BACK FLOW PREVENTING DEVICE

PURPOSE: To prevent a water leakage from a device by recovering the water drained from a back flow preventing chamber. CONSTITUTION: This back flow preventing device is provided with a back flow preventing chamber 5 having an inlet (water inlet), an outlet (water outlet), and a drain hole (drain port) 27, and the inside is substituted with air. The inside of the back flow preventing chamber 5 is made vacant to prevent the service water and miscellaneous water from being mixed with each other. A valve integrated with a check valve 6 and a back flow preventing chamber opening/closing valve 11 is arranged in the back flow preventing chamber 5. When the flow pressure is applied to the back flow preventing chamber 5, the drain hole (drain port) 27 is closed. When no flow pressure is applied, the drain hole (drain port) 27 is opened. A sump hopper 9 capable of storing the water in the back flow preventing chamber 5 and opened to the atmospheric air is integrally provided downstream of the drain hole (drain port) 27 below the back flow preventing chamber 5.