Filter arrangement, within a circuit separated from the main flow, incorporating a separate pump and in most cases a twin filter .
This separation from the main circuit makes it possible to be very precise when defining the filter. Regardless of how long the system operates for, it can keep on working until the oil is perfectly clean. Bypass filtration can also be used to rinse out the main system.
Alternatives: filter in main conduit, partial flow filtration.
Image: Secondary-flow filtering