Metered dose valve

An aerosol metering valve comprising: (a) a valve stem movable between a rest position and a firing position comprising: a body portion comprising a circumferential sealing surface (b) a valve body comprising: a body wall, and an internal chamber defined at least in part by the body wall; and (c) a metering gasket having an inner periphery defining an aperture, being disposed near the most interior end of the internal chamber and being configured to be able to form a transient, substantially fluid-tight face seal against the circumferential sealing surface of the valve stem, where at the rest position of the valve stem, the body portion of the valve stem is located within the internal chamber and as the valve stem is moved from its rest position towards its firing position the circumferential sealing surface of the valve stem contacts the metering gasket to form a face seal thereby closing a metering chamber and thereafter further movement of the valve stem towards its firing position causes the metering gasket to deflect while maintaining the seal with the circumferential sealing surface of the valve stem; and wherein the metering gasket in an unbiased configuration is an annular disc having a substantially planar form and where the valve is constructed and arranged such that the inner periphery of the metering gasket is urged out of said substantially planar form at the rest position of the valve stem, or wherein the metering gasket is pre-biased into a dished-shape.