A fluid flow control valve is disclosed. This valve includes a housing which defines a central passageway having fluid inlet and fluid outlet openings. A pressure responsive element is disposed within the passageway for selectively opening and closing the inlet opening to fluid flow in response to pressure exerted thereon at the inlet opening. A mechanism is provided within the passageway for exerting a bias force against the pressure responsive element sufficient to close the inlet opening to fluid flow absent a pre-established level of pressure exerted on the pressure responsive element in opposition to the bias force. Finally, a retainer device is positioned for removably securing the pressure responsive element and bias force exerting mechanism within the passageway.