Toro PCV-500 1/2" NPT Precision Check Valve Adapter. Low head drainage can be seen in an elevation change of fewer than six inches. The resulting runoff and water waste can lead to landscape erosion, unsafe conditions on hardscapes and sidewalks, and pooling around spray heads. The Toro Precision™ Check Valve saves water and eliminates runoff by immediately sealing the spray head at its connection point at the end of the irrigation cycle, thereby preventing the draining of lateral lines through the lowest-lying heads.