Understanding the entire gas train operating sequence helps to correctly interpret every valve, pressure switch and interlock.
Standby
The main gas valves are closed and the system awaits a start command.
Valve proving
Where present, the tightness of V1 and V2 is checked before ignition is permitted.
Permissives
Gas pressure, combustion air, valve position, and all essential interlocks are verified.
Ignition
A controlled amount of start gas is provided and ignition is activated. The flame must be confirmed within the safety time.
Main flame
After flame confirmation, the gas train allows transition to normal supply and modulation.
Shutdown
During normal shutdown or a trip, the gas valves close and the system returns to a safe state.
