Plan 23 (API 682 process-side piping plan) is a closed-loop flushing and cooling system based on “internal recirculation within the seal chamber + cooler.” A circulation device inside the seal chamber (commonly a pumping ring or circulation sleeve) draws fluid from the seal chamber, sends it through a cooler for temperature reduction, and then returns it back to the seal chamber. This provides a lower and more stable operating temperature for the seal faces.
This arrangement reduces seal face temperature without additional pressurization, suppresses flashing/vaporization, and improves seal reliability. It is widely used in centrifugal pumps and other rotating equipment handling high-temperature services such as hot water (including boiler feedwater), hydrocarbons, and chemical fluids.
