Dc Third Class Stationary Boilers (323)
Exam Questions and Correct Answers With
Rationales
1. What is the primary purpose of a boiler’s fusible plug?
a) Reduce pressure in the boiler
b) Indicate water level
c) Prevent overheating by melting if water level is too low
d) Control fuel flow
The fusible plug melts at high temperatures, alerting operators to
low water conditions and preventing boiler damage.
2. The most common method of heat transfer in a water-tube boiler
is:
a) Conduction
b) Convection
c) Radiation
d) Induction
Water-tube boilers primarily rely on convective heat transfer as
water moves through the tubes and absorbs heat from hot gases.
3. Which type of boiler is best suited for high-pressure steam
applications?
a) Fire-tube boiler
b) Water-tube boiler
, c) Electric boiler
d) Waste-heat boiler
Water-tube boilers can withstand higher pressures and
temperatures due to their design.
4. What is the purpose of the boiler blowdown?
a) To add water to the system
b) To remove dissolved solids and prevent scale
c) To vent steam to the atmosphere
d) To circulate fuel
Blowdown removes sediments and dissolved minerals,
maintaining efficiency and preventing scale formation.
5. Which device prevents the backflow of water into the boiler feed
line?
a) Pressure relief valve
b) Fusible plug
c) Check valve
d) Safety valve
Check valves allow flow in only one direction, preventing backflow
into the feed system.
6. What is the function of the superheater in a boiler?
a) Reduce pressure
b) Increase steam temperature above saturation
c) Store water
d) Filter impurities
Superheaters heat saturated steam, producing dry steam for high-
efficiency power applications.
, 7. Which type of fuel causes the most slagging and fouling in boilers?
a) Natural gas
b) Coal
c) Diesel
d) Propane
Coal contains ash and other minerals that contribute to slagging
and fouling in boiler tubes.
8. What is the main purpose of a boiler economizer?
a) Increase steam pressure
b) Recover heat from flue gases
c) Remove moisture from steam
d) Control water level
Economizers capture residual heat from flue gases to preheat
boiler feedwater, improving efficiency.
9. In a fire-tube boiler, where does the combustion take place?
a) Inside the tubes surrounded by water
b) Outside the tubes
c) In the superheater
d) In the economizer
Fire-tube boilers have hot gases passing through tubes, with water
surrounding them to absorb heat.
10. Which of the following indicates low water in a boiler?
a) Pressure gauge
b) Flow meter
c) Water-level gauge
d) Thermocouple
Exam Questions and Correct Answers With
Rationales
1. What is the primary purpose of a boiler’s fusible plug?
a) Reduce pressure in the boiler
b) Indicate water level
c) Prevent overheating by melting if water level is too low
d) Control fuel flow
The fusible plug melts at high temperatures, alerting operators to
low water conditions and preventing boiler damage.
2. The most common method of heat transfer in a water-tube boiler
is:
a) Conduction
b) Convection
c) Radiation
d) Induction
Water-tube boilers primarily rely on convective heat transfer as
water moves through the tubes and absorbs heat from hot gases.
3. Which type of boiler is best suited for high-pressure steam
applications?
a) Fire-tube boiler
b) Water-tube boiler
, c) Electric boiler
d) Waste-heat boiler
Water-tube boilers can withstand higher pressures and
temperatures due to their design.
4. What is the purpose of the boiler blowdown?
a) To add water to the system
b) To remove dissolved solids and prevent scale
c) To vent steam to the atmosphere
d) To circulate fuel
Blowdown removes sediments and dissolved minerals,
maintaining efficiency and preventing scale formation.
5. Which device prevents the backflow of water into the boiler feed
line?
a) Pressure relief valve
b) Fusible plug
c) Check valve
d) Safety valve
Check valves allow flow in only one direction, preventing backflow
into the feed system.
6. What is the function of the superheater in a boiler?
a) Reduce pressure
b) Increase steam temperature above saturation
c) Store water
d) Filter impurities
Superheaters heat saturated steam, producing dry steam for high-
efficiency power applications.
, 7. Which type of fuel causes the most slagging and fouling in boilers?
a) Natural gas
b) Coal
c) Diesel
d) Propane
Coal contains ash and other minerals that contribute to slagging
and fouling in boiler tubes.
8. What is the main purpose of a boiler economizer?
a) Increase steam pressure
b) Recover heat from flue gases
c) Remove moisture from steam
d) Control water level
Economizers capture residual heat from flue gases to preheat
boiler feedwater, improving efficiency.
9. In a fire-tube boiler, where does the combustion take place?
a) Inside the tubes surrounded by water
b) Outside the tubes
c) In the superheater
d) In the economizer
Fire-tube boilers have hot gases passing through tubes, with water
surrounding them to absorb heat.
10. Which of the following indicates low water in a boiler?
a) Pressure gauge
b) Flow meter
c) Water-level gauge
d) Thermocouple
