Check Valve Elbow for US/RO

RO was constantly generating water going down the drain

Had no idea there was a check valve in the system. Well hidden in the elbow. Made of metal and my system is 9 years old, check valve was rusted and stem was corroded, so the spring was not held in place.This very well was my problem all along

parts

love my filter system. but it is getting a little old. need parts to keep it going