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CDL · Air Brake Parts

What is the foot valve (treadle valve) in an air brake system?

Reviewed by Jordan Morley, Editorial Lead at 247SimpleTests. Written by the 247SimpleTests Editorial Team from the official source material cited on every question.

Correct answer

The brake pedal mechanism that controls how much air pressure is applied to the service brakes when the driver presses it

  1. A A valve for the tires
  2. B The fuel pedal
  3. C The brake pedal mechanism that controls how much air pressure is applied to the service brakes when the driver presses it
  4. D A parking device

Why this is the answer

The FOOT VALVE (also called the treadle valve or brake pedal) is the mechanism the driver operates with their foot to apply the SERVICE BRAKES. CDL air brakes. Pressing the foot valve releases compressed air to the brake chambers — the harder you press, the more air pressure (application pressure) is delivered and the more braking force is produced; releasing it lets the air out and releases the brakes. The foot valve controls normal service braking.

Other controls: the parking brake control (knob for spring brakes); the trailer hand valve/trolley valve (applies only trailer brakes — for testing, not parking). Knowing the foot valve is the service brake pedal that controls application pressure is commonly tested air brake system knowledge.

Source: FMCSA CDL Manual — Air Brakes, Foot Valve

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About this topic: Air Brake Parts

Knowing the parts of the air brake system — compressor, governor, supply tank, dryer, slack adjusters, spring brakes — is required so you can recognize defects during inspection. This is one of 22 Air Brakes questions on air brake parts, each with a full explanation on a single study page.

New to this exam? Our CDL exam guide explains the format, scoring, and how to prepare.

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