What is the Crankcase Ventilation System?

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Crankcase Ventilation System:

In an enclosed combustion engine, a crankcase mechanical system removes unwanted gases from the crankcase. The system usually consists of a tube, a one-way valve, and a vacuum source (such because the intake manifold).

The unwanted gases, called “blow-by”, are gases from the combustion chamber which have leaked and tolerated the piston rings. Early engines released these gases to the atmosphere just by them leaking through the crankcase seals. The primary specific crankcase ventilating system was the road draught tube, which used a partial vacuum to draw the gases through a tube and release them to the atmosphere. Positive crankcase ventilation (PCV) systems— first utilized in the 1960s and present on latest engines— send the crankcase gases back to the combustion chamber, to scale back pollution.

Two-stroke engines with a crankcase compression design don’t need a crankcase ventilating system, because the conventional operation of the engine involves sending the crankcase gases to the combustion chamber.


Source of crankcase gases:

Blow-by, because it is commonly called, is that the results of combustion material from the combustion chamber “blowing” past the piston rings and into the crankcase. These blow-by gases, if not ventilated, inevitably condense and mix with the oil vapor present within the crankcase, forming sludge or causing the oil to become diluted with unburnt fuel. Excessive crankcase pressure can furthermore cause engine oil leaks past the crankshaft seals and other engine seals and gaskets. Therefore, it becomes imperative that a crankcase ventilating system be used.



Two-stroke engines which use crankcase compression don’t require a crankcase mechanical system, since all of the gases within the crankcase are then fed into the combustion chamber. Many small four-stroke engines like lawnmower engines and electricity generators simply use a draught tube connected to the intake system.

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