What is a type of backflow preventer that admits atmospheric pressure through ports?

A vacuum breaker is specifically designed to allow air to enter the plumbing system to prevent a vacuum condition, which can cause backflow of contaminated water into the potable water supply. It functions by admitting atmospheric pressure through ports when there is a drop in system pressure, thus breaking any potential vacuum that may form. This is crucial in applications where a siphoning effect could lead to backflow and contamination of the clean water supply, ensuring the safety of the drinking water system.

The other types of devices listed, such as check valves, backwater valves, and pressure relief valves, serve different functions. A check valve allows flow in one direction and prevents backflow but does not introduce atmospheric pressure. A backwater valve is specifically designed to prevent floodwater from entering the building through the drainage system. A pressure relief valve is used to release excess pressure in a system but does not function to protect against backflow or allow atmospheric pressure into the system.