the relief property of the second valve 20 ensures that the pressure that can be induced within the delivery reservoir cannot exceed a predetermined level and this serves to prevent inflation of the delivery reservoir 18 beyond its maximum volume this relief property of the first valve 17 also serves to ensure that on activation of the pump 15 when the delivery reservoir 18 is at it 39 s maximum volume the contents of the chamber of the pump chamber 15 will be returned to the holding reservoir 11 the delivery reservoir 18 is connected to an outlet 21 which may take any desired form according to the application of the delivery means through an outlet line 22 the outlet line 22 is provided with a flow restriction means 23 which comprises a means of ensuring a controlled flow from the delivery reservoir 18 to the outlet 21 the flow restriction means is formed with a plurality of passageways and may comprise an element having a plurality of capillary passageways or may comprise a porous element formed of glass ceramic or a like inert material which is able to withstand the pressure created in the outlet line 22 by the delivery reservoir 18 such that a controlled quantity of fluid is allowed to pass through the flow restriction means the difference in volume of the delivery reservoir 18 between its second volume and its.