Question 255Steam Plants - 1st Asst/Chief

The correct answer is D) Clogged air ejector nozzle steam strainers. The air ejector is responsible for maintaining vacuum in the main condenser by removing air and other non-condensable gases. If the air ejector nozzle steam strainers become clogged, it can restrict the flow of steam to the ejector, making it harder to maintain the necessary vacuum. When switching to the standby unit, the vacuum returns to normal, indicating the issue is likely with the primary air ejector system. The other options are incorrect because excessive cooling water (A) and excessive feed water pump speed (C) would not cause the vacuum issues specifically in the main condenser. An open drain line from the after condenser (B) may affect the vacuum, but the prompt states the issue is noticed when switching to the standby unit, suggesting the problem is with the primary air ejector system.