What is the function of a weir in a three-phase separator?

• A. Weir provides a defined oil outlet and helps maintain separation by establishing a clear interface and preventing cross-flow between phases.
• B. Weir heats the oil to reduce viscosity.
• C. Weir filters solids from the oil.
• D. Weir measures the interface level.

Answer: (C)

The function of a weir in a three-phase separator is to create a defined oil outlet by letting oil overflow over a raised edge, which establishes a stable interface between the oil and the other phases. This arrangement helps keep water from mixing into the oil outlet and prevents cross-flow between the phases, preserving separation efficiency and a steady outlet level. The weir does not heat the oil or filter solids—heating is done by heaters and solids removal by filters or screens elsewhere, while interface level measurement is typically handled by level sensors. So the weir’s role is to provide a defined oil outlet and maintain separation by establishing a clear interface and preventing cross-flow between phases.