Rain Bird manufactures only the highest quality Anti-Siphon valves. Use Anti-Siphon valves in locations where the use of a pressure vacuum breaker (PVB) or a double-check valve is required by city codes to protect against back flow. Check your local city codes to determine what type of valves are required. Anti-Siphon valves are installed above ground and will prevent back flow if properly installed. Anti-Siphon valves should always be installed at least 6 in. above the highest head on the valve line and should never have another valve installed further down the line from the main valve. Our Anti-Siphon valves also feature our patented vacuum breaker-available for automatic or manual applications. All of our Anti-Siphon valves work with any standard sprinkler timer.