What is the function of a knock-out or drum separator?

• A. Remove bulk gas from the liquid stream
• B. Remove water from gas
• C. Remove solids
• D. Change API gravity

Answer: (A)

A knock-out or drum separator is a gravity-based device used to remove the bulk gas from a liquid stream. In operation, the liquid carries entrained gas; because gas is less dense, it tends to separate and rise to the top, where it exits through a gas outlet, while the liquid collects and exits the bottom. This leaves a liquid that is largely free of gas for downstream equipment, protecting meters, pumps, and separators from gas carryover and reducing slug flow.

It’s not meant to remove solids, change API gravity, or specifically dehydrate gas (that would be a water knockout or dehydration step), so those functions aren’t the primary purpose of this vessel.