An industrial burner does not start simply because there is an ON command. The Burner Management System (BMS) or equivalent automation checks a series of permissives and interlocks before allowing gas supply and ignition.
What are permissives
Permissives are the conditions that must be correct for the sequence to start. Examples include sufficient gas pressure, available combustion air, correct valve position, absence of active trips, and fan readiness.
Pre-purge
Before ignition, the combustion chamber is purged for a specific time and airflow. The BMS must confirm the required conditions before proceeding to the next step.
Valve checking
Depending on the system, it is confirmed that the gas valves are in the required position and that the leak test has been completed successfully. Failure of valve proving must stop the sequence.
Gas pressure
Low and high gas pressure switches monitor that the pressure is within the permissible range. If a contact is not in the correct state, the burner should not be granted start permission.
Ignition and flame monitoring
After the ignition command, the system waits for flame confirmation within the allowed safety time. If no flame is detected, the gas valves close and the system is led to a safe state.
Why sequence diagnosis is needed
In the event of a fault, it is more effective to identify the step at which the sequence stopped rather than replacing components at random. The BMS screen, status bits, and alarm history are essential diagnostic tools.
