A valve poppet (54) is provided for use in a regulator valve assembly (200) for regulating the pressure of a flowing gas through a gas flow pressure regulator (300). The valve poppet is includes a valve disc (54) having a flexible portion (60a) so as to permit upward and downward movement of a valve stem (52) in an axial direction. The valve disc may have an edge portion (60b) that provides a preloading force to self-align the valve disc within a valve seat (70), and axially constrain the motion of valve stem. The valve stem (52) may extend perpendicularly relative to the valve disc from a sealing portion (58). The movement of the valve stem is axially constrained and results in upward and downward movement of the flexible portion when the valve is opened and closed. The flexible and end portions of the valve disc may be formed of a plurality of spiral arms for self-aligning and axially constraining the valve disc.