What does a PCV valve do?
When the engine is running, the combustion that occurs in the engine combustion chamber is not always perfect and not entirely wasted to the exhaust manifold. The exhaust gas that does not burn and does not get pushed into the exhaust manifold will circulate in the engine.
The gas circulating inside the engine is often known as Blow-by gas. Blow-by gas contains the active substance Hydro Carbon which will become dangerous pollution if inhaled by humans.
Therefore, most car manufacturers try to suppress and reduce Blow-by gas by adding a PCV (Positive Crankcase Ventilation) Valve component to the engine.
I. What is the PCV valve function?
As already explained above, the PCV Valve function is to suppress and reduce the amount of Blow-by gas in the engine due to incomplete combustion, especially Hydro Carbon.
The working principle of the PCV (Positive Crankcase Ventilation) Valve is to let Blow-by gas in the engine room back into the engine combustion chamber through the intake manifold.
Utilizing the air pressure from inside the engine room and assisted by the intake manifold vacuum, Blow-by gas is sucked into the engine combustion chamber to be burned back. That way, the amount of Hydro Carbon in the engine will decrease.
PCV Valve is usually placed in the Rocker Cover area and connected to the intake manifold. The shape of the PCV Valve can be different but have the same general working principles.
How does a PCV valve work?
To compensate and not interfere with engine performance due to outside air entering directly into the intake manifold, the PCV Valve work also follows the conditions when the engine is running. Among them is when the engine at idle, acceleration, or during deceleration.
What is regulated by the PCV Valve is a large amount of air flowed from the engine (rocker cover side) to the intake manifold. Here are the engine load conditions and how the PCV Valve works
1. When the engine is idling (high vacuum in the intake manifold)
When the engine is idling, the vacuum inside the intake manifold is high. The idling position stands for the throttle valve plate to fully close, so the intake manifold's vacuum load is high.
When the intake manifold's vacuum load is high, the valve (plunger) in the PCV will be sucked towards the intake and press the spring. The spring is in its shortest length but still leaves room for Blow-by gas to flow.
At this time, the amount of gas flowing from the Rocker Cover to the intake manifold is small. See the image below.
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2. When the engine accelerates (low vacuum in the intake manifold)
When the engine is accelerating, the vacuum level in the intake manifold is low. Accelerating stands for the throttle valve plate to fully open, so the intake manifold's vacuum load is low.
When the intake manifold's vacuum load is low, the valve position will be more open than when the engine is idling due to pressure from the springs.
The number of Blow-by gas that flows also increases according to the engine's conditions and needs. The following image is the condition of the PCV Valve when the engine is accelerating.
The Blow-by gas amount that flows from rocker cover to intake manifold will be the same.
3. When deceleration or excessive boost occurs in the intake
When the engine decelerates (decreases in engine speed), the throttle valve will typically close. It causes the air pressure in the intake manifold to increase.
At this time, the valve inside the PCV will close the Blow-by gas flow due to spring pressure and air pressure from the intake. Pay attention to the valve position in the following image.
When the valve is close, the Blow-by gas inside the engine (from the rocker cover side) will stop so there are no flows to the intake manifold.