Fluid dose dispensing apparatus

Apparatus for dispensing a dose of fluid, the apparatus comprising a dispensing vessel with a dispensing outlet, the vessel having a piston and a vessel wall defining a cylinder in which the piston may move under pressure from a first position to a second position, wherein the apparatus has a bypass passage, that extends through the piston and has a valve member that is opened by a valve actuating plunger in the piston that moves within the piston to push the valve open when the valve actuating plunger abuts a shoulder at or near the second position in the vessel wherein the shoulder at the second position is an annular shoulder, wherein the vessel has a first chamber proximate a dispensing outlet end of the vessel and a second chamber remote from the dispensing outlet end and a piston between the first chamber and second chamber whereby when the piston moves under pressure from the first position to the second position the bypass passage in the piston opens to allow the fluid in the second chamber to be transferred into the first chamber to mix with the contents of the first chamber.