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NYC Custodian Engineer Exam: 100 Practice Questions with Answers and Rationales
Section 1: Boiler Operations & Steam Systems (Questions 1-25)
1. According to the NYC Mechanical Code, what is the maximum allowable pressure for a
boiler to be classified as a "low-pressure" steam boiler?
A. 5 psi
B. 15 psi
C. 100 psi
D. 150 psi
Answer: B
Low-pressure steam boilers are limited to 15 psig. Any boiler operating above this pressure is
classified as high-pressure and requires a different class of licensure .
2. What is the primary function of the Hartford Loop in a steam heating system?
A. To increase steam velocity
B. To prevent the boiler from losing water level if the return line leaks
C. To circulate hot water
D. To regulate steam temperature
Answer: B
The Hartford Loop is a safety piping arrangement that maintains water level in the boiler
even if the return line leaks or breaks, protecting the crown sheet from overheating .
3. If a Custodian Engineer observes "priming" or "foaming" in the boiler sight glass, what is
the most likely cause?
A. Low water level
B. High concentration of dissolved solids or oil in the water
C. Excessive oxygen
D. Scale buildup
Answer: B
Foaming is caused by impurities on the water surface. A surface blowdown removes these
impurities to prevent water carryover into steam lines .
4. Which device is mandated by NYC code to shut off fuel supply if water level drops below
the lowest safe operating point?
A. Pressuretrol
B. Aqua-stat
C. Low-water cutoff
D. OS&Y valve
Answer: C
The low-water cutoff is the most critical safety device, preventing a dry-fire condition that
could lead to a catastrophic boiler explosion .
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5. In a fire-tube boiler:
A. Water passes through tubes surrounded by combustion gases
B. Combustion gases pass through tubes surrounded by water
C. Both water and gases flow through the same tubes
D. There are no tubes
Answer: B
Fire-tube boilers have hot combustion gases passing through tubes surrounded by water .
6. The expansion tank in a hot water heating system is designed to:
A. Allow for expansion of water as it heats
B. Increase water pressure
C. Store hot water for later use
D. Reduce water temperature
Answer: A
As water heats, it expands. The expansion tank provides space for expanded water to
prevent pressure buildup .
7. What is the purpose of a safety valve on a steam boiler?
A. To regulate steam pressure during normal operation
B. To release pressure if it exceeds the maximum allowable working pressure
C. To add water to the boiler
D. To measure steam temperature
Answer: B
Safety valves are the final protection against overpressure and must be tested regularly .
8. What is "scale" in a boiler, and why is it dangerous?
A. Hard mineral deposits that act as an insulator, causing tubes to overheat
B. The weight of the boiler when empty
C. A layer of oil on top of the water
D. Rust on the outside of the boiler shell
Answer: A
Scale prevents water from cooling the tubes, allowing the fire to melt or weaken the steel .
9. What is "pitting" in a boiler's metal surfaces?
A. Small, deep holes caused by localized oxygen corrosion
B. Large dents caused by a hammer
C. Surface discoloration
D. Weld marks
Answer: A
Pitting is localized corrosion that creates small, deep holes in metal .
10. What is "primary air" in a burner?
A. Air mixed with fuel before it reaches the point of ignition
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B. Air used to cool the boiler room
C. Air sucked up the chimney
D. Air coming through windows
Answer: A
Primary air starts combustion; secondary air is added later to complete the burn .
11. What does a steam pressure gauge measure?
A. Pressure inside the boiler in PSI above atmospheric pressure
B. Temperature of steam
C. Weight of steam in pipes
D. Volume of steam being used
Answer: A
Standard gauges show gauge pressure (psig); to get absolute pressure (psia), add 14.7 psi .
12. What is the function of a siphon (pigtail) in a steam pressure gauge installation?
A. To suck water into the gauge
B. To create a water seal that protects internal gauge parts from steam
C. To increase pressure reading
D. To drain the boiler
Answer: B
The siphon creates a water seal that protects the gauge from the high temperature of steam
.
13. When a low-pressure boiler is short-cycling repeatedly during peak heating hours,
what is the MOST appropriate first action?
A. Immediately shut down the boiler
B. Check the boiler's operating control settings and differential
C. Increase the boiler's firing rate
D. Bleed all radiators
Answer: B
Short-cycling is often caused by improper control settings. Verify and adjust settings before
escalating .
14. A Custodian Engineer notices a faint odor of natural gas in the boiler room. What is the
FIRST course of action?
A. Locate the main gas shut-off valve and close it
B. Ventilate by opening windows
C. Evacuate the area and call 911 from a remote location
D. Ignite a lighter to test for the leak
Answer: C
Any action that could create a spark poses ignition risk. Evacuation and calling from a safe
remote location is the mandated first step .
NYC Custodian Engineer Exam: 100 Practice Questions with Answers and Rationales
Section 1: Boiler Operations & Steam Systems (Questions 1-25)
1. According to the NYC Mechanical Code, what is the maximum allowable pressure for a
boiler to be classified as a "low-pressure" steam boiler?
A. 5 psi
B. 15 psi
C. 100 psi
D. 150 psi
Answer: B
Low-pressure steam boilers are limited to 15 psig. Any boiler operating above this pressure is
classified as high-pressure and requires a different class of licensure .
2. What is the primary function of the Hartford Loop in a steam heating system?
A. To increase steam velocity
B. To prevent the boiler from losing water level if the return line leaks
C. To circulate hot water
D. To regulate steam temperature
Answer: B
The Hartford Loop is a safety piping arrangement that maintains water level in the boiler
even if the return line leaks or breaks, protecting the crown sheet from overheating .
3. If a Custodian Engineer observes "priming" or "foaming" in the boiler sight glass, what is
the most likely cause?
A. Low water level
B. High concentration of dissolved solids or oil in the water
C. Excessive oxygen
D. Scale buildup
Answer: B
Foaming is caused by impurities on the water surface. A surface blowdown removes these
impurities to prevent water carryover into steam lines .
4. Which device is mandated by NYC code to shut off fuel supply if water level drops below
the lowest safe operating point?
A. Pressuretrol
B. Aqua-stat
C. Low-water cutoff
D. OS&Y valve
Answer: C
The low-water cutoff is the most critical safety device, preventing a dry-fire condition that
could lead to a catastrophic boiler explosion .
, 2
5. In a fire-tube boiler:
A. Water passes through tubes surrounded by combustion gases
B. Combustion gases pass through tubes surrounded by water
C. Both water and gases flow through the same tubes
D. There are no tubes
Answer: B
Fire-tube boilers have hot combustion gases passing through tubes surrounded by water .
6. The expansion tank in a hot water heating system is designed to:
A. Allow for expansion of water as it heats
B. Increase water pressure
C. Store hot water for later use
D. Reduce water temperature
Answer: A
As water heats, it expands. The expansion tank provides space for expanded water to
prevent pressure buildup .
7. What is the purpose of a safety valve on a steam boiler?
A. To regulate steam pressure during normal operation
B. To release pressure if it exceeds the maximum allowable working pressure
C. To add water to the boiler
D. To measure steam temperature
Answer: B
Safety valves are the final protection against overpressure and must be tested regularly .
8. What is "scale" in a boiler, and why is it dangerous?
A. Hard mineral deposits that act as an insulator, causing tubes to overheat
B. The weight of the boiler when empty
C. A layer of oil on top of the water
D. Rust on the outside of the boiler shell
Answer: A
Scale prevents water from cooling the tubes, allowing the fire to melt or weaken the steel .
9. What is "pitting" in a boiler's metal surfaces?
A. Small, deep holes caused by localized oxygen corrosion
B. Large dents caused by a hammer
C. Surface discoloration
D. Weld marks
Answer: A
Pitting is localized corrosion that creates small, deep holes in metal .
10. What is "primary air" in a burner?
A. Air mixed with fuel before it reaches the point of ignition
, 3
B. Air used to cool the boiler room
C. Air sucked up the chimney
D. Air coming through windows
Answer: A
Primary air starts combustion; secondary air is added later to complete the burn .
11. What does a steam pressure gauge measure?
A. Pressure inside the boiler in PSI above atmospheric pressure
B. Temperature of steam
C. Weight of steam in pipes
D. Volume of steam being used
Answer: A
Standard gauges show gauge pressure (psig); to get absolute pressure (psia), add 14.7 psi .
12. What is the function of a siphon (pigtail) in a steam pressure gauge installation?
A. To suck water into the gauge
B. To create a water seal that protects internal gauge parts from steam
C. To increase pressure reading
D. To drain the boiler
Answer: B
The siphon creates a water seal that protects the gauge from the high temperature of steam
.
13. When a low-pressure boiler is short-cycling repeatedly during peak heating hours,
what is the MOST appropriate first action?
A. Immediately shut down the boiler
B. Check the boiler's operating control settings and differential
C. Increase the boiler's firing rate
D. Bleed all radiators
Answer: B
Short-cycling is often caused by improper control settings. Verify and adjust settings before
escalating .
14. A Custodian Engineer notices a faint odor of natural gas in the boiler room. What is the
FIRST course of action?
A. Locate the main gas shut-off valve and close it
B. Ventilate by opening windows
C. Evacuate the area and call 911 from a remote location
D. Ignite a lighter to test for the leak
Answer: C
Any action that could create a spark poses ignition risk. Evacuation and calling from a safe
remote location is the mandated first step .
