What Is a Suction Scrubber Separator: Compressor Protection, Sizing and Design Answering the core question: What is a suction scrubber separator? A suction scrubber separator is a knockout vessel installed immediately upstream of a compressor whose sole purpose is to ensure that no liquid enters the machine. It is deliberately small and fast rather than large and efficient: a vertical vessel with a liquid holdup of only 1-3 minutes and a conservative Souders-Brown K factor of