Refrigeration system isolation valves are specially designed with a back-seat, as well as a front-seat. For what purpose are these valves designed in this way?

Correct Answer: Option C — permit repacking the valve stem under pressure without shutting down

Back-seating isolation valves feature a secondary seating surface that seals off the packing gland when fully opened, allowing engineering watchstanders to safely repack valve stems under system pressure without securing plant operations.