BACK-FIRE PROTECTIVE UNIT

PROBLEM TO BE SOLVED: To provide a back-fire protective valve applied for combustible gas enabling a gas introduction passage to be stably shut off and at the same time enabling itself to be easily returned back to its original state when a temperature within a back-fire protective unit is increased due to back fire.SOLUTION: This invention relates to a back-fire protective unit comprising a check valve element 25 moving toward or away from a check valve seat 20D on the basis of pressure of combustible gas; a check valve spring 27 for biasing the check valve element 25; and a heat sensitive back-fire protective mechanism 3 for shutting off against flowing of combustible gas from a gas introduction passage 1A by back-fire heat characterized in that the heat sensitive back-fire protective mechanism 3 causes a heat sensitive shut-off spring 33 for moving the check valve element 25 to a check valve seat 20D for shutting-off the gas introduction passage 1A to be engaged with the check valve element 25 under movable state, a thermal deformation of thermoplastic resin causes the engaged state of the heat sensitive shut-off valve 33 to be released, the check valve element 25 to be pushed against the check valve seat 20D and then flowing of combustible gas to be shut off. 【課題】可燃性ガスに適用される逆火防止弁において逆火等により逆火防止器内が昇温した場合に、ガス導入路を安定して遮断するとともに、容易に復帰することが可能な逆火防止弁を提供すること。【解決手段】逆火防止器であって、可燃性ガスの圧力に基づき逆止弁座２０Ｄに進退する逆止弁体２５と、前記逆止弁体２５を付勢する逆止弁バネ２７と、逆火の熱によって、ガス導入路１Ａから可燃性ガスが流通するのを遮断する感熱逆火防止機構３とを備え、前記感熱逆火防止機構３は、前記逆止弁体２５を前記逆止弁座２０Ｄに移動させてガス導入路１Ａを遮断する感熱遮断バネ３３と、前記逆止弁体２５を進退自在な状態で係止し、熱可塑性樹脂が熱変形されることで前記感熱遮断バネ３３の係止が解除されて、前記逆止弁体２５を前記逆止弁座２０Ｄに押圧して可燃性ガスの流通が遮断することを特徴とする。【選択図】図２