Question:
When you're pulling doubles or triples, the shut-off valves should always be
A
open except for those on the last trailer.
explanation
Shut-off valves (also called "cut-out cocks") are used in the service and supply air lines at the back of trailers used to tow other trailers. These valves permit closing the air lines off when another trailer is not being towed. [Commercial Driver Handbook]
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