Barberi® check valves are monodirectional devices, allowing the backflow prevention of fluid under pressure. According to the model, they are normally used in domestic water installations, booster pump systems, heating systems, central heating systems, heat generators (wall-mounted boilers, solid fuel generators, heat pumps). Sealing is permitted through forces exerted by a spring and by the fluid pressure against a gasket which guarantees the seal even at very low back pressures. Moreover, the force of the spring allows the valve to have a universal characteristics concerning the installation position. The peculiarity of this range of valves is the presence of two check valves and a side drain (test port) between the two check inserts. The double check valve is necessary to create an intermediate safety chamber (like backflow preventers). This avoids that a fluid, coming back from the second check valve, can effectively enter into the upstream system. The test port is used to check the correct working of the downstream check valve. This valve can be used as antipollution device in systems with potable water.