What is a non return valve? & what does it do? Comments Off on What is a non return valve? & what does it do? 18 Jan 2016 Vote Up 0 Vote Down Answered Public Public Private Technical Anonymous asked January 18, 2016 hi, what is a non return valve? & what does it do? 1 answer Vote Up 0 Vote Down Public ⋅ January 20, 2016 This is a valve that only allows the water to flow in one direction. #1 Please login or Register to Submit Answer