Orbit, 51059, 3/4" ATMOSPHERIC VACUUM BREAKER with Female National Pipe Threads (FNPT) The Atmospheric Vacuum Breaker is designed to prevent contaminants from entering the main water supply through sprinkler heads. It is not designed to be used as a mainline anti-siphon device

A vacuum breaker is one of several devices intended to prevent water being fed into a faucet from getting back into the potable water supply, by flowing back into the pipe supplying the water. Vacuum breakers do this by preventing back-flow and back siphoning from occurring. Any place where water is supplied for any use other than drinking water needs a vacuum breaker installed.

Some State and Local Laws require one to be used before a Fertiilizer Injector on your Drip or Sprinkler Systems.