Product Description Hunter PGP Check Valve & Screen Assembly As air in the system piping can cause long-term damage to rotors and plumbing, the drain check valve keeps lines from draining when the system is shut off. This saves water, reduces liability, and increases system life. Fits PGP & I-20 Check Valves are for use in sprinkler heads that have low head drainage as a problem. The drain check valve keeps lines from draining when the system is shut off. This saves water, reduces liability, and increases system life. To Replace the Drain Check Valve: Remove the internal assembly from the case. Insert the large, irregular shaped end of the Drain Check Valve assembly into the bottom of the riser. The small circular rubber portion of the Drain Check Valve Assembly will remain outside of the riser. Replace the internal assembly and tighten it to the body. How to Fit Remove the rotor from the case and turn up side down,firmly push fit the check valve in the filter until it clicks with the rubber on the outside, re fit to the case. Click for Product Brochure