Positive Crankcase Ventilation: Description and Operation
Positive Crankcase VentilationPipe A.
the PCV valve in the valve cover has Pipe A connecting it to the intake manifold, this connection is downstream of the throttle valve (High vacuum area).
Pipe B.
Pipe B connects the valve cover to the intake system rubber bellows between the air cleaner and throttle body, this connection is upstream of the throttle valve. Pipe B has no restrictions and allows air to travel in both directions depending on the pressure in the crankcase.
Under normal driving conditions (negative crankcase pressure), air is drawn into the crankcase via pipe B and mixes with the blow by gases in the crankcase. the gases pass back up through the crankcase and re-enter the cylinder head cover. A negative pressure (vacuum) in the manifold will be sufficient to open the PCV valve and allow the gases to enter the inlet manifold downstream of the throttle valve through pipe A and be drawn into the combustion chambers.
When the engine speed is high (positive crankcase pressure), the volume of blow-by gases may be too great for the PCV valve to handle alone, vacuum in the inlet manifold will also be greatly reduced. Under these conditions the blow-by gases will also flow through pipe B and enter the air inlet system upstream of the throttle valve, where they will be drawn into the combustion chambers.