during storage and so that there is no risk of the dose of fluid being reduced due to prolonged storage because during storage the metering chamber 11 is empty and does not contain any fluid in the present invention the metering chamber 11 fills only when the valve member 20 which slides in the valve body 10 moves from its rest position shown in fig1 to its dispensing position shown in fig3 the metering chamber 11 is filled between said rest position and said filling position in the intermediate position shown in fig2 for this purpose the valve member 20 has a link channel 15 forming a passageway between the metering chamber 11 and a filling chamber 12 provided in the valve body 10 the link channel is closed when the valve is in the rest position in which said channel is disposed entirely within the metering chamber 11 similarly said channel 15 is closed when the valve is in the dispensing position in which said channel is disposed entirely within the filling chamber 12 it is only in the intermediate position shown in fig2 that the link channel 15 connects the filling chamber 12 to the metering chamber 11 as shown in the figure the link channel 15 may have an inlet 15 a and an outlet 15 b said inlet 15 a being disposed in the filling chamber 12 and said outlet 15 b being disposed in the metering chamber 11 when the valve is in the intermediate position when the valve member 20 reaches the intermediate position in which the link.