In a set of triples, the shut-off valves at the rear of the middle trailer should be: Before you start the test, please answer the question below regarding your insurance status. Without insurance you will not be able to drive in Ohio Do you currently have car insurance? Yes I have insurance. Great, you're all set! Click here if you still want to compare rates. No, I need insurance and I want to compare options. Question In a set of triples, the shut-off valves at the rear of the middle trailer should be: Answers Removed. Closed. Polished. Open. Explanation When operating a double or triple, the shut-off valves at the rear of the last trailer should be closed. All other shut-off valves should be open. This questions appears in the following tests: Pennsylvania Double South Carolina Double