Boiler Operation, Startup, and Shutdown Procedures
Core concepts
Startup and shutdown follow a disciplined sequence designed to protect the pressure vessel from thermal stress and to keep water level safe. Before lighting off, verify: water level at the normal operating level in the gauge glass, all vents and drains in correct position, feedwater available, fuel supply proven, draft established, and all interlocks and trips in service. Warm the boiler slowly; a common rule is to raise pressure slowly and to warm a cold boiler over several hours, because rapid heating causes uneven expansion and stress.
During startup, open the air vent or superheater drain until steam appears, then close it; warm the steam line by slowly opening the main stop (or bypass) and draining the line. During normal operation, maintain level at the center of the gauge glass, watch the flame and stack, and log pressure, temperature, and water level. During shutdown, reduce firing gradually, blow down as required while pressure remains, secure the fuel, and allow the boiler to cool naturally; do not dump pressure rapidly or refill a hot boiler with cold water.
Traps
Questions test the order of steps: vents open before light-off, closed when steam appears; the feedwater check valve orientation; whether the low-water cutoff can be bypassed (never during firing); and the correct action when the gauge glass is empty (secure the fuel first, not add water blindly).
Worked example
Rule of thumb: if the water level is lost, shut off fuel immediately and do not add water until the boiler has cooled and the cause is found, because adding water to a hot, dry boiler can cause a violent collapse of steam.