API Plan 21 (Cooled Flush) is a mechanical seal flush and cooling arrangement. It uses process fluid from the pump discharge for self-recirculation. The fluid passes through a flow control orifice and enters a cooler. After cooling, it returns to the seal chamber.
This circulation provides continuous cooling, lubrication, and flushing for the seal faces. No external flush fluid is required. The system increases the temperature margin in the seal chamber and helps reduce vaporization and flashing risks.
API Plan 21 also helps minimize coking in high-temperature services. It improves seal stability and supports reliable operation. The system is widely used for centrifugal pumps and other rotating equipment in medium- to high-temperature applications.
