Helix External Check Valve AssemblyExternal check valve assembly for Helix Pond Skimmer. In the instance that the power shuts off to your home and you do not have a check valve on your pond; there is a large possibility that your pond is going to flood. There is a lot of water in the lines above your pump leading to your waterfall body. Having an external check valve will prevent this backflow from happening. Call 909 794 5217 for more questions