CDL Air Brakes TestInspecting Air Brake SystemsMedium
During a pre-trip inspection, a driver checks the spring brakes. Which of the following statements is true regarding the function of spring brakes?
- ASpring brakes are engaged by air pressure and released by mechanical force.
- BSpring brakes are designed to be used as the primary service brakes.
- CSpring brakes are primarily used for emergency braking only.
- DSpring brakes apply when air pressure drops to a dangerous level or is released by the driver.
Show answer & explanationAnswer & explanation
Correct answer: D. Spring brakes apply when air pressure drops to a dangerous level or is released by the driver.
Spring brakes are held in the 'released' position by air pressure. When air pressure drops below a safe level (typically 20-45 psi) or when the driver pulls the parking brake control, the springs expand and apply the brakes.
Why the other options are wrong
- A. This is incorrect; spring brakes are released by air pressure and applied by spring force.
- B. Spring brakes are for parking and emergency, not for routine service braking.
- C. While they act as emergency brakes, they also serve as parking brakes.
Spring Brake Function
Spring brakes are a safety feature that applies the vehicle's brakes automatically when air pressure drops to a critical level or when the parking brake is engaged.
- Held 'off' by air pressure.
- Apply automatically when air pressure drops below 20-45 psi.
- Used for parking and emergency braking.
- Are powerful and can lock wheels.
Memory trick: Springs pop, air drops, brakes lock!