Overview of Typical API Seal Flush Plans

Plan 11 recirculates process fluid from pump discharge through an orifice into the seal chamber. It is the most economical single-seal flush.
Suitable: Clean, non-flashing, moderate-temperature media.
Limitation: Not for fluids with solids or high tendency to vaporize.

Plan 23 uses an internal pumping ring to circulate seal cavity fluid through an external heat exchanger in a closed loop for cooling.
Suitable: Hot clean fluids like hot boiler feedwater.
Limitation: Only for clean media; proper venting required.

Plan 32 injects clean external fluid at higher pressure into the seal chamber to flush away abrasive solids and protect seal faces.
Suitable: Dirty, polymerizing or abrasive process media.
Limitation: External flush will dilute process fluid and bring extra running cost.

Plan 53 is a pressurized barrier fluid system for double mechanical seals. An internal pumping ring circulates barrier fluid from a pressurized reservoir, preventing hazardous process fluid leakage. Subtypes 53A/B/C handle different pressure ranges.
Suitable: Toxic, flammable, high-vapor-pressure fluids with low emission requirements.
Limitation: Requires regular pressure checks and barrier fluid refills.

Plan 54 is also for pressurized dual seals. Unlike Plan53, it uses an external pump to circulate barrier fluid, delivering stable flow independent of pump rotation speed.
Suitable: High-pressure critical service, low pump speed or multi-pump centralized systems.
Limitation: Higher upfront cost and more complex maintenance.