According to heating boiler code, where should an additional stop valve be placed when one is used in the supply pipe connection of a single steam boiler?

The placement of an additional stop valve in the supply pipe connection of a single steam boiler is important for ensuring proper operation and safety. The correct answer indicates that the stop valve should be located in the return pipe connection. This positioning allows for easy isolation of the boiler for maintenance or inspection without affecting the entire system.

By placing the stop valve in the return line, technicians can safely drain the boiler or perform necessary repairs while ensuring that the flow of steam or water continues in the supply line. This minimizes downtime and maintains system efficiency.

In contrast, placing the valve directly in the supply pipe could create difficulties when the boiler needs service, as it may require shutting down the entire system. Other options, such as before or after the boiler, may also disrupt the overall function or lead to unnecessary complications when managing system pressures and controls. Thus, the correct placement in the return pipe connection aligns with best practices for boiler operation and maintenance.