When operating a set of doubles, the shut-off valves at the rear of the first trailer should be in their: Question When operating a set of doubles, the shut-off valves at the rear of the first trailer should be in their: Answers Lifted position. Closed position. Open position. Explanation When operating a double or triple, the shut-off valves at the rear of last trailer should be closed. All other shut-off valves should be open. This questions appears in the following tests: Kentucky Double New Mexico Double