The official online store for Rain Bird Corporation selling the complete line of genuine Rain Bird sprinklers, timers, valves, drip, nozzles, accessories and replacement parts..Visit the Home Depot to buy Orbit in. Plastic FPT Automatic Anti Siphon Zone Valve.Anti Siphon Valves. An anti siphon valve is essentially a valve atmospheric backflow prevention device combined into one. In irrigation, these valves serve two purposes..Anti siphon valves may not be used as backflow preventers for a downstream valve manifold. Do not install valves after them. De.ed explanation why..