Reverse osmosis systems used with an auto shut off valve require a check valve to prevent backflow. This allows pressure to build up so the auto shut off can activate and shut the system off. Systems that continually run water down the drain may be missing or have a bad check valve, and systems that intermittently turn on without any water use may indicate a worn check valve.The check valve components are made of high quality stainless steel.The 1/8" threaded end connects directly to most membrane housings.The 1/4" quick connect fitting fits standard 1/4" tubing used on most RO systems.The 90-degree elbow angle allows for tight fits on the membrane housing.Replacement check valve elbow for reverse osmosis (RO) water filter systems1/8" male NPT threads fits most standard membrane housings1/4" quick connect allows you to easily connect to your current 1/4" poly tubingSymptoms of faulty check valve could be storage tank not staying full or excess water down the drain line