Unpressurized external buffer liquid system supplying clean fluid to the inboard and outboard seal faces.
- Used with Arrangement 2 seals.
- Buffer liquid shall be maintained at a pressure less than seal chamber pressure.
- Buffer liquid is circulated by an external pump.
- Plan 55 is similar to Plan 54 except the barrier liquid is unpressurized (buffer liquid).
- Process fluid is not contaminated.
- Near zero process emissions.
- Provides buffer liquid cooling and circulation even if the process pump is not active.
- Sensors and flowmeters may be added within the external system to readily identify seal failure based on support system conditions.