Red Seal Gasfitter — Class B Practice Exam

What is the role of a gas vent cap?

1. To seal off gas lines when not in use

2. To prevent water entry while allowing exhaust gases to escape

3. To restrict airflow to the appliance

4. To enhance the gas pressure within the system

The correct answer is: To prevent water entry while allowing exhaust gases to escape

The role of a gas vent cap is primarily to prevent water from entering the vent system while still allowing exhaust gases to escape. This is crucial for maintaining the proper functioning of gas appliances and ensuring safety. If water were to enter the vent system, it could lead to corrosion, blockages, or even backup of exhaust gases, posing a significant safety hazard. Gas vent caps are designed with specific features, such as slanted tops or mesh screens, that effectively keep rain and moisture out while not hindering the flow of gases generated by combustion processes. This function is vital to ensure that harmful byproducts of combustion, like carbon monoxide, are efficiently directed away from the living spaces in a building. In contrast, sealing off gas lines or restricting airflow would hinder the operation of gas appliances. Enhancing system gas pressure is also not the function of the vent cap, as this would not relate to the venting process. Thus, the primary focus on allowing exhaust gases to escape while preventing water intrusion correctly identifies the essential role of the gas vent cap.