs); it is connected to the engine through gears or a v-belt. English term: air compressor（空气压缩机 / compresor de aire）.

    Handbook: Air Brake System Parts — Air Compressor

  2. If the air compressor has its own oil supply, what should you do before driving?

    • Check the compressor's oil level — Correct answer
    • Drain the oil out of the compressor
    • Add alcohol to the compressor
    • Disconnect the compressor from the engine

    Explanation: Some compressors have their own oil supply and others are lubricated by engine oil; if the compressor has its own oil supply, check the oil level before driving. English term: air compressor（空气压缩机 / compresor de aire）.

    Handbook: Air Brake System Parts — Air Compressor

  3. What does the governor control in an air brake system?

    • When the air compressor pumps air into the storage tanks — Correct answer
    • How much air pressure goes to the front brakes
    • When the brake lights come on
    • When the spring brakes release

    Explanation: The governor controls when the air compressor will pump air into the air storage tanks. English term: governor（调压器 / regulador）.

    Handbook: Air Brake System Parts — Air Compressor Governor