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cai 08-01-2011 12:14 PM

Anti Siphon faucet spewing water
Hi all,

I am in need of plumbing help...:(

I have a DIY sprinkler system that is connected to the outside frost free faucet (I live in an area where things freeze up in winter). The faucet has an anti siphon valve similar to this.

A bit of history:
Originally, when I installed the 3/4" sprinkler system, there were a bit of water hammer when the system stop. So I installed a 1" air column, 1ft long. The column is located below the faucet and above the electronically-controlled sprinkler valves. This removed the water hammer.

The problem:
Even though there is no more water hammer, whenever my sprinkler system stops, water spews out of the top of the anti siphon valve for a very brief time, maybe long enough for you to snap your fingers and it stop. (I attribute that to the sprinkler valves closing so water pressure going to the valves is forced back toward the anti siphon valve and leaks out, as it is designed to do). However, sometimes, it spews (for the same duration) and stop and spews out again and stop and again... Maybe 5-6 cycles per second. It keeps doing that until I manually turn off the water. While all of this spewing is going on, there is rattling and banging in the water pipes inside the house (which I believe to be minor water hammer).

Manual intervention kinda defeats the purpose of having an automated system. I'm afraid this would happen when I'm not home and it keeps going on for hours. I might come home to a flood in the basement if the pipes were to burst. So what is my problem? Is it because my air column is too short? Is the anti siphon defective? Do I have a cheap a$$ faucet? Is my water pressure too high? Is it something else?

More importantly, how do I fix it?


P.S not sure if it's relevant, but I have another faucet in the garage, also with anti siphon valve. I have a garden hose attached to that faucet and every time use the spray gun and let it go sharply, the faucet also spews water briefly.

TheEplumber 08-01-2011 02:48 PM

199 Attachment(s)
I suspect three things.
You have high water pressure.
Poorly designed arrestor.
Wrong use of the vacuum breaker
High water pressure is causing air in your air chamber to compress too much and sending slugs of water against the v b. That type of v b is not designed to have continuous pressure against it. Same goes for your faucet. Best to bypass the hose bib.

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