Check the listing for details. Hydro-Rain 1/2" Blu-Lock Auto Drain Valve. Condition: New. Listed at 9.05 USD. The Blu-Lock 1/2" Auto Drain Valve inserts into the end of your run of Blu-lock 1/2" swing pipe. Allowing water to drain from irrigation lines helps prevent damage in case of unexpected freezing temperatures. The plastic automatic drain valve is designed to automatically drain the sprinkler lines when the water is turned off, once the pressure in your lines drops below 5 PSI. For use in outdoor cold water applications only.Quick Tip: When installing any type of auto drain or flush valve in your irrigation system we suggest digging out some of the soil beneath the valve and replacing with gravel for better drainage.Hydro-Rainoffers a new and better way for sprinkler installation. Everything you do from the valve out, you can now do faster and easier with Blu-Lock. With the Blu-Lock system you don't need primer, glue or clamps.