Question 260General Subjects - Assistant Engineer

The correct answer is D. The control valve has two discs which are both downward seating. The reason this is correct is that in a pneumatically operated diaphragm actuated control valve, the valve discs are designed to be downward seating. This configuration allows the valve to fail in the closed position when the pneumatic supply is lost, which is a common safety feature for this type of valve. The two discs ensure a tight seal when the valve is closed. The other options are incorrect because a single disc valve would not provide the redundancy and fail-safe behavior required for this type of critical control valve. Additionally, upward seating valves are less common in this application and would not provide the desired fail-closed functionality.