Abstract: There is disclosed liquid flow control apparatus (particularly for use where the flow takes place in the form of drops over at least part of the flow path). A valve in the flow path is controlled by a servo system in dependence on the difference between desired and actual rate of flow signals. A linear to exponential signal converter sets the desired rate of flow signal which is displayed by means of two relatively movable display members one of which is movable to a position dependent on the desired rate of flow and carries a logarithmic scale which is juxtaposed with a logarithmic scale on the other member. For example, the other member may be movable to a position dependent on the size of the drops, and the volume rate of liquid flow for any given time can be read off from the juxtaposed scale. The apparatus also includes a throttle valve comprising two relatively movable throttling members positioned on opposite sides of a flexible tube.