Practice question

What is the purpose of the tractor protection valve or supply valve in relation to a bus towing a trailer?

To increase the air pressure to the trailer brakes
To protect the bus's air brake system by shutting off air flow to the trailer if a leak occurs in the trailer lines
To control the slack adjusters on the trailer
To prevent the trailer from jackknifing during braking

Answer: B — To protect the bus's air brake system by shutting off air flow to the trailer if a leak occurs in the trailer lines

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