Stationary Engineer Third Class Exam
Practice Questions And Correct Answers
(Verified Answers) Plus Rationale 2026
Q&A| Instant Download Pdf
1.A third-class stationary engineer is operating a fire-tube boiler. Which
component is primarily responsible for allowing heat from combustion gases
to transfer into the boiler water?
A. Safety valve
B. Fire tubes
C. Blowdown valve
D. Feedwater regulator
Answer: B. Fire tubes
Fire tubes carry hot combustion gases through the water-filled boiler shell,
allowing heat to transfer through the tube walls and convert water into
steam.
2. The main purpose of a boiler safety valve is to:
A. Increase steam pressure rapidly
B. Remove impurities from boiler water
C. Prevent excessive pressure buildup
D. Control fuel flow to the burner
Answer: C. Prevent excessive pressure buildup
,A safety valve automatically releases steam when pressure exceeds the set
limit, protecting the boiler from dangerous overpressure conditions.
3. In a steam boiler, the gauge glass is used to indicate:
A. Steam temperature
B. Boiler water level
C. Fuel pressure
D. Combustion efficiency
Answer: B. Boiler water level
The gauge glass provides a direct visual indication of the water level inside
the boiler, helping prevent low-water conditions.
4. Low water level in a boiler is dangerous because it can:
A. Reduce fuel consumption
B. Improve steam quality
C. Cause overheating and boiler damage
D. Increase water circulation
Answer: C. Cause overheating and boiler damage
When water level becomes too low, heating surfaces may become exposed
to intense flame temperatures, causing overheating, warping, or failure.
5. The function of a boiler feedwater pump is to:
A. Remove steam from the system
B. Supply water to the boiler
C. Increase furnace temperature
D. Remove ash from combustion chambers
Answer: B. Supply water to the boiler
A feedwater pump delivers treated water into the boiler to replace water
converted into steam and maintain proper operating levels.
, 6. The device that removes dissolved gases such as oxygen and carbon
dioxide from boiler feedwater is called a:
A. Condenser
B. Economizer
C. Deaerator
D. Superheater
Answer: C. Deaerator
A deaerator reduces corrosion by removing dissolved oxygen and carbon
dioxide from feedwater before it enters the boiler.
7. The primary purpose of boiler blowdown is to:
A. Increase boiler pressure
B. Remove concentrated impurities from water
C. Add chemicals to the boiler
D. Cool combustion gases
Answer: B. Remove concentrated impurities from water
Blowdown removes dissolved solids and sludge that accumulate in boiler
water, helping maintain proper water chemistry.
8. Boiler water treatment is necessary mainly to prevent:
A. Steam production
B. Scale and corrosion
C. Fuel ignition
D. Pressure control
Answer: B. Scale and corrosion
Proper water treatment prevents mineral deposits and chemical reactions
that reduce efficiency and damage boiler components.
9. The instrument used to measure steam pressure is a:
, A. Thermometer
B. Pressure gauge
C. Hydrometer
D. Flow meter
Answer: B. Pressure gauge
A pressure gauge measures the internal steam pressure of the boiler or
steam system and allows operators to monitor safe operation.
10. A boiler operator should always verify the operation of the low-
water cutoff because it:
A. Controls fuel quality
B. Prevents unsafe low-water firing conditions
C. Increases steam temperature
D. Measures water hardness
Answer: B. Prevents unsafe low-water firing conditions
The low-water cutoff shuts down the burner when water level falls
dangerously low, preventing overheating and possible boiler failure.
11. The process of converting water into steam inside a boiler is
called:
A. Condensation
B. Evaporation
C. Filtration
D. Expansion
Answer: B. Evaporation
Evaporation occurs when heat energy changes liquid water into steam
vapor.
12. Condensation occurs when:
Practice Questions And Correct Answers
(Verified Answers) Plus Rationale 2026
Q&A| Instant Download Pdf
1.A third-class stationary engineer is operating a fire-tube boiler. Which
component is primarily responsible for allowing heat from combustion gases
to transfer into the boiler water?
A. Safety valve
B. Fire tubes
C. Blowdown valve
D. Feedwater regulator
Answer: B. Fire tubes
Fire tubes carry hot combustion gases through the water-filled boiler shell,
allowing heat to transfer through the tube walls and convert water into
steam.
2. The main purpose of a boiler safety valve is to:
A. Increase steam pressure rapidly
B. Remove impurities from boiler water
C. Prevent excessive pressure buildup
D. Control fuel flow to the burner
Answer: C. Prevent excessive pressure buildup
,A safety valve automatically releases steam when pressure exceeds the set
limit, protecting the boiler from dangerous overpressure conditions.
3. In a steam boiler, the gauge glass is used to indicate:
A. Steam temperature
B. Boiler water level
C. Fuel pressure
D. Combustion efficiency
Answer: B. Boiler water level
The gauge glass provides a direct visual indication of the water level inside
the boiler, helping prevent low-water conditions.
4. Low water level in a boiler is dangerous because it can:
A. Reduce fuel consumption
B. Improve steam quality
C. Cause overheating and boiler damage
D. Increase water circulation
Answer: C. Cause overheating and boiler damage
When water level becomes too low, heating surfaces may become exposed
to intense flame temperatures, causing overheating, warping, or failure.
5. The function of a boiler feedwater pump is to:
A. Remove steam from the system
B. Supply water to the boiler
C. Increase furnace temperature
D. Remove ash from combustion chambers
Answer: B. Supply water to the boiler
A feedwater pump delivers treated water into the boiler to replace water
converted into steam and maintain proper operating levels.
, 6. The device that removes dissolved gases such as oxygen and carbon
dioxide from boiler feedwater is called a:
A. Condenser
B. Economizer
C. Deaerator
D. Superheater
Answer: C. Deaerator
A deaerator reduces corrosion by removing dissolved oxygen and carbon
dioxide from feedwater before it enters the boiler.
7. The primary purpose of boiler blowdown is to:
A. Increase boiler pressure
B. Remove concentrated impurities from water
C. Add chemicals to the boiler
D. Cool combustion gases
Answer: B. Remove concentrated impurities from water
Blowdown removes dissolved solids and sludge that accumulate in boiler
water, helping maintain proper water chemistry.
8. Boiler water treatment is necessary mainly to prevent:
A. Steam production
B. Scale and corrosion
C. Fuel ignition
D. Pressure control
Answer: B. Scale and corrosion
Proper water treatment prevents mineral deposits and chemical reactions
that reduce efficiency and damage boiler components.
9. The instrument used to measure steam pressure is a:
, A. Thermometer
B. Pressure gauge
C. Hydrometer
D. Flow meter
Answer: B. Pressure gauge
A pressure gauge measures the internal steam pressure of the boiler or
steam system and allows operators to monitor safe operation.
10. A boiler operator should always verify the operation of the low-
water cutoff because it:
A. Controls fuel quality
B. Prevents unsafe low-water firing conditions
C. Increases steam temperature
D. Measures water hardness
Answer: B. Prevents unsafe low-water firing conditions
The low-water cutoff shuts down the burner when water level falls
dangerously low, preventing overheating and possible boiler failure.
11. The process of converting water into steam inside a boiler is
called:
A. Condensation
B. Evaporation
C. Filtration
D. Expansion
Answer: B. Evaporation
Evaporation occurs when heat energy changes liquid water into steam
vapor.
12. Condensation occurs when:
