Use the PVC True Union Spring Check Valve, 1 in. IPS S X S to allow water to flow one-way through pipe and prevent backflow. The 1/2 lb spring lifts when the water pressure exceeds the spring weight to let water through and closes to prevent water from going the wrong way through the irrigation system. This easy-fit check valve connects two 1 in. slip end pipes as a part of a complete irrigation or other pressurized system. Prevents costly property damage, pipe corrosion, and system issues. Durable check valve is made of PVC plastic. Pressurized Spring is made of stainless steel. Washer and O-Ring are made of EPDM. Use fittings and other valves to set up a new irrigation system, expand an existing system, or make repairs.