This one way aluminum check valve is used to allow flow in one direction but not the other. The most common use is preventing fuel from returning to the tank after the pump is turned off, maintaining rail pressure. Another common use is as a vacuum line check valve to maintain accuracy of airflow measurement sensors or prevent pressure buildup. They can also be used with other materials including: Diesel Oil Water Coolant Air Gasoline Other materials compatible with aluminum Measures 2.4" in total length. Minimum differential pressure to open the valve in the direction of flow: 3 PSI Maximum differential the valve will hold: 90 PSI