Abstract: Fluid is metered into a conduit by a device which includes a detector for detecting the flow rate in the conduit, an amplifier for producing a pneumatic pressure which is dependent on the flow rate sensed by the detector, a control unit having a control shaft connected to a control diaphragm which is subjected to the pneumatic pressure from the amplifier, a motor unit having a hydraulically-pulsated motor/diaphragm connected to a motor shaft which is aligned with and contacted by the control shaft, and a pumping unit having a pump diaphragm connected to the motor shaft to meter fluid into the conduit.