What is the correct sequence for air flow before lighting off the boiler?

The correct sequence for air flow before lighting off the boiler is important for ensuring safe and efficient combustion. Starting with induced air, this refers to the process where the boiler's draft system pulls air into the combustion chamber. This is essential because it establishes the necessary airflow to support combustion and helps in creating a proper draft under varying conditions.

Next is primary air, which is the air that mixes directly with the fuel for initial combustion. This air is crucial for creating a mixture that ignites cleanly and effectively. It must be carefully controlled to ensure that there is enough air to support combustion without excess, which could lead to inefficiencies or other operational issues.

Finally, secondary air enters the process. This air is used primarily to complete combustion by burning any remaining fuel particles that were not fully combusted in the initial stage. Proper introduction of secondary air is crucial for maximizing efficiency and reducing emissions.

Together, the sequence of induced, primary, and secondary air ensures that combustion occurs efficiently and safely, thus confirming the answer provided.