VACUUM BREAKER - C&D RUBBBER / 551a

A vacuum-breaker insert is a small plumbing device designed to prevent backflow—the unwanted reversal of water flow—which can contaminate the clean water supply.
When water is flowing normally (from a faucet, hose bib, or other outlet), the insert allows that flow to proceed. However, if a sudden drop in water pressure occurs (like from a burst main or fire hydrant usage), a vacuum can form and try to suck water back into the system. The vacuum-breaker insert breaks this vacuum by allowing air in, stopping the backward siphoning of potentially dirty water.
Vacuum breaker parts for flush valves replace the vented sleeve that stops backflow to prevent water supply contamination. Vacuum breakers sit below the diaphragm assembly of a flush valve (flushometer) to keep water from flowing backward through the valve during flushing. They typically need repair or replacement when they allow leaks through the vent holes.