Buffalo 6 inch /150mm Non Return Valve Stainless Steel Door, Anti flooding valveBuffalo 150mm Non Return Valve, NRV150 150mm Buffalo Non Return valve with WRc Approval. Suitable for clay, PVC & cast iron pipe systems to suit installation within either an outlet or inlet of a drainage chamber. Secured into pipework within drainage chambers effectively discouraging rats and rodents from entering a property via a drainage system. Non return valve features Stops backflow of effluent into properties, businesses and homes during