An ASME code stamp is needed for what part of a boiler installation?

In the context of a boiler installation, an ASME (American Society of Mechanical Engineers) code stamp is required on pressure-retaining parts that are crucial for safety and operation. The first stop valve is vital as it controls the flow of steam or water in and out of the boiler, and it is typically subject to high pressure.

The ASME code stipulates that safety components, which include certain valves in a boiler system, must adhere to rigorous standards ensuring they can safely handle the pressures and temperatures expected in service. This is critical because a failure in the first stop valve could lead to catastrophic failure of the boiler system.

The other options, while important components of a boiler system, do not require the same level of scrutiny under ASME codes as the first stop valve does. The main pump, expansion tank, and safety valve have their own standards and requirements, but the first stop valve specifically is one of the components most closely regulated to ensure the safe operation of the boiler under ASME guidelines.