JOHN GUEST 1/4" One Way Check Valve RO Reverse Osmosis Water Filter NSF Certifie the Super Speedfit acetal Single Check Valve ensures protection against reversal of flow They are designed for conenction to either plastic or soft metal tube and they are intended for liquids only. Note that they are not suitable for air and vacuum applications The inner valve is spring loaded and the fitting produces low headloss It is also recommended that the non-return valve is regularly checked and maintained. Pipe connection has never been easier than with John Guest fittings