Table of Contents: How Do Anti-Siphon Valves Work?
What Is an Anti-Siphon Valve?
Anti-siphon valves are specialized irrigation valves that include a built-in backflow prevention device. Their main purpose is to prevent water from flowing back into your potable water.
Anti-siphon valves are considered simpler and less expensive than many other types of backflow preventers. Because of this, they are commonly used in residential sprinkler systems, where the water demand and regulatory requirements are less stringent than in commercial settings.
Anti-Siphon Valves Prevent Back Siphonage
Anti-siphon valves only allow water to flow in one direction. For irrigation purposes, it prevents water from the system from being siphoned back into the water supply line. Essentially, it stops unsafe water from entering a clean water supply, such as the water that comes from your faucets or shower heads.
This can be particularly dangerous in situations where something like a fertilizer injection system is being used to apply fertilizer through the sprinklers to the grass. An anti-siphon valve prevents the water currently resting in the sprinkler system’s pipes from being siphoned back into the home, where it could be emitted from a faucet and consumed.
Although some are much more complex, anti-siphon valves can be as simple as a spring-loaded one-way valve, which opens when water pressure is applied to it in one direction, but closes and seals when water pressure is applied from the other direction. Most cars now have anti-siphon valves in place to prevent gasoline theft.
How Does an Anti-Siphon Valve Work?
An anti-siphon valve combines the benefits of a backflow preventer with the functionality of a standard irrigation control valve. When the valve is turned on, water flows through the system and comes out of any connected sprinklers and drip emitters. When the valve shuts off, the anti-siphon mechanism kicks in.
Anti-siphon valves utilize a small air vent or vacuum breaker that reacts to changes in pressure. When the water is flowing, the vent is sealed to keep water moving through the system. When the valve shuts off, the drop in pressure opens the vent, allowing air into the line. This prevents dirty or contaminated water from being siphoned backward into your home’s clean water supply.
For the mechanism to work properly, the valve must be installed above ground and higher than all of the sprinklers or emitters it controls. Installing it too low or underground can prevent the air vent from opening correctly, leaving your system unprotected.
Installing an Anti-Siphon Valve
Now that we’ve discussed some of the benefits of an anti-siphon valve, let’s review the steps necessary to install one. As mentioned above, anti-siphon valves are relatively common in residential irrigation systems, so the setup process isn’t very complex.
- Start by choosing a location to install your valve. Position it near the water supply line, above ground, and at least 6 to 12 inches higher than the highest sprinkler head or drip emitter.
- Cut into the PVC or copper pipe if you need to attach a riser or short vertical section of pipe to bring the line above ground.
- Install the anti-siphon valve by screwing in the threads or using PVC cement to make a secure, leak-free connection. Ensure the valve is oriented correctly before proceeding.
- Test the system by slowly turning the water supply back on.
Keep in mind that these types of valves must be installed above ground and above the highest sprinkler head to work properly. Without this careful distinction, your valve won’t be able to prevent backflow. Anti-siphon valves are typically used for smaller residential systems, not large or high-pressure irrigation setups, but on some rare occasions, local plumbing codes may require a more robust backflow preventer instead.
If your irrigation system is especially large, you may need more than one anti-siphon valve. Usually, one is installed for each irrigation zone, not one for the entire system.
Built-In Backflow Protection
An anti-siphon is a type of backflow preventer and is an essential part of any commercial plumbing installation that is connected in any way to a potable water source. They are required by building codes everywhere. If you’re planning to install or replace an anti-siphon valve of your own, SprinklerWarehouse.com is a great place to start.
