Boiler Operation, Starting Up and Shutting Down
Starting up
Understand the sequence: confirm the boiler is filled to the correct level, check all mountings, prove gauge glasses, ensure vents and drains are open, purge the furnace, then light the burner or fire. Warm through slowly to avoid thermal stress. Raise pressure gradually, blow down gauge glasses, test safety valves and low-water alarms, and only then bring the boiler on line. Know why air vents are left open until steam appears and why warming through is essential.
Normal operation
Know the routine checks: water level, steam pressure, feedwater quality, burner flame, draught, stack temperature and blowdown schedule. Understand bottom blowdown and surface blowdown and their different purposes. Know how to change from manual to automatic control safely and how to respond to fluctuating load.
Shutting down
Distinguish normal shutdown from emergency shutdown. For a normal shutdown, reduce firing, allow cooling, blow down as required, and isolate. For an emergency, cut fuel first, then isolate. Understand why a hot boiler must not be cooled rapidly or drained while hot, and why air must not be admitted to a hot boiler.
Traps
Questions often test the order of actions. Purging before lighting is critical; failure to purge can cause a furnace explosion. Another trap is draining a hot boiler, which can cause thermal shock and damage. Do not confuse the vent with the safety valve; the vent must be open during warm-up.
Worked example
If asked what to do first on a low-water condition, reason: if the level is not visible, cut fuel and do not admit feedwater until the boiler is cool, because adding water to a hot, overheated shell can cause sudden violent evaporation.
Rule of thumb
Fuel first in an emergency; purge first before lighting; warm through slowly and cool slowly.