Diesel Engines generally use one of two types of lube filtration systems:
A Full Flow system
A Bypass or Part Flow system

A Full Flow system works the way it sounds. The entire flow of the fluid (oil, fuel, etc.) passes through the filter on its way to the engine.

In lube systems, the full flow filter is by necessity an open filter.
The full flow filter cannot restrict oil flow used to control larger particles, the full flow filter cleans all of the oil going to the engine.

A bypass or part flow system has a different flow path than a full flow
In a bypass system, a small amount of flow, usually controlled by an orifice, is taken from the main flow stream that oil is passed through a filter and then returns to the sump.

Due to the lower flow of a bypass system, a bypass filter can remove smaller particles.


Basic filter parts.

Filter Bypass Valve allows unfiltered oil to flow around (bypass) the filter. Not to be confused with a bypass filter Every lube system has a bypass valve.

May be part of the filter or part of the engine Antidrainback Valve Used for inverted applications maintains a head of oil to prevent dry starts. Used in conjunction with a standpipe.

Filter break down.