CO Residential Plumber Exam Questions
and Correct Answers (Verified Answers)
Plus Rationale 2027 Q&A| Instant
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1. What is the primary purpose of a plumbing trap?
A. To increase water pressure
B. To prevent pipe corrosion
C. To prevent sewer gases from entering a building
D. To increase drainage velocity
Rationale: A plumbing trap maintains a water seal that separates the
drainage system from the occupied space. This water barrier prevents
sewer gases and odors from entering the building through the fixture
drain.
2. Which fitting is commonly used to change the direction of a
drainage pipe by approximately 90 degrees?
,A. Coupling
B. Union
C. Quarter bend (90-degree elbow)
D. Reducer
Rationale: A 90-degree elbow or quarter bend changes the direction
of piping by approximately 90 degrees. Drainage systems generally
use fittings designed to provide smooth flow and minimize turbulence
and blockage.
3. What is the primary function of a venting system in a residential
plumbing system?
A. To increase water pressure
B. To supply hot water
C. To remove sediment from supply lines
D. To protect trap seals and allow proper drainage airflow
Rationale: Plumbing vents allow air to enter the drainage system,
equalizing pressure as wastewater flows. Proper venting helps
prevent siphonage or backpressure that could destroy fixture trap
seals.
4. Which material is commonly used for residential water
distribution piping?
,A. Cast iron only
B. Clay tile
C. Copper or approved plastic piping
D. Concrete pipe
Rationale: Copper and various approved plastic piping materials are
commonly used for residential potable-water distribution. The specific
material permitted depends on the applicable plumbing requirements
and application.
5. What does the term "DWV" stand for?
A. Domestic Water Valve
B. Drain, Waste, and Vent
C. Drain Water Vacuum
D. Distribution Water Vent
Rationale: DWV stands for Drain, Waste, and Vent. The DWV system
carries wastewater away from fixtures and provides venting to
maintain proper drainage-system pressure and trap protection.
6. What is the purpose of a cleanout?
A. To increase water pressure
B. To regulate water temperature
, C. To provide access for cleaning and servicing drainage piping
D. To prevent hot-water expansion
Rationale: A cleanout provides an accessible opening into a drainage
pipe. Plumbers can use cleanouts to insert drain-cleaning equipment
and remove obstructions without dismantling the piping system.
7. Which device is designed to prevent contaminated water from
flowing backward into the potable-water supply?
A. Pressure-reducing valve
B. Mixing valve
C. Gate valve
D. Backflow-prevention device
Rationale: Backflow-prevention devices protect potable water from
contamination caused by reverse flow. Different devices are used
depending on the type and degree of cross-connection hazard.
8. What is the primary purpose of a shutoff valve installed on a
fixture supply line?
A. To increase drainage flow
B. To allow the fixture to be isolated from the water supply
C. To vent the drainage system
D. To prevent trap siphonage
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 pipe corrosion
C. To prevent sewer gases from entering a building
D. To increase drainage velocity
Rationale: A plumbing trap maintains a water seal that separates the
drainage system from the occupied space. This water barrier prevents
sewer gases and odors from entering the building through the fixture
drain.
2. Which fitting is commonly used to change the direction of a
drainage pipe by approximately 90 degrees?
,A. Coupling
B. Union
C. Quarter bend (90-degree elbow)
D. Reducer
Rationale: A 90-degree elbow or quarter bend changes the direction
of piping by approximately 90 degrees. Drainage systems generally
use fittings designed to provide smooth flow and minimize turbulence
and blockage.
3. What is the primary function of a venting system in a residential
plumbing system?
A. To increase water pressure
B. To supply hot water
C. To remove sediment from supply lines
D. To protect trap seals and allow proper drainage airflow
Rationale: Plumbing vents allow air to enter the drainage system,
equalizing pressure as wastewater flows. Proper venting helps
prevent siphonage or backpressure that could destroy fixture trap
seals.
4. Which material is commonly used for residential water
distribution piping?
,A. Cast iron only
B. Clay tile
C. Copper or approved plastic piping
D. Concrete pipe
Rationale: Copper and various approved plastic piping materials are
commonly used for residential potable-water distribution. The specific
material permitted depends on the applicable plumbing requirements
and application.
5. What does the term "DWV" stand for?
A. Domestic Water Valve
B. Drain, Waste, and Vent
C. Drain Water Vacuum
D. Distribution Water Vent
Rationale: DWV stands for Drain, Waste, and Vent. The DWV system
carries wastewater away from fixtures and provides venting to
maintain proper drainage-system pressure and trap protection.
6. What is the purpose of a cleanout?
A. To increase water pressure
B. To regulate water temperature
, C. To provide access for cleaning and servicing drainage piping
D. To prevent hot-water expansion
Rationale: A cleanout provides an accessible opening into a drainage
pipe. Plumbers can use cleanouts to insert drain-cleaning equipment
and remove obstructions without dismantling the piping system.
7. Which device is designed to prevent contaminated water from
flowing backward into the potable-water supply?
A. Pressure-reducing valve
B. Mixing valve
C. Gate valve
D. Backflow-prevention device
Rationale: Backflow-prevention devices protect potable water from
contamination caused by reverse flow. Different devices are used
depending on the type and degree of cross-connection hazard.
8. What is the primary purpose of a shutoff valve installed on a
fixture supply line?
A. To increase drainage flow
B. To allow the fixture to be isolated from the water supply
C. To vent the drainage system
D. To prevent trap siphonage
