Positive crankcase ventilation system — description
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The positive crankcase ventilation system returns crankcase gases to the top of the intake manifold.
To remove crankcase gases to the upper part of the intake manifold, a forced crankcase ventilation valve is provided (PCV). When the engine is running at part-throttle, crankcase gases are sucked into the top of the intake manifold through the PCV valve. As a rule, the valve capacity is sufficient to remove crankcase gases and a small amount of ventilation air. The vent air is then sucked into the crankcase through a line connecting the air filter to the valve cover. When the engine is running at wide open throttle, there is not enough vacuum at the top of the manifold to draw blow-by gases through the valve and the gases flow through the hose connection in the opposite direction.
On vehicles with excessive amounts of crankcase gases, the valve will not be able to vent completely because some of the flow will go through the hose connection to the air filter under all operating conditions.