The Barnes & Jones 3875 3/4" NPT Vacuum Breaker is a reliable plumbing safety component designed to prevent unwanted vacuum conditions in hydronic heating and boiler systems. It works by allowing air to enter the piping when negative pressure develops, helping prevent backflow and potential damage to system components. Commonly used with boilers, water heaters, and hydronic HVAC equip... https://www.partshnc.com/3875-barnes-jones-34-vacuum-breaker-for-steam-125-psi-max