The manual anti-siphon valve features a combination of an inline forward flow valve and an atmospheric vacuum break which prevents water flowing from the irrigation system into the culinary system. This type of valve is most common in California. In other states it is common for a single backflow prevention device to protect the entire system at the mainline point of connection. In order to function properly, an anti-siphon valve should be installed at least 12 in. above the highest head in the zone which it controls. This typically requires the anti-siphon valve to be installed above-ground on risers. The anti-siphon valve features an easy-to-rotate flow control handle. We recommend that you use a steel sprinkler key for hard-to-reach places and PVC-Lock fittings for fast, glue-free installation. For outdoor irrigation use with cold water only.