Practice question

What happens to the trailer brakes if the supply (emergency) line breaks?

The trailer service brakes apply using the tractor foot pedal only
The tractor protection valve closes, and the trailer emergency spring brakes apply immediately
The air compressor switches to fast-pumping mode to compensate
The tractor rear brakes lock up while the trailer continues to roll

Answer: B — The tractor protection valve closes, and the trailer emergency spring brakes apply immediately

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