This mechanical Seal flush plan is similar to API plan 11 the only difference is the fluid from the pump discharge is cooled by a cooler before the seal chamber as shown in the figure. This is the standard flush plan for hot water services such as used in boiler feed water pump. Efficient seal cooling with low cooler duty increase fluid vapour margin. This plan is used for high temperature service, hot hydrocarbons and Boiler feed water and hot water over 80oC.
API Flushing Plan 23
Seal cooler and piping must have air vents at highest elevation. The piping arrangement is shown below.
Piping System of Plan 23
Seal chamber requires close clearance throat bushing to isolate hot process fluid from the cold seal chamber flushing fluid. Regularly monitor cooler inlet and outlet temperatures for signs of plugging or fouling.