PROBLEM TO BE SOLVED: To provide a check valve capable of reliably checking a reverse flow regardless of the magnitude of differential pressure in a reverse flow direction and of suppressing the occurrence of permanent set of a valve body to improve the durability.SOLUTION: A disc-shaped valve body 15 having flexibility is arranged in a valve chamber 12, and a valve seat 13 of a first stage which has a large diameter and is configured by an intersection corner of surfaces 122, 123 as a valve seat and a valve seat 14 of a second stage which has a small diameter at a depressed position and is configured by an intersection corner of surfaces 124, 125 are formed. If intake air negative pressure in a forward direction J acts, an outer circumferential side of the valve body 15 is deflected and air is supplied from an intake passage part 814 to a downstream side passage 76. If small differential pressure acts as reverse flow differential pressure in the reversed direction K, a center of the valve body 15 is slightly deflected and is seated on the valve seat 13 of the first stage, and if high differential pressure acts, the center is further deflected and the valve is seated on the valve seat 14 of the second stage to check the reverse flow.COPYRIGHT: (C)2012,JPO&INPIT【課題】 逆流方向の差圧の大小の如何に拘わらず確実に逆止することができ、しかも、弁体のへたり発生を抑制して耐久性の向上を図り得る逆止弁を提供する。【解決手段】 弁室12に撓み性を有するディスク状の弁体15を配設し、弁座として面122,123の交差角部により構成される大径の第1段目の弁座13と、面124,125の交差角部により構成され凹んだ位置の小径の第2段目の弁座14とを形成する。順方向Jの吸気負圧が作用すれば弁体15の外周側が撓んで吸気通路部814から下流側通路76に空気を供給する。逆方向Kに逆流差圧として小差圧が作用すれば弁体15の中央部が僅かに撓んで第1段目の弁座13に着座し、大差圧が作用すればさらに撓んで第2段目の弁座14に着座して、逆止する。【選択図】 図10
