What is a through stay designed to do?

A through stay is designed to connect two separate boiler sections, providing structural integrity and stability. In boiler systems, multiple sections may be used to increase efficiency or capacity, and the through stay serves to securely link these sections together. This connection is essential for maintaining the alignment of the boiler components under varying pressures and temperatures, ensuring proper operation and safety. By providing a robust connection, through stays help to distribute stresses that occur during operation, preventing potential failure or misalignment of the boiler.

The other answer choices relate to different functions that are not applicable to a through stay. Supporting a sliding door pertains to a mechanical aspect unrelated to boiler structure, while regulating steam pressure and controlling combustion airflow refer to operational processes within the boiler rather than the physical connection between its sections.