1, Sure Flow Automatic AntiSiphon Valve, Professional Grade, With Flow Control, Reverse Flow Design Helps Prevent Flooding In The Event Of Internal Diaphragm Failure, Keeping The Valve Closed Saving Water, After Installation Before Start Up, Always The Flush System Of Dirt Debris Manually Using The Valve’s External Bleed Screw, Adjustable Flow Control Helps Prevent Wasteful Misting When Water Pressure Is Too High, A Top Mounted, Easy Turn Flow Control Knob Allows You To Optimize Flow To The Zone, Permitting Sprinklers To Water At Their Most Efficient Rate For More Uniform Coverage