Abstract: 1. A sensitive blocking valve device comprising a casing, said casing comsing a pair of half-shell members each including a mating surface at the outer periphery and each having an axial valve seat portion projecting into the interior of said casing and in mutual alignment, an axial orifice through the valve seat portion of each half-shell member, a metallic valve wafer comprising a central valving portion disposed to move to close either of said orifices in said valve seat portions of the casing and having an integral double spiral flat spring formed integrally therewith and extending from said central portion, and an annular portion at the outer periphery of said double spring and formed integrally therewith, said annular portion being disposed in clamped relation between said half-shell members, said wafer including said double flat spring and annular portion all being of the same uniform thickness and planar when the valve device is unoperated.