A Double Check Valve or double check assembly (DCA) is a backflow prevention device designed to protect water supplies from contamination. It is also a valve used in air brake systems on heavy trucks.
Usage in Water Supply: In the case of usage in water supply, it consists of two check valves assembled in series. This employs two operating principles: firstly one check valve will still act, even if the other is jammed wide open. Secondly the closure of one Angle Globe Valve reduces the pressure differential across the other, allowing a more reliable seal and avoiding even minor leakage.
The double check valve assembly is suitable for prevention of back pressure and back siphonage, but is not suitable for high hazard applications. It is commonly used on lawn irrigation, fire sprinkler and combi-boiler systems. If the hazard is higher, even a relatively low hazard such as using antifreeze in the fire sprinkler system, then a more reliable check valve such as a Reduced pressure zone device may be mandated.
With a ball check valve, there is a ball inside the shell that sits up tight against the side of the valve where the water will be coming from. In most cases, there is a spring that holds the ball tight up against the hole, creating a seal. When water is forced through the valve, it pushes the ball into the spring so that it can come through the opening and out the other side. When the water is turned off, the ball settles back against the hole and keeps water from flowing back the other way. A Dual Check Valve would have two areas within the valve with balls sealing them shut.
