# Question about Anti-Siphon valves



## remster (Jan 8, 2007)

When the water company is replacing main lines and they hookup the houses to the temporary service and backfeed into the outdoor hose valve. How does that work if the house has a Anti-Siphon valve such as this? Will it damage the valve?


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## Double-A (Jul 3, 2006)

It doesn't hurt a thing. The vacuum breaker is designed to be under pressure and not leak when it has a hose connected to it and turned on. It doesn't care which direction the water flows.

The way it works is when pressure is relieved, a diaphragm moves and allows air into the system. This prevents water from flowing by breaking the negative pressure pulling in water, by breaking the 'vacuum' created by the moving water. Its just like poking a hole in the side of a soda straw. It doesn't work so well. The bigger the hole, the worse it works.


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## The Coastal Craftsman (Jun 29, 2009)

The anti siphon taps I have fitted have all used non return/check valves so you would only be able to get water out in one direction. They would not be able to push water in the reverse direction. They are made like this for a reason. If the water main out side your house breaks or there's a massive demand for water in your area then water can not siphon back up into your water supply. As an example a hose in a septic tank, water has positive pressure unless there massive demand in water elsewhere in area then hose has negative pressure and siphons back into you main lines. Your main lines are now filled with septic tank waste.


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## remster (Jan 8, 2007)

Checked the specs of the valve it says 

"The Model 17 contains an integral backflow protection device which
protects up to 125 psi of backpressure and therefore does​not require and add-on vacuum breaker."


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