The best kind of Flap Valves have a double seal, are self cleaning, and have flaps that cannot be over-rotated and left open. Vented Flap Valves allow a flow of air over the surface of the water which improves water quality and prevents a vacuum forming when large quantities of water are quickly drawn from the tank.
It is recommended that they be fitted with silicone and not glued. Rain Harvesting has a range of flap valves to suit 50mm, 90mm and 100mm pipe and/or tank overflow outlets.
