Fully-Solved Practice Questions (Special Boiler)
1) A “low-pressure steam boiler” is defined (per common code usage) as a boiler that operates at
or below:
A. 30 psig
B. 15 psig
C. 100 psig
D. 160 psig
Answer: B. 15 psig
Rationale: Low-pressure steam service is ≤15 psig. (By contrast, hot-water heat is typically ≤160 psig
and ≤250°F.)
2) The maximum allowable working pressure (MAWP) stamped on a boiler nameplate is primarily
set by:
A. The safety valve rating
B. The weakest part of the pressure vessel
C. The feedwater pump discharge pressure
D. The burner size
Answer: B. The weakest part of the pressure vessel
Rationale: MAWP is governed by the limiting component of the pressure boundary (plate, drum, or
tubes), not accessories.
3) The primary purpose of a safety valve on a steam boiler is to:
A. Control normal operating pressure
B. Prevent vacuum formation
C. Release pressure to prevent the boiler from exceeding MAWP
D. Drain the boiler for maintenance
Answer: C
Rationale: Safety valves are last-line protection to keep pressure ≤ the safe limit.
4) A low-water cutoff (LWCO) should be tested:
A. Only after annual inspection
B. At regular intervals during operation (e.g., daily/shift), per SOP
C. Only when a problem occurs
D. Never, it’s automatic
Answer: B
Rationale: Routine blow-down of the LWCO float chamber (or test of probe type) ensures reliable
trip at low water.
, 5) When bringing a steam boiler online from cold, you should:
A. Fire at maximum rate to reach pressure quickly
B. Keep all drains closed to trap condensate
C. Warm up slowly with vents/drains open as directed to avoid thermal stress
D. Add chemicals after steaming starts
Answer: C
Rationale: Slow warm-up minimizes thermal shock; venting helps remove air/condensate.
6) Foaming in a boiler is most commonly caused by:
A. Low alkalinity
B. High total dissolved solids (TDS)/oils
C. Excess blowdown
D. Cold feedwater
Answer: B
Rationale: High TDS and contamination reduce surface tension, creating stable foam and carryover.
7) The first thing you do if the water level disappears from the gauge glass during firing is:
A. Open the feedwater valve wide
B. Shut down the burner immediately
C. Open the bottom blowdown
D. Increase firing rate to build pressure
Answer: B
Rationale: Possible low-water condition—secure the fire to protect the boiler. Never add water to a
potentially dry, hot boiler.
8) A mud drum blowdown is used primarily to:
A. Remove dissolved oxygen
B. Remove sludge and sediment
C. Test safety valve operation
D. Increase alkalinity
Answer: B
Rationale: Bottom blowdown clears settled solids from low points.
9) Correct combustion requires proper proportions of:
A. Fuel and water
B. Fuel and air (with adequate excess air)
C. Fuel and steam
D. Air and water
Answer: B
Rationale: Complete combustion = fuel + oxygen. A small excess air ensures full fuel burn with
minimal CO/soot.
1) A “low-pressure steam boiler” is defined (per common code usage) as a boiler that operates at
or below:
A. 30 psig
B. 15 psig
C. 100 psig
D. 160 psig
Answer: B. 15 psig
Rationale: Low-pressure steam service is ≤15 psig. (By contrast, hot-water heat is typically ≤160 psig
and ≤250°F.)
2) The maximum allowable working pressure (MAWP) stamped on a boiler nameplate is primarily
set by:
A. The safety valve rating
B. The weakest part of the pressure vessel
C. The feedwater pump discharge pressure
D. The burner size
Answer: B. The weakest part of the pressure vessel
Rationale: MAWP is governed by the limiting component of the pressure boundary (plate, drum, or
tubes), not accessories.
3) The primary purpose of a safety valve on a steam boiler is to:
A. Control normal operating pressure
B. Prevent vacuum formation
C. Release pressure to prevent the boiler from exceeding MAWP
D. Drain the boiler for maintenance
Answer: C
Rationale: Safety valves are last-line protection to keep pressure ≤ the safe limit.
4) A low-water cutoff (LWCO) should be tested:
A. Only after annual inspection
B. At regular intervals during operation (e.g., daily/shift), per SOP
C. Only when a problem occurs
D. Never, it’s automatic
Answer: B
Rationale: Routine blow-down of the LWCO float chamber (or test of probe type) ensures reliable
trip at low water.
, 5) When bringing a steam boiler online from cold, you should:
A. Fire at maximum rate to reach pressure quickly
B. Keep all drains closed to trap condensate
C. Warm up slowly with vents/drains open as directed to avoid thermal stress
D. Add chemicals after steaming starts
Answer: C
Rationale: Slow warm-up minimizes thermal shock; venting helps remove air/condensate.
6) Foaming in a boiler is most commonly caused by:
A. Low alkalinity
B. High total dissolved solids (TDS)/oils
C. Excess blowdown
D. Cold feedwater
Answer: B
Rationale: High TDS and contamination reduce surface tension, creating stable foam and carryover.
7) The first thing you do if the water level disappears from the gauge glass during firing is:
A. Open the feedwater valve wide
B. Shut down the burner immediately
C. Open the bottom blowdown
D. Increase firing rate to build pressure
Answer: B
Rationale: Possible low-water condition—secure the fire to protect the boiler. Never add water to a
potentially dry, hot boiler.
8) A mud drum blowdown is used primarily to:
A. Remove dissolved oxygen
B. Remove sludge and sediment
C. Test safety valve operation
D. Increase alkalinity
Answer: B
Rationale: Bottom blowdown clears settled solids from low points.
9) Correct combustion requires proper proportions of:
A. Fuel and water
B. Fuel and air (with adequate excess air)
C. Fuel and steam
D. Air and water
Answer: B
Rationale: Complete combustion = fuel + oxygen. A small excess air ensures full fuel burn with
minimal CO/soot.
