3/4", Sure Flow Automatic Anti-Siphon 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 & BeforeStart 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.