A valve apparatus which comprises a main valve body and a main valve seat detachably abutting against each other to open and close a main fluid pass defined therebetween, and wherein, as measured from the longitudinal section of the valve apparatus, the detachably abutting plane of the main valve seat has a larger curvature radius than that of the main valve body in order to let a fluid stream conducted through the main fluid pass flow along the surface of the main valve seat; and that part of the surface of the main valve body defining one side of the main fluid pass with the main valve seat which faces the throat section of said main fluid pass is provided with a sharp edge at its end portion to allow for the easy removal of a main fluid stream from the main valve body.