A pressurized external spacer fluid system provides a clean spacer fluid to the isolated seal chamber, and it suits for the plan54 pressurized dual seal.
The spacer fluid pressure should be kept higher than the seal chamber pressure. It should not be used in the case where the spacer fluid pressure is lower than the pumping medium pressure to prevent the whole spacer fluid system from being polluted when the seal is failed.
The circulation of the spacer fluid is finished by an external pump or a pressurized system. The system is relatively complicated and expensive.