1-In. Automatic In-Line Sprinkler ValveUse In Line 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. In Line valves are installed below ground in a valve box down stream from the main line from a PVB or double check valve. In Line valves will not prevent back flow on their own: they need the help of a back flow