A double check valve protects against the risk of backflow and back siphonage contaminations. Floguard double check valves are a compact, lightweight solution ideal for all class 3 contamination risks are per water supply (water fittings) Regulations 1999. Available in DZR Brass or Nickel. Double check valves are called so because there are two valves inside which act as a safety feature. It’s extremely unlikely that both valves will fail. If one valve fails, the other acts to prevent backflow and contamination in the mains water supply. The valve contains a check cartridge which, under normal conditions, is held closed by pressure within the system. When vacuum conditions occur, the suction causes the check cartridge to open and air to flow through, equalising the pressure within the hot water heater.