Volvo EPA2007 D13F Reference Manual page 100

94 ENGINE COMPONENT AND LOCATION
Lubricant becomes a mist in many areas of the engine as the result of the motion of
the parts (e.g., rocker arms, pistons, crankshaft, camshaft and rocker shaft). The mist
rides the drafts of air and other gases that circulate in the open spaces in the engine.
To prevent pressure buildup, the open spaces are ducted through a pipe that opens to
the atmosphere near the bottom of the engine.
The crankcase ventilation (CCV) system separates the oily mist from the gases
by centrifugal force. The oil returns to the oil pan. The remainder escapes to the
atmosphere.
A turbine in the CCV separator, driven by a small stream of oil striking its fins, spins
at high speed. The mixture of gases and oily mist trapped in the valve cover and
the timing gear cover drains onto the top of the center of the turbine and runs down
onto several discs rotating with the turbine. Separation occurs as the mixture, flung
outward by the turbine, strikes the walls of the CCV. The droplets of mist coalesce
into a liquid and drain back into the oil pan along with the oil that drives the turbine.
The gases are free to leave via an open port.
The open port connects to a tube leading to the bottom of the engine where road
draft draws the gases into the atmosphere.