Question 51Steam Plants - Assistant Engineer

The correct answer is D) stop-check valve. When two or more boilers provide steam flow to a common main steam line, each boiler's main steam line must be fitted with a main steam stop valve and a stop-check valve. The stop-check valve serves as a backup to the main steam stop valve, preventing backflow from the common steam line into the individual boiler in case of a main steam stop valve failure. This redundancy is required by regulations to ensure the safe operation and isolation of the boiler system. The other options are incorrect because an auxiliary steam stop valve is not the required component, a gate valve does not provide the necessary check valve functionality, and a swing check valve, while a type of check valve, does not have the integrated stop valve feature required in this application.