Abstract: There is disclosed a fluid flow control valve that provides a plurality of selectable, constant flow rates and that is ideally suited for use with oxygen breathing devices to supply a flow of oxygen to persons in respiratory distress. The valve is simple in construction and designed for minimum size and bulk while insuring accuracy of flow rates. The valve is provided with positive detent indication of the preselected fluid flow rate and can be used in any position on a supporting surface or on the regulator valve of the oxygen supply system. The valve comprises a valve body having a central cavity with a carriage plate received and rotatably supported therein. A first external port communicates with a fluid passageway that extends internally of the body and communicates with a pair of internal ports which are open to the cavity at spaced-apart locations. The carriage plate carries a plurality of orifice members which are of preselected, different orifice sizes and which extend through the carriage plate.