American Society of Mechanical Engineers (ASME) Practice Exam

The correct choice is based on the operational procedures and safety protocols associated with boiler startups. Drum vents are typically closed once the pressure reaches 25 psig because this is the threshold that indicates the boiler is beginning to operate under its designed pressure conditions. Closing the vents at this point serves to ensure that steam produced and any potential pressure increases can be effectively contained within the system, promoting efficient operation and safety. Closing the vents too early, as indicated in the other choices, could lead to issues such as blowdowns or the inability to effectively manage residual air or non-condensables from the system. For instance, closing the vents immediately after filling the boiler might not allow for proper venting of air from the system, which is crucial during initial startup. Similarly, waiting until the system reaches steam temperature might be too late, as it can pose risks associated with over-pressurization or insufficient pressure management during the early stages of operation. Thus, closing the vent at 25 psig strikes the right balance between safety and operational efficiency.