A Breather Valve, also known as a Pressure & Vacuum Relief Valve, is a type of safety valve that is used to protect storage tanks, vessels, and pipelines from overpressure or vacuum conditions. The valve allows air to enter or escape the tank as necessary to maintain a safe pressure level and prevent damage or collapse of the tank.

Breather valves typically have a spring-loaded diaphragm that opens and closes based on the pressure inside the tank. If the pressure inside the tank exceeds the set pressure limit, the diaphragm opens, releasing excess pressure and preventing overpressure conditions. Similarly, if the pressure inside the tank falls below a certain vacuum level, the diaphragm opens, allowing air to enter and prevent the tank from collapsing.