Positive Crankcase Ventilation: Description and Operation

The crankcase emission controls prevent crankcase gases from being released into the atmosphere. Instead, the gases are routed to the intake manifold. Crankcase gases are removed from the crankcase by positive crankcase ventilation (PCV). Intake manifold vacuum draws the crankcase gases out of the crank housing into the intake air stream, where they get ignited in the combustion process.

Fig. 43 Positive Crankcase Ventilation:

The fumes are extracted by routing them from the crankcase (outlet located center back of engine) to the oil trap where the heavy oil separates from the lighter vapors. The heavy oil gets routed back into the crankcase. The light fumes get drawn through the "anti backfire valve" to the air intake runner via the oil trap breather line. At the air intake runner connection there is an orifice installed to regulate the vacuum flow, Fig. 43.
To ventilate the oil tank, an oil tank breather hose is installed between the oil filler tube and the oil trap breather line.




COMPONENTS:

OIL TRAP
The air runner vacuum draws the crankcase fumes into the oil trap. The trap uses a baffle system to separate the heavy oil particles from the vapors. The oil runs back into the crankcase through the bottom exit. The vapors exit at the top of the oil trap.

ANTI BACKFIRE VALVE
The anti backfire valve is used to keep boost pressure, backfire flames and sparks from entering the PCV system.

ORIFICE
The orifice in the intake runner is calibrated to allow the correct amount of vapors to enter the intake air stream.