Double check valve

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.

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 valve reduces the pressure differential across the other, allowing a more reliable seal and avoiding even minor leakage.