What will be the effect of disconnecting the power cable of a trailer with two-circuit pneumatic braking system from a tractor?
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Correct answer
A. The switching on of the trailer's brakes.
Explanation
In the photo, there is a blue agricultural tractor with a red two-axle trailer connected. Disconnecting the supply line of a trailer with a two-circuit air brake system will apply the trailer's brakes - answer A.
The trailer valve treats a drop in pressure in the supply line (red) as a failure and applies the trailer's brakes using the air stored in its tank. The rules require the trailer's service brake to stop it automatically if the connection with the towing vehicle breaks - a torn line must not leave a moving trailer without brakes. Switching off the brakes (answer B) would contradict this principle, and answer C ignores the purpose of the whole system. The practical consequence: after the red line is disconnected, the trailer is braked, but not forever, because the air gradually escapes. That is why, when you leave a trailer, you always apply its parking brake, and on a slope you put chocks under the wheels.
Legal basis: § 48 para. 2 point 1 letter b and point 2 of the Regulation on the technical conditions of vehicles and the scope of their necessary equipment