Abstract: A valve for maintaining constant fluid flow under conditions of a specified operating inlet pressure and varying inlet pressures in excess of the specified pressure includes a tubular valve body having a fluid flow channel extending between an inlet and outlet. The fluid flow channel includes a first flow path having a first variable volume and cross-sectional area, and a second flow path having a second variable volume and cross-sectional area. The valve further includes an fluid discharge orifice whose cross-sectional area less than the minimum of the first or second variable cross-sectional areas. If the inlet pressure is above or below the specified operating pressure, the variable volumes are caused to change to maintain a substantially constant fluid flow from the valve.