Disclosed herein is a paint circulation system for a painting line, comprising a supply channel, a return channel and a plurality of drop lines downstream of the supply channel and upstream of the return channel, a paint pump means for circulating paint through the supply channel, the drop lines and the return channel with a corresponding flow rate through each drop line, and means for establishing a flow controlling pressure differential between the supply channel and the return channel in each drop line which is directly proportional to the paint flow rate, wherein a change in the flow controlling pressure differential in a given drop line causes a corresponding proportional change in the paint flow rate through the given drop line.