Red Seal Steamfitter/Pipefitter Practice Exam

What is the purpose of a drain trap?

1. To increase water flow

2. To prevent sewer gases from entering a building

3. To connect multiple pipes

4. To allow thermal expansion

The correct answer is: To prevent sewer gases from entering a building

The purpose of a drain trap is to prevent sewer gases from entering a building. Drain traps, commonly found in sinks, toilets, and other plumbing fixtures, hold a small amount of water which creates a barrier between the plumbing system and the living space. This water barrier prevents harmful gases from the sewage system from escaping into the home, thus improving indoor air quality and safeguarding the health of the occupants. The design of drain traps is critical for maintaining a hygienic environment, especially in areas where waste is disposed of. The water in the trap seals off the pipe, allowing wastewater to flow through while effectively blocking gases that could be noxious or harmful. The other options inadequately describe the function of a drain trap. Enhancing water flow would not be a primary function, as drain traps actually create a small resistance in the flow dynamics. Connecting multiple pipes is a task typically accomplished through fittings rather than traps, and while thermal expansion is an important consideration in plumbing, it is generally managed through expansion joints or loops rather than drain traps.