What is the general purpose of a relay valve on a vehicle with a long distance between the brake pedal's air signal and the rear brakes?

Pick an answer

1. It is only found on vehicles without trailers, serving no purpose on combination rigs since the trailer handles its own air supply
2. It stores extra air only for the horn and other accessories, not for braking
3. It reduces how much braking force reaches the rear axles compared to the front
4. It speeds up brake application at the rear axles by supplying air locally instead of waiting for it to travel the full length of the vehicle

Correct!

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