What is the primary purpose of a trap in plumbing?

The primary purpose of a trap in plumbing is to keep sewer gases from entering a structure. Traps are designed with a U-shaped bend that holds a small amount of water. This water acts as a barrier, preventing harmful sewer gases from escaping the drainage system and entering living spaces. It is a crucial plumbing feature that helps maintain indoor air quality and ensures safety by blocking unpleasant odors and toxic gases that may be present in the sewage system.

While preventing backflow is important in plumbing systems, it is not the primary function of a trap; specialized devices like check valves are designed specifically for that purpose. Maintaining system pressure is typically associated with pressure-regulated systems rather than traps, and traps do not facilitate water flow; instead, they momentarily hold water to create the necessary seal against gases.