When it comes to reliable gravity flow prevention, Taco's Flo-Chek series is the gold standard. Their design has been refined for the past four decades resulting in a compact, dependable addition to any hydronic heating system. The 218-3 is a cast iron, universal Flo-Check check valve with a 3/4" NPT connection. With Taco Flo-Cheks you'll never have to worry about heat going to an already satisfied zone again. If you use an indirect fired water heater with your boiler, a Flo-Chek is the perfect way to keep your space heating and your DHW production completely separate. Inefficient circulation and gravity flow are things of the past with Taco Flo-Cheks in your system.