Crankcase ventilation system

A crankcase ventilation system is a one way passage for gases to escape in a controlled manner from the crankcase of an internal combustion engine.

This is necessary because internal combustion inevitably involves a small but continual amount of blow-by, which occurs when some of the gases from the combustion leak past the piston rings (that is, blow by them) to end up inside the crankcase, causing pressure to build up in the crank case. For control of the pressure inside it, a PCV (positive crankcase ventilation) valve is used to vent the crankcase.