A movable valve for a valve assembly is described. The present valve comprises a plug attached to an immovable mounting flange by at least two non-resilient spider-like legs comprising first and second rigid leg segments that meet at hinging apexes positioned higher than the plug. The plug resists vertical displacement by virtue of the stiff leg segments having appropriately configured curvature and length. Actuation of the valve is through vertical displacement of the plug against the biasing forces, wherein displacement of the plug causes bowing of the legs without any stretching or change in the length of the leg segments.