1. n. []

A vessel that separates the well fluids into gas and two types of liquids: oil and water. A three-phase separator can be horizontal, vertical or spherical. This type of separator is commonly called a free-water knockout because its main use is to remove any free water that can cause problems such as corrosion and formation of hydrates or tight emulsions, which are difficult to break. A free-water knockout is commonly called a three-phase separator because it can separate gas, oil and free water. The liquids that are discharged from the free-water knockout are further treated in vessels called treaters. Free-water knockout is abbreviated as FWKO.

See related terms: horizontal separator,  mist extractor,  spherical separator,  stage separation,  vertical separator