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 A — permit repacking the valve stem under pressure without shutting down

Refrigeration shut-off valves feature back-seats to seal the stem packing area when fully opened, permitting safe repacking of the gland under operational pressure without system evacuation or shutdown.