What is the purpose of a common vent in plumbing?

The purpose of a common vent in plumbing is to serve as a vent for multiple fixtures. This type of venting system allows air to enter the drainage system, which is essential for maintaining proper pressure and ensuring that wastewater flows freely without creating suction that could trap the flow of water. A common vent connects the drainage pipes of various fixtures, allowing for the equalization of air pressure and preventing the formation of vacuum conditions in the plumbing system.

This method of venting is particularly effective because it reduces the number of individual vents needed for each fixture, thereby simplifying installation and providing better overall venting efficiency. In a well-designed plumbing system, the common vent helps to ensure that the traps in each fixture maintain their water seals, which prevents sewer gases from entering the habitable spaces of a building.