Abstract: A tangentially disposed inlet (22) discharges lighter and heavier fluids into a basin (A) causing the fluid mass in the basin to rotate at a rate proportional to the flow. A heavier fluid drain (36) or drains (44) removes most of the heavier fluid causing a free vortex to form above their inlets. This vortex causes an inward spiraling surface current to sweep the floating layer into the center of the vortex, but it lacks the downward velocity to draw it into the heavier fluid stream. A fluid flow controller (42 and 46) regulate this flow so that a depth is maintained that is related to the incoming flow such that the diameter of the concentric layers of lighter and heavier fluids surrounding the eye of the vortex remain essentially constant while the main flow rate slowly varies over a very wide range.A light fluid concentrate tube inlet (32) is placed at the eye of the free vortex. Flow to this tube causes a smaller, amplified, continuation of the main vortex to form.