SpudFiles

I just found out about these valves while seaching ACE hardwares website. I think they use pistons, after seaching them up in google, they are called anti-siphon valves. Link to the place in ACE were I found them: http://www.acehardware.com/product/inde ... 7061231233

i think it uses a diaphragm.

anyway, my normal water master inline valve says that too. all it means is that dirt and moss and stuff like that wont go in.

at least i think thats what it means, i could be wrong.

They are nothing more than a sprinkler valve with another 90* turn in it.
They can be modded firther to help prevent the air from taking too many turns by drilling a hole on the anti-siphon side(black)(not the valve part)
take it apart and you'll see.

I'm pretty sure that the "anti-siphon" valve is basically a back flow valve (though the exact workings are a bit different).

The reason it is there is to prevent water from flowing backwards through the valve and contaminating the city water supply.

All household water suppllies, IIRC, are required to have a backflow valve. Usually, where the house's water pipe connects to the city main.

On a sprinkler valve the anti-siphon feature prevents dirty water from being sucked back into your household water supply if the supply pressure drops too low.

I had one of those on my original gun. They are just diapraghm valves contanied in a u bend shape. I have been told that in-line sprinklers work better, and after i switched to an in-line i would say my gun got somewhat of a power boost.