Breather valves, also known as direct-acting vacuum/pressure relief valves, are a specialised type of valve designed to protect enclosed containers and tanks. These valves come in various types, including vacuum-only, pressure-only, and combination pressure and vacuum valves, and are available with flanged outlets or outlets vented to the atmosphere.

The valves are suitable for installation in bulk-enclosed containers and tanks to minimise evaporation loss and prevent excessive vacuum or pressure build-up within the container. Installing valves within tanks to control vacuum levels and pressure and prevent system unbalance and prevent physical damage or deformation of large-capacity storage containers