A fluid flow control valve comprises (a) a high pressure region adapted to contain a fluid at its supercritical or nearcritical temperature and pressure conditions and connected via an orifice to a low pressure region, (b) a seat adjacent the orifice, (c) a sealing element positionable against the seat to form a seal between the high pressure region and the low pressure region, and (d) an electrically and/or electronically controlled actuator operable to move the sealing element against and/or away from the seat to allow control of fluid flow from the high pressure region to the low pressure region. In a specific embodiment, the high pressure region contains a fluid at its supercritical or nearcritical temperature and pressure conditions. The valve may be used, for example, to provide very low flow rates, for example, for supercritical fluid chromatography, supercritical fluid extraction, critical point drying, supercritical fluid cleaning, and supercritical fluid separation methods. In another embodiment, the valve is suitable for use in methods of delivering a biologically active substance to a patient in need thereof.
