OCILB – Plumbing Contractor Examination
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 hot water from entering the drainage system
C. To prevent sewer gases from entering a building
D. To increase drainage pipe velocity
Rationale: A plumbing trap maintains a water seal that blocks sewer
gases from entering occupied spaces through the drainage system.
The trap must be properly installed and protected from siphonage,
backpressure, and other conditions that could destroy the seal.
2. Which fitting is generally used to change the direction of a drainage
pipe by approximately 90 degrees?
,A. Coupling
B. Union
C. Elbow
D. Reducer
Rationale: An elbow changes the direction of piping. In drainage
systems, fittings with appropriate sweep characteristics are generally
used so that wastewater can flow smoothly and the likelihood of
blockage is minimized.
3. What is the principal function of a cleanout?
A. To increase water pressure
B. To regulate temperature
C. To provide access for cleaning and clearing a drainage pipe
D. To prevent water hammer
Rationale: Cleanouts provide accessible openings into drainage piping
so that maintenance equipment can be inserted when blockages
occur. Proper placement and accessibility are important for
maintaining the drainage system.
4. Which device is commonly used to protect potable water from
contamination caused by backsiphonage?
,A. Pressure-reducing valve
B. Backflow prevention device
C. Water hammer arrestor
D. Expansion tank
Rationale: Backflow prevention devices protect potable water supplies
from contamination by preventing unwanted reverse flow. Different
devices are selected according to the type and degree of hazard
involved.
5. What is the purpose of a water hammer arrestor?
A. To remove sediment from water
B. To increase water velocity
C. To absorb pressure surges caused by sudden changes in water flow
D. To reduce sewer gas
Rationale: Water hammer occurs when flowing water is stopped or
redirected rapidly, producing a pressure surge. A water hammer
arrestor provides a means of absorbing that shock and reducing noise
and potential damage.
6. Which pipe material is commonly used for sanitary drainage
because of its corrosion resistance and relatively light weight?
, A. Cast iron only
B. Galvanized steel only
C. PVC
D. Copper tubing only
Rationale: PVC is widely used for drainage, waste, and vent
applications because it is lightweight, corrosion resistant, and
relatively easy to install. Its permitted applications depend on the
applicable plumbing code.
7. What is the primary purpose of a plumbing vent system?
A. To supply drinking water
B. To increase water pressure
C. To protect trap seals and allow proper drainage-system airflow
D. To heat the drainage system
Rationale: The vent system allows air movement within the drainage
system and helps prevent pressure conditions that could siphon or
blow water out of traps. Proper venting supports reliable drainage
and protects against sewer-gas entry.
8. What condition can occur when negative pressure in a drainage
system pulls water out of a trap?
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 hot water from entering the drainage system
C. To prevent sewer gases from entering a building
D. To increase drainage pipe velocity
Rationale: A plumbing trap maintains a water seal that blocks sewer
gases from entering occupied spaces through the drainage system.
The trap must be properly installed and protected from siphonage,
backpressure, and other conditions that could destroy the seal.
2. Which fitting is generally used to change the direction of a drainage
pipe by approximately 90 degrees?
,A. Coupling
B. Union
C. Elbow
D. Reducer
Rationale: An elbow changes the direction of piping. In drainage
systems, fittings with appropriate sweep characteristics are generally
used so that wastewater can flow smoothly and the likelihood of
blockage is minimized.
3. What is the principal function of a cleanout?
A. To increase water pressure
B. To regulate temperature
C. To provide access for cleaning and clearing a drainage pipe
D. To prevent water hammer
Rationale: Cleanouts provide accessible openings into drainage piping
so that maintenance equipment can be inserted when blockages
occur. Proper placement and accessibility are important for
maintaining the drainage system.
4. Which device is commonly used to protect potable water from
contamination caused by backsiphonage?
,A. Pressure-reducing valve
B. Backflow prevention device
C. Water hammer arrestor
D. Expansion tank
Rationale: Backflow prevention devices protect potable water supplies
from contamination by preventing unwanted reverse flow. Different
devices are selected according to the type and degree of hazard
involved.
5. What is the purpose of a water hammer arrestor?
A. To remove sediment from water
B. To increase water velocity
C. To absorb pressure surges caused by sudden changes in water flow
D. To reduce sewer gas
Rationale: Water hammer occurs when flowing water is stopped or
redirected rapidly, producing a pressure surge. A water hammer
arrestor provides a means of absorbing that shock and reducing noise
and potential damage.
6. Which pipe material is commonly used for sanitary drainage
because of its corrosion resistance and relatively light weight?
, A. Cast iron only
B. Galvanized steel only
C. PVC
D. Copper tubing only
Rationale: PVC is widely used for drainage, waste, and vent
applications because it is lightweight, corrosion resistant, and
relatively easy to install. Its permitted applications depend on the
applicable plumbing code.
7. What is the primary purpose of a plumbing vent system?
A. To supply drinking water
B. To increase water pressure
C. To protect trap seals and allow proper drainage-system airflow
D. To heat the drainage system
Rationale: The vent system allows air movement within the drainage
system and helps prevent pressure conditions that could siphon or
blow water out of traps. Proper venting supports reliable drainage
and protects against sewer-gas entry.
8. What condition can occur when negative pressure in a drainage
system pulls water out of a trap?
