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The Emission Control System:
Positive Crankcase Ventilation (PCV)
During the combustion process, a great deal of force is created on top of the piston as expanding gases force the piston down. Piston rings are designed to create an effective barrier between the cylinder and the crankcase below.  However, the intense forces involved can sometimes cause a small amount of combusted fuel to slip by the piston rings and enter the crankcase. If left alone, the build up of gases in the crankcase could damage the engine, so traditionally those fumes were allowed to vent into the atmosphere.
However, venting a toxic mixture of sulfur, acid, particulate matter and unburned fuel directly into the atmosphere contributes to increased levels of pollution. Searching for a solution, engineers developed the Positive Crankcase Ventilation (PCV) system to both relieve crankcase gases and reduce emissions by simply recycling the fumes.
 Here’s how: First, the areas where toxic emissions used to escape into the atmosphere had to be sealed. That basically means, any place that has access to the crankcase, like the oil filler cap and the oil dipstick. Next, a ventilation system had to be installed that would allow fumes to be drawn out of the crankcase when the engine was running, strain out particles, mix the fumes with the right amount of fresh air and send it back into the combustion chamber.
 Next, a hose is connected to the intake manifold with the other end of the tube connected to the crankcase. When the engine starts running, a vacuum is created in the intake manifold that sucks fumes out of the crankcase, through the air cleaner, before being mixed and burned inside the engine.
The PCV valve is a one-way valve that regulates the flow rate of fumes out of the crankcase based on how hard the engine is working.  When the engine is idling, the plunger allows only a small amount of fumes to be drawn into the intake manifold. At slower speeds the valve opens a little more and during rapid acceleration the valve opens wide and allows for gases to be pulled through at a higher rate. When the engine is turned off the plunger closes the valve and does not permit fumes to escape. |
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Article Pages
1. Emission Control
2. Types Of Pollutants Created By Your Engine
3. 6 Ways In Which Emissions Are Reduced
4. Exhaust Gas Recirculation (EGR)
5. Air Injection And Catalytic Converter
6. Evaporation Emissions Control Systems (EVAP)
8. Automotive Emissions Wrap Up
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