Anti-siphon vs vacuum breaker?

July 5, 2016 5:52 PM

Help an irrigation n00b! Is there a significant difference between these two hose attachments: a "Vacuum Breaker, Male Hose Thread" and a "Anti-Siphon Valve"? I need to make sure that the outdoor faucets attached to our house aren't draining water back into our drinking system, and I'm not quite sure if those two attachments do the same thing? Or is one better for a certain purpose than the other?

Here are the two attachments I'm looking at: Anti-Siphon Valve and the Vacuum Breaker.


For bonus points: we have an outdoor irrigation system and I'm not sure where it attaches to our water line (newish house to me), should I be using one of those two attachments on each end point (before the hose) to ensure no back flow from the system? (It would be great if the entire system had a industrial anti-siphon setup where it connects, but I'm not sure that is the case.)

posted by tigeri to Home & Garden (3 answers total)

A vacuum breaker is probably not what you want, or at least not the only thing you want. That only lets air in if you develop a negative pressure in the system. Which could prevent back-siphoning from a pool or something, but won't do anything if you get actual reverse flow by some other method (gravity, pressure from the other end). A check valve will block backward flow, but they're kind of unreliable and leak a small amount by while shutting (and crappy ones leak all the time).

You'd have to call your city to see what types of back flow prevention devices they require. Your house might already have a back flow prevention device at the main supply line. (Which means you should have a surge tank on your hot water heater, but one doesn't guarantee the other).
posted by ctmf at 6:28 PM on July 5, 2016

Cities I've worked in have required both a vacuum breaker on hose bibs and a backflow preventer when permitting substantial plumbing work, but that was in southern California. Anti-siphon valves weren't an option.
posted by LionIndex at 6:32 PM on July 5, 2016

Best answer: They are essentially the same thing from what I understand. You'll want to get something metal, not plastic (especially if you live somewhere where things freeze).

You may want to inspect your current hose bibs (the "faucet" part that comes out of the house) to see if 1.) it already has a vacuum breaker on it, or 2.) it is a hose-bib designed to require a specially threaded vacuum breaker (as required by some city codes) - I think only Arrowhead makes these, the male end on the hose bib will have a "fine" thread, and regular garden hose attachments will not fit.

If you have an Arrowhead style hose bib, you will need the Arrowhead vacuum breaker which will cost you an obnoxious amount of money (guess which kind I had on my new house).

The irrigation system on my house has a huge vacuum breaker assembly like this one, right near where the controls are. If you have one of those, it should be pretty hard to miss.
posted by sparklemotion at 9:05 AM on July 6, 2016