Farmunion 5pcs New Fuel Non Return One Way Check Valve Petrol Diesel Aluminium Alloy (10mm) Professional grade non-return valve - Ideal for marine, automotive, caravans/RV, and agriculture Stable characteristics, high reliability. Arrow marked on valve, showing fluid flow direction, Prevents fuel from returning back to the tank and keeps it in the line. The life of Aluminum head for using is longer than plastic heads Easy installation and replacement.