It does the same thing as the PCV valve in that it only allows flow in one direction (keeps pressure from entering the crankcase under boost and allows vapors to flow through the catch can under vacuum). It is a good fail-safe in case the factory PCV valve fails and most after market check valves react faster to changes in vacuum/pressure than the factory PCV valve can.Is his a good idea as an option on their OCC? What's the main purpose? Is it a good idea to get this?