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DC Third Class Stationary Boilers (323) Practice
Exam Questions & Answers VERIFIED
SOLUTIONS LATEST UPDATE THIS YEAR
DC Third Class Stationary Boilers (323) Practice Exam This comprehensive practice exam is designed to help you prepare for the Washington D.C. Third Class Stationary Boilers (Exam 323) licensing examination. It covers boiler fundamentals, steam systems, fuel combustion, water treatment, safety devices, and relevant codes (ASME, OSHA). A passing score on this exam is typically 70%. Domain 1: Boiler Basics & Design Question 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 the hot combustion gases pass around them. This design allows for much higher steam pressures than fire-tube designs. Question 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).
B) 338°F
C) 500°F
D) 838°F
Answer: A Superheat is the difference between the actual steam temperature and the saturation temperature. 500°F – 338°F = 162°F of superheat. Question 5 An economizer is installed on a boiler primarily to: A) Reduce fuel consumption by pre-heating the feedwater B) Increase the pressure in the steam drum C) Lower the temperature of the flue gas D) Increase the steam output Answer: A
An economizer captures residual heat from the flue gases to preheat the feedwater entering the boiler, thereby reducing fuel consumption and improving overall efficiency. Question 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.
A) 100
B) 150
C) 500
D) 750
Answer: C One boiler horsepower (BHP) is defined as the evaporation of 34.5 pounds of water per hour from and at 212°F, which is equivalent to 10 square feet of heating surface. Therefore, 5,000 / 10 = 500 BHP. Domain 2: Boiler Operations & Safety Question 9 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. Question 10 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
Confirming the water level is the most critical safety check, as a low-water condition is the leading cause of boiler explosions. This must be done before any other operational checks. Question 12 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, preventing a catastrophic dry-fire situation.
Question 13 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. Question 14 A steam boiler is operating at 100 psi. Using the steam tables, what is the approximate corresponding saturation temperature?
Answer: B Water hammer is caused when a slug of accumulated condensate is propelled at high velocity by steam flow, impacting fittings or bends. Proper steam trapping and line drainage are essential to prevent it. Domain 3: Water Treatment & Chemistry Question 16 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. Question 17 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 Answer: B The correct sequence is: 1) Backwash (loosens the resin bed), 2) Brine (regenerates the resin with salt), 3) Rinse (flushes out excess brine and hardness), and 4) Service (normal softening operation).
B) 7.0 (neutral) C) 10.5 - 12.0 (alkaline) D) pH doesn't matter Answer: C Boiler water is maintained in an alkaline range (10.5-12.0) to prevent acid-based corrosion. This alkalinity also helps precipitate hardness minerals so they can be removed by blowdown. Question 20 What is caustic embrittlement? A) A type of boiler fuel B) Cracking of boiler metal due to concentrated caustic solutions C) A water treatment chemical D) A type of scale Answer: B
Caustic embrittlement is a form of stress corrosion cracking that occurs when caustic (alkaline) boiler water becomes concentrated in crevices or under deposits, leading to cracking of the boiler metal. Question 21 What is the purpose of a blowdown valve? A) To add water to the boiler B) To remove sediment and concentrated impurities from the boiler C) To release steam D) To test safety valves Answer: B Blowdown valves are used to remove concentrated impurities and sludge that settle at the bottom of the boiler (bottom blowdown) or to remove dissolved solids from the surface (continuous blowdown).
A) Yellow B) Red C) Blue D) Orange Answer: C A properly adjusted natural gas flame should be blue with a distinct inner cone. This indicates complete combustion with the correct air-fuel ratio. Question 24 What indicates incomplete combustion? A) Clear stack discharge B) Black smoke or high CO levels C) High oxygen in flue gas D) Low fuel consumption
Answer: B Incomplete combustion is indicated by black smoke (soot) or high levels of carbon monoxide (CO) in the flue gas. Both are signs of insufficient air for complete burning. Question 25 What is excess air in combustion? A) Air that escapes from the boiler room B) Air supplied beyond what's theoretically needed for complete combustion C) Air that causes incomplete combustion D) Atmospheric air pressure Answer: B Excess air is the amount of air supplied to the burner beyond the stoichiometric (theoretical) requirement. Some excess air is necessary for safety and complete combustion, but too much reduces efficiency by carrying heat out the stack.
