Non-return valve
Culvert, screen and outfall manual, (CIRIA C786) published by CIRIA in 2019, defines a non-return valve (check valve or flap valve) is: ‘A one-way valve that normally allows fluid to flow through it in only one direction. In watercourses it is usually a top-hinged gate designed to close when downstream water level exceeds the upstream water level. Frequently used for drainage outfalls into tidal waters and rivers to prevent backflow.’
The Illustrated Guide to Hot and Cold Water Services (BG 33/2014), written by Reginald Brown and published by BSRIA in 2014, it suggests that a check valve (non-return valve): ‘Allows flow of water in one direction only. Located downstream of cold and/or hot water risers in apartments.’
It suggests that a double check valve (double non-return valve): 'Allows flow of water in one direction only. Located prior to outside taps or other hose connection points.'
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