Are you thinking of installing manual shutoff valves downstream from your electronic anti-siphon valves to turn off water to certain parts of your yard? This can work if some sprinklers don’t get shut off by the downstream valves. But in most cases, this is not something you should do.
The anti-siphon valve works by using a small air vent that is located on the downstream side of the actual valve. If you look closely at the anti-siphon valve, you’ll see that a large cap sits directly above the water outlet of the valve and that the air vent is under this. On the lower perimeter of the cap, you’ll see holes or slits that allow the air to move in and out of the vent.
When the anti-siphon valve shuts off the water, the pressure drops in the pipes downstream from it as the remaining water flows out of the sprinklers. As the pressure drops, the little air vent in the valve opens and allows air into the pipe right behind the valve. This air travels into the pipe and breaks any siphon effect so that water from the sprinkler can’t be drawn backward through the valve and into the potable water supply.
If you have a valve downstream of the anti-siphon valve, it will trap pressurized water in the pipe between the anti-siphon valve and the downstream valve and not allow it to depressurize. You should also be aware that sprinkler heads with built-in check valves will also hold the water pressure in the pipe. This is why you should remove the check valve from at least one of the sprinklers on each valve circuit when using anti-siphon valves.
Unfortunately, too many people still go ahead and do these kinds of installations on their irrigation systems only to find that the anti-siphon valve backflow prevention mechanisms fail. If you have doubts about whether or not you can safely install valves downstream of an anti-siphon valve, then contact South Austin Irrigation Repair. We provide the expert advice and service you need to optimize your irrigation system. Don’t take chances with your equipment: contact us today!
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