Question 252Steam Plants - Assistant Engineer

The correct answer is D) manually controlled feed water regulator. In the event of a failure of the pneumatic control system, a multi-element feed water regulator is designed to operate as a manually controlled feed water regulator. This means that the feed water regulation would need to be adjusted manually by the operator, rather than automatically by the pneumatic control system. The other options, such as a constant-volume or constant-pressure regulator, would not be the appropriate design for a system that requires manual control in the case of a pneumatic failure.