DRAIN PIPE BACKFLOW PREVENTION STRUCTURE AND BACKFLOW PREVENTION METHOD

To provide a backflow prevention structure etc. which has an immediate backflow prevention effect and can reliably prevent backflow in a drain pipe.SOLUTION: A backflow prevention structure 1 is provided with a knife gate valve 11 that can be opened and closed manually installed in a drain pipe 10 in order to prevent backflow in the drain pipe 10 extending from a building 2 to the outside, and a check valve 12 that opens and closes mechanically and is closed during backflow. In the event of flooding or other water disasters, the knife gate valve 11 is manually closed while the check valve 12 is closed during backflow in the drain pipe 10.SELECTED DRAWING: Figure 1 【課題】即時の逆流防止効果を有し、且つ排水管の逆流を確実に防止できる逆流防止構造等を提供する。【解決手段】逆流防止構造１は、建物２側から外に延びる排水管１０の逆流防止のために、排水管１０に、人力で開閉するナイフゲートバルブ１１と、機械的に開閉を行い、逆流時には閉状態であるチェック弁１２とを設けたものである。洪水等の水害時には、排水管１０での逆流時にチェック弁１２が閉じている状態で、ナイフゲートバルブ１１を人力により閉じる。【選択図】図１