Abstract: A fluid metering device mixes a predetermined quantity of a first fluid with a larger quantity of second fluid supplied to the device at a higher pressure on each cycle. The pressure of the second fluid provides the force necessary to motivate a first pumping means which on movement to an `outlet` position within a housing displaces the mixed fluids on an outlet side of the first pumping means to their destination. Movement of the first pumping means actuates a second pumping means which pumps a predetermined quantity of the first fluid into the housing on each cycle. On the maximum pumping stroke of the first pumping means being reached at the `outlet` position, a passage is opened in the first pumping means which is then restored to an `inlet` position, the second fluid in the housing passing through the passage during such restoration and thus being available for dispatch on the next pumping stroke.