DC Third Class Stationary Boilers (323)
Exam Questions And Answers Rated A+
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1. Which type of boiler contains water inside the tubes with hot combustion gases
passing outside?
A) Fire-tube boiler
B) Water-tube boiler
C) Cast iron sectional boiler
D) Electric boiler
Answer: B
In a water-tube boiler, water circulates inside the tubes while hot combustion gases pass
around the outside. This design allows for much higher steam pressures and capacities
than fire-tube designs, making them suitable for large industrial applications .
2. What is the primary function of a safety valve on a boiler?
A) To regulate the boiler's operating pressure
B) To automatically release steam to prevent over-pressurization
C) To remove dissolved solids from the boiler water
D) To vent air during the startup process
Answer: B
A safety valve is a spring-loaded device designed to automatically open at a set pressure
to prevent the boiler from exceeding its Maximum Allowable Working Pressure (MAWP).
This is a critical safety device that prevents catastrophic explosions .
,3. According to the ASME Code, a high-pressure boiler with more than 500 square
feet of heating surface must have:
A) One safety valve on the steam drum
B) Two or more safety valves
C) An automatic non-return valve
D) A pressure relief valve on the superheater only
Answer: B
The ASME Boiler and Pressure Vessel Code mandates that boilers exceeding 500 square
feet of heating surface must have two or more safety valves to ensure adequate
relieving capacity in case one valve fails or is insufficient .
4. What is the purpose of a low water cutoff device?
A) A valve that stops water flow
B) A safety device that shuts down the burner when water level is too low
C) A device to measure water hardness
D) A manual shutoff valve
Answer: B
A low water cutoff (LWCO) is a safety device that automatically shuts off the burner if
the water level drops below a safe point. This prevents a dry-fire condition which can
lead to catastrophic tube failure and boiler explosions .
5. What is the purpose of a pressure gauge siphon?
A) To create pressure
B) To protect the gauge from direct steam contact and high temperature
C) To drain water
D) To increase pressure readings
Answer: B
A pressure gauge siphon (pigtail) traps a small amount of water between the steam line
and the gauge. This water protects the sensitive gauge mechanism from the damaging
effects of high-temperature steam, ensuring accurate readings .
,6. What is the normal operating water level in a boiler gauge glass?
A) At the top
B) At the bottom
C) At the middle or as per manufacturer's specifications
D) Water level doesn't matter
Answer: C
The normal water level is typically maintained at the middle of the gauge glass. This
ensures adequate water coverage of the heating surfaces and provides a buffer for
fluctuations, preventing both low-water and carryover conditions .
7. A boiler operator notices the water level is dropping rapidly. What is the most
immediate and safest action?
A) Increase the fuel supply to compensate for the water loss
B) Shut the boiler down immediately to prevent a catastrophic tube failure
C) Open the feedwater valve wider to flood the boiler
D) Increase the steam demand to balance the level
Answer: B
A rapid drop in water level indicates a low-water condition, which can lead to
overheating of tubes and a catastrophic boiler explosion. Immediate shutdown is
required to protect the equipment and personnel before investigating the cause .
8. A gauge glass is blown down primarily to:
A) Lower the water level before lighting off the boiler
B) Verify that the water column connections are clear and the gauge is showing an
accurate level
C) Clean the outside of the glass
D) Reduce the water level to prevent carryover
Answer: B
Blowing down the gauge glass verifies that the water column connections to the boiler
, are clear of sludge and sediment. This ensures the gauge glass is indicating an accurate
water level, which is essential for safe boiler operation .
9. What is water hammer in a steam system?
A) A tool used to test boiler tubes
B) A loud banging noise caused by condensate being carried with high-velocity steam
C) A type of pump used for feedwater
D) A device for measuring water pressure
Answer: B
Water hammer is caused when a slug of accumulated condensate is propelled at high
velocity by steam flow, impacting fittings or bends. This can cause significant damage to
piping and equipment. Proper steam trapping and line drainage are essential to prevent
it .
10. What is the purpose of boiler water treatment?
A) To increase fuel efficiency only
B) To prevent scale, corrosion, and carryover
C) To increase water temperature
D) To reduce steam production
Answer: B
The primary purpose of water treatment is to prevent the formation of scale (which
insulates heating surfaces), corrosion (which damages metal), and carryover (which
contaminates steam) by controlling chemical properties and removing impurities from
the feedwater .
11. The proper sequence for a zeolite water softener regeneration cycle is:
A) Service → Backwash → Rinse → Brine
B) Backwash → Brine → Rinse → Service
C) Brine → Rinse → Backwash → Service
D) Rinse → Service → Backwash → Brine
Exam Questions And Answers Rated A+
New Update Assured Satisfaction
1. Which type of boiler contains water inside the tubes with hot combustion gases
passing outside?
A) Fire-tube boiler
B) Water-tube boiler
C) Cast iron sectional boiler
D) Electric boiler
Answer: B
In a water-tube boiler, water circulates inside the tubes while hot combustion gases pass
around the outside. This design allows for much higher steam pressures and capacities
than fire-tube designs, making them suitable for large industrial applications .
2. What is the primary function of a safety valve on a boiler?
A) To regulate the boiler's operating pressure
B) To automatically release steam to prevent over-pressurization
C) To remove dissolved solids from the boiler water
D) To vent air during the startup process
Answer: B
A safety valve is a spring-loaded device designed to automatically open at a set pressure
to prevent the boiler from exceeding its Maximum Allowable Working Pressure (MAWP).
This is a critical safety device that prevents catastrophic explosions .
,3. According to the ASME Code, a high-pressure boiler with more than 500 square
feet of heating surface must have:
A) One safety valve on the steam drum
B) Two or more safety valves
C) An automatic non-return valve
D) A pressure relief valve on the superheater only
Answer: B
The ASME Boiler and Pressure Vessel Code mandates that boilers exceeding 500 square
feet of heating surface must have two or more safety valves to ensure adequate
relieving capacity in case one valve fails or is insufficient .
4. What is the purpose of a low water cutoff device?
A) A valve that stops water flow
B) A safety device that shuts down the burner when water level is too low
C) A device to measure water hardness
D) A manual shutoff valve
Answer: B
A low water cutoff (LWCO) is a safety device that automatically shuts off the burner if
the water level drops below a safe point. This prevents a dry-fire condition which can
lead to catastrophic tube failure and boiler explosions .
5. What is the purpose of a pressure gauge siphon?
A) To create pressure
B) To protect the gauge from direct steam contact and high temperature
C) To drain water
D) To increase pressure readings
Answer: B
A pressure gauge siphon (pigtail) traps a small amount of water between the steam line
and the gauge. This water protects the sensitive gauge mechanism from the damaging
effects of high-temperature steam, ensuring accurate readings .
,6. What is the normal operating water level in a boiler gauge glass?
A) At the top
B) At the bottom
C) At the middle or as per manufacturer's specifications
D) Water level doesn't matter
Answer: C
The normal water level is typically maintained at the middle of the gauge glass. This
ensures adequate water coverage of the heating surfaces and provides a buffer for
fluctuations, preventing both low-water and carryover conditions .
7. A boiler operator notices the water level is dropping rapidly. What is the most
immediate and safest action?
A) Increase the fuel supply to compensate for the water loss
B) Shut the boiler down immediately to prevent a catastrophic tube failure
C) Open the feedwater valve wider to flood the boiler
D) Increase the steam demand to balance the level
Answer: B
A rapid drop in water level indicates a low-water condition, which can lead to
overheating of tubes and a catastrophic boiler explosion. Immediate shutdown is
required to protect the equipment and personnel before investigating the cause .
8. A gauge glass is blown down primarily to:
A) Lower the water level before lighting off the boiler
B) Verify that the water column connections are clear and the gauge is showing an
accurate level
C) Clean the outside of the glass
D) Reduce the water level to prevent carryover
Answer: B
Blowing down the gauge glass verifies that the water column connections to the boiler
, are clear of sludge and sediment. This ensures the gauge glass is indicating an accurate
water level, which is essential for safe boiler operation .
9. What is water hammer in a steam system?
A) A tool used to test boiler tubes
B) A loud banging noise caused by condensate being carried with high-velocity steam
C) A type of pump used for feedwater
D) A device for measuring water pressure
Answer: B
Water hammer is caused when a slug of accumulated condensate is propelled at high
velocity by steam flow, impacting fittings or bends. This can cause significant damage to
piping and equipment. Proper steam trapping and line drainage are essential to prevent
it .
10. What is the purpose of boiler water treatment?
A) To increase fuel efficiency only
B) To prevent scale, corrosion, and carryover
C) To increase water temperature
D) To reduce steam production
Answer: B
The primary purpose of water treatment is to prevent the formation of scale (which
insulates heating surfaces), corrosion (which damages metal), and carryover (which
contaminates steam) by controlling chemical properties and removing impurities from
the feedwater .
11. The proper sequence for a zeolite water softener regeneration cycle is:
A) Service → Backwash → Rinse → Brine
B) Backwash → Brine → Rinse → Service
C) Brine → Rinse → Backwash → Service
D) Rinse → Service → Backwash → Brine
