Where the separation of vapors and liquids is required, a separator drum, or knockout pot, flash drum, or compressor suction drum, is integrated into the process unit. The separation vessel receives the flashing liquid mixture where the liquid is subsequently gravity separated and falls to the bottom as the vapor exits at the top.
Typically, a collection tank located beneath the separation chamber collects the liquid by gravity flow and utilizes a liquid level control for liquid withdrawal. The control also maintains a vapor barrier while discharging the collected liquid at the same rate of accumulation. In some separators, such as flash drums, liquid level must be kept within an extremely narrow span for very tight control.