In many demanding oil-water separation systems, a coalescer filter element is often used in series with a separator filter element. The coalescer element coalesces tiny water droplets into large droplets, while the separator element uses hydrophobic material that allows oil to pass but blocks water droplets. This combination is known as a coalescer/separator system, achieving ultra-low residual water content of 5–10 ppm, and is widely used in aviation fuel and turbine oil purification.
