It is important that you can completely rely on flap valves in case of flooding. A well-made flap valve does its job properly and quietly. People usually only realise the enormous importance of flap valves when the water rises or flooding occurs.
What is the purpose of flap valves? To let the outflow of water pass through and to stop the inflow of water. This type of valve can be applied in a lot of different situations and constructions, also because the valve is corrosion-resistant.