Stationary Engineer First Class Exam
Practice Questions And Correct Answers
(Verified Answers) Plus Rationale 2026
Q&A| Instant Download Pdf
1. A high-pressure water-tube boiler operating at full load begins to show
a gradual decrease in steam pressure while the firing rate remains
constant. Which condition is the most likely cause?
A. Increased feedwater temperature
B. Excessive boiler blowdown
C. Reduced steam demand
D. Increased deaerator pressure
Answer: B. Excessive boiler blowdown
Rationale: Excessive blowdown removes heated water from the boiler faster
than necessary, reducing the available energy for steam generation and
causing steam pressure to decrease even though firing rate remains
unchanged.
2. Which boiler safety device is intended to automatically shut off the
fuel supply if the water level falls below a safe operating point?
A. Pressure gauge
B. Feedwater regulator
,C. Low-water fuel cutoff
D. Steam separator
Answer: C. Low-water fuel cutoff
Rationale: The low-water fuel cutoff protects the boiler from overheating
and catastrophic failure by stopping fuel flow whenever the water level
becomes dangerously low.
3. During a routine inspection, a Stationary Engineer observes that the
safety valve has been leaking slightly under normal operating pressure.
What should be done first?
A. Tighten the adjustment screw
B. Plug the valve temporarily
C. Report the condition and remove the boiler from service if necessary
D. Increase boiler pressure to reseat the valve
Answer: C. Report the condition and remove the boiler from service if
necessary
Rationale: Safety valves are critical pressure-relief devices. Leakage may
indicate improper seating or malfunction and requires evaluation according
to operating procedures without unauthorized adjustment.
4. The primary purpose of a deaerator in a boiler plant is to:
A. Increase steam pressure
B. Remove dissolved oxygen and carbon dioxide from feedwater
C. Cool condensate before pumping
D. Reduce boiler blowdown frequency
Answer: B. Remove dissolved oxygen and carbon dioxide from feedwater
,Rationale: Dissolved gases promote corrosion within boilers and piping
systems. A deaerator removes these gases to extend equipment life and
improve system reliability.
5. A centrifugal pump is cavitating. Which condition is the most likely
cause?
A. Excessive discharge pressure
B. Insufficient net positive suction head
C. High motor efficiency
D. Excessive lubrication
Answer: B. Insufficient net positive suction head
Rationale: Cavitation occurs when pressure at the pump suction falls below
the liquid's vapor pressure, causing vapor bubbles that collapse inside the
pump and damage internal components.
6. Which combustion condition generally produces the highest
concentration of carbon monoxide?
A. Excess excess air
B. Perfect combustion
C. Insufficient combustion air
D. High stack temperature
Answer: C. Insufficient combustion air
Rationale: Carbon monoxide forms when there is inadequate oxygen to
completely oxidize carbon into carbon dioxide during combustion.
7. What is the primary purpose of boiler blowdown?
A. Increase boiler pressure
B. Remove accumulated dissolved and suspended solids
, C. Raise feedwater temperature
D. Improve burner efficiency
Answer: B. Remove accumulated dissolved and suspended solids
Rationale: Blowdown controls the concentration of impurities that would
otherwise cause scale formation, foaming, and corrosion within the boiler.
8. Which instrument provides the operator with a direct indication of
boiler water level?
A. Thermocouple
B. Gauge glass
C. Bourdon pressure gauge
D. Flow transmitter
Answer: B. Gauge glass
Rationale: The gauge glass provides a visual indication of the actual water
level inside the boiler drum, allowing continuous monitoring by the operator.
9. Which law explains why increasing the pressure of a confined gas
generally increases its temperature if no heat is removed?
A. Ohm's Law
B. Boyle's Law
C. Charles's Law
D. Combined Gas Law
Answer: D. Combined Gas Law
Rationale: The Combined Gas Law describes the relationship among
pressure, volume, and temperature for a fixed amount of gas, explaining
temperature increases during compression.
10. When locking out electrical equipment before maintenance, the
first objective is to:
Practice Questions And Correct Answers
(Verified Answers) Plus Rationale 2026
Q&A| Instant Download Pdf
1. A high-pressure water-tube boiler operating at full load begins to show
a gradual decrease in steam pressure while the firing rate remains
constant. Which condition is the most likely cause?
A. Increased feedwater temperature
B. Excessive boiler blowdown
C. Reduced steam demand
D. Increased deaerator pressure
Answer: B. Excessive boiler blowdown
Rationale: Excessive blowdown removes heated water from the boiler faster
than necessary, reducing the available energy for steam generation and
causing steam pressure to decrease even though firing rate remains
unchanged.
2. Which boiler safety device is intended to automatically shut off the
fuel supply if the water level falls below a safe operating point?
A. Pressure gauge
B. Feedwater regulator
,C. Low-water fuel cutoff
D. Steam separator
Answer: C. Low-water fuel cutoff
Rationale: The low-water fuel cutoff protects the boiler from overheating
and catastrophic failure by stopping fuel flow whenever the water level
becomes dangerously low.
3. During a routine inspection, a Stationary Engineer observes that the
safety valve has been leaking slightly under normal operating pressure.
What should be done first?
A. Tighten the adjustment screw
B. Plug the valve temporarily
C. Report the condition and remove the boiler from service if necessary
D. Increase boiler pressure to reseat the valve
Answer: C. Report the condition and remove the boiler from service if
necessary
Rationale: Safety valves are critical pressure-relief devices. Leakage may
indicate improper seating or malfunction and requires evaluation according
to operating procedures without unauthorized adjustment.
4. The primary purpose of a deaerator in a boiler plant is to:
A. Increase steam pressure
B. Remove dissolved oxygen and carbon dioxide from feedwater
C. Cool condensate before pumping
D. Reduce boiler blowdown frequency
Answer: B. Remove dissolved oxygen and carbon dioxide from feedwater
,Rationale: Dissolved gases promote corrosion within boilers and piping
systems. A deaerator removes these gases to extend equipment life and
improve system reliability.
5. A centrifugal pump is cavitating. Which condition is the most likely
cause?
A. Excessive discharge pressure
B. Insufficient net positive suction head
C. High motor efficiency
D. Excessive lubrication
Answer: B. Insufficient net positive suction head
Rationale: Cavitation occurs when pressure at the pump suction falls below
the liquid's vapor pressure, causing vapor bubbles that collapse inside the
pump and damage internal components.
6. Which combustion condition generally produces the highest
concentration of carbon monoxide?
A. Excess excess air
B. Perfect combustion
C. Insufficient combustion air
D. High stack temperature
Answer: C. Insufficient combustion air
Rationale: Carbon monoxide forms when there is inadequate oxygen to
completely oxidize carbon into carbon dioxide during combustion.
7. What is the primary purpose of boiler blowdown?
A. Increase boiler pressure
B. Remove accumulated dissolved and suspended solids
, C. Raise feedwater temperature
D. Improve burner efficiency
Answer: B. Remove accumulated dissolved and suspended solids
Rationale: Blowdown controls the concentration of impurities that would
otherwise cause scale formation, foaming, and corrosion within the boiler.
8. Which instrument provides the operator with a direct indication of
boiler water level?
A. Thermocouple
B. Gauge glass
C. Bourdon pressure gauge
D. Flow transmitter
Answer: B. Gauge glass
Rationale: The gauge glass provides a visual indication of the actual water
level inside the boiler drum, allowing continuous monitoring by the operator.
9. Which law explains why increasing the pressure of a confined gas
generally increases its temperature if no heat is removed?
A. Ohm's Law
B. Boyle's Law
C. Charles's Law
D. Combined Gas Law
Answer: D. Combined Gas Law
Rationale: The Combined Gas Law describes the relationship among
pressure, volume, and temperature for a fixed amount of gas, explaining
temperature increases during compression.
10. When locking out electrical equipment before maintenance, the
first objective is to:
