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What is a modulated (spring brake) control valve on some older vehicles used for?
- A.It adjusts the radio volume in steps
- B.It lets the driver gradually apply the spring brakes by hand for emergency stopping control
- C.It meters fuel to the compressor
- D.It locks the steering column
Correct answer
B. It lets the driver gradually apply the spring brakes by hand for emergency stopping control
Why
The modulated valve gives graduated hand control of the springs so an emergency stop can be managed rather than all-or-nothing. Most modern trucks instead rely on the automatic application plus careful service brake use as pressure allows.
Manual topic: Air Brakes - Spring Brakes and Parking Brakes · From the Air Brakes practice bank (AB-112).