Hunter HCV Check ValveLow head drainage is a common issue in many irrigation systems. Elevation changes are something that must be carefully considered for optimal operation of any irrigation system. Eliminate low-head drainage for both rotor and spray shrub systems with the adjustable Hunter Check Valve. Hunter HCV check valves are designed with flexibility in mind. This adjustable check valve can hold back 4' to 32' of head, making them the most versatile check valve on the market today. Features:Variety of inlet/outlet options: 1/2" & 3/4" female inlet/male outletEasy adjustment access from the top of the valve with a flat-blade screwdriverMaximum flexibility: Adjusts to compensate for elevational changes up to 32'Durable and long lasting: constructed to meet schedule 80 specificationsEasy to install between riser and sprinkler Hunter HCV Check Valve Adjustment Instructions:Check Valve comes preset from factory at 12 feet of head. Adjustment can be made before installation or after without removing the sprinkler head.Insert a large flat-blade screwdriver in the outlet side of the check valve and turn the plastic screw clockwise to increase the check height or counter clockwise to reduce the check height. Increasing check height increases opening pressure; decreasing check height decreases opening pressure.To adjust the check valve when the sprinkler is already in place you must unthread the sprinkler body cap, pull out the sprinkler's internal parts. Insert the screwdriver straight through body and the inlet of sprinkler, and you will get right to the adjustment on the check valve. If you have a check valve installed below ground, this eliminates the need to unthread the sprinkler should you want to adjust the check height at a later time.The adjustment range is from 4' - 32' with opening PSI from 2 to 17. Each full turn of the adjustment screw elevation check height 4 feet and changes pressure by approximately 2 PSI.