IDPH – Plumber’s License Examination
(Journeyman Plumber) Questions and Correct
Answers (Verified Answers) Plus Rationale 2027
Q&A| Instant Download Pdf
1. What is the primary purpose of a plumbing trap?
A. To increase water pressure
B. To prevent sewer gases from entering a building
C. To increase drainage velocity
D. To eliminate the need for venting
Answer: B. To prevent sewer gases from entering a building
Rationale: A plumbing trap retains a small amount of water after each
fixture is used. This water seal prevents sewer gases and odors from
traveling through the drainage system and entering the occupied space.
2. Which component is normally installed to prevent contaminated
water from flowing backward into a potable water supply?
,A. Cleanout
B. Trap
C. Backflow prevention device
D. Air admittance valve
Answer: C. Backflow prevention device
Rationale: Backflow prevention devices protect potable water from
contamination caused by backpressure or backsiphonage. The specific
device required depends on the degree and type of hazard.
3. What is the primary function of a plumbing vent system?
A. To supply hot water
B. To increase water pressure
C. To protect trap seals and allow proper drainage-system airflow
D. To collect stormwater
Answer: C. To protect trap seals and allow proper drainage-system
airflow
Rationale: Proper venting allows air to enter and leave the drainage
system so pressure fluctuations do not siphon or blow trap seals. It also
promotes proper drainage flow.
,4. Which fitting provides the least desirable change of direction for a
horizontal drainage system?
A. Long-sweep elbow
B. Wye fitting
C. Sanitary tee used horizontally
D. Combination wye and eighth bend
Answer: C. Sanitary tee used horizontally
Rationale: A sanitary tee is designed primarily for connecting a
horizontal branch to a vertical drain or vent. It should not generally be
used to make a horizontal-to-horizontal change of direction because its
geometry can interfere with drainage flow.
5. What is the main purpose of a cleanout?
A. To regulate water temperature
B. To provide access for cleaning and maintaining drainage piping
C. To prevent water hammer
D. To increase fixture-unit capacity
Answer: B. To provide access for cleaning and maintaining drainage
piping
, Rationale: Cleanouts provide accessible openings through which
drainage piping can be inspected, rodded, or otherwise cleaned when
blockages occur.
6. Which condition is most likely to cause a trap to lose its water seal
through siphonage?
A. Excessive positive pressure in the water supply
B. Improper or inadequate venting
C. Oversized water piping
D. Low water temperature
Answer: B. Improper or inadequate venting
Rationale: When a drainage system is not properly vented, discharge
from one portion of the system can create negative pressure that
siphons water out of another fixture's trap.
7. What does the term “water hammer” describe?
A. Expansion of a pipe caused by freezing
B. A pressure surge caused by rapidly stopping flowing water
C. A reduction in water pressure caused by elevation
D. A sewer blockage caused by grease
(Journeyman Plumber) Questions and Correct
Answers (Verified Answers) Plus Rationale 2027
Q&A| Instant Download Pdf
1. What is the primary purpose of a plumbing trap?
A. To increase water pressure
B. To prevent sewer gases from entering a building
C. To increase drainage velocity
D. To eliminate the need for venting
Answer: B. To prevent sewer gases from entering a building
Rationale: A plumbing trap retains a small amount of water after each
fixture is used. This water seal prevents sewer gases and odors from
traveling through the drainage system and entering the occupied space.
2. Which component is normally installed to prevent contaminated
water from flowing backward into a potable water supply?
,A. Cleanout
B. Trap
C. Backflow prevention device
D. Air admittance valve
Answer: C. Backflow prevention device
Rationale: Backflow prevention devices protect potable water from
contamination caused by backpressure or backsiphonage. The specific
device required depends on the degree and type of hazard.
3. What is the primary function of a plumbing vent system?
A. To supply hot water
B. To increase water pressure
C. To protect trap seals and allow proper drainage-system airflow
D. To collect stormwater
Answer: C. To protect trap seals and allow proper drainage-system
airflow
Rationale: Proper venting allows air to enter and leave the drainage
system so pressure fluctuations do not siphon or blow trap seals. It also
promotes proper drainage flow.
,4. Which fitting provides the least desirable change of direction for a
horizontal drainage system?
A. Long-sweep elbow
B. Wye fitting
C. Sanitary tee used horizontally
D. Combination wye and eighth bend
Answer: C. Sanitary tee used horizontally
Rationale: A sanitary tee is designed primarily for connecting a
horizontal branch to a vertical drain or vent. It should not generally be
used to make a horizontal-to-horizontal change of direction because its
geometry can interfere with drainage flow.
5. What is the main purpose of a cleanout?
A. To regulate water temperature
B. To provide access for cleaning and maintaining drainage piping
C. To prevent water hammer
D. To increase fixture-unit capacity
Answer: B. To provide access for cleaning and maintaining drainage
piping
, Rationale: Cleanouts provide accessible openings through which
drainage piping can be inspected, rodded, or otherwise cleaned when
blockages occur.
6. Which condition is most likely to cause a trap to lose its water seal
through siphonage?
A. Excessive positive pressure in the water supply
B. Improper or inadequate venting
C. Oversized water piping
D. Low water temperature
Answer: B. Improper or inadequate venting
Rationale: When a drainage system is not properly vented, discharge
from one portion of the system can create negative pressure that
siphons water out of another fixture's trap.
7. What does the term “water hammer” describe?
A. Expansion of a pipe caused by freezing
B. A pressure surge caused by rapidly stopping flowing water
C. A reduction in water pressure caused by elevation
D. A sewer blockage caused by grease
