What is the purpose of a crown vent?

The crown vent plays a crucial role in maintaining the proper function of plumbing systems, particularly with respect to traps. Its primary purpose is to prevent the siphoning of traps, which can occur when there is a negative pressure in the drainage system. When water flows through pipes, it can create varying pressures, and without proper ventilation, traps can be emptied of water due to this siphoning effect. This is problematic because traps are essential for blocking sewer gases from entering the living space; if the water seal within a trap is lost, it can lead to unpleasant odors and potential health risks.

By providing an air outlet, the crown vent allows air to enter the plumbing system, thus equalizing pressure and preventing the siphoning action that could otherwise draw water out of the trap. In essence, it ensures that the trap remains filled with water, thereby maintaining its function as a barrier against sewer gases.