Crankcase Ventilation System

A crankcase ventilation system, or CVS, removes unwanted gases from the crankcase of an internal combustion engine, typically using a tube, a one-way valve and a vacuum source such as the intake manifold. Rather than venting these blow-by gases straight to the atmosphere, as older engines did, the system recirculates them back into the combustion chamber to be burned along with the intake fuel and air charge, cutting the hydrocarbon emissions that atmospheric venting would otherwise release. Positive crankcase ventilation was the first implementation of a vehicle emissions control device, mandated in California starting with the 1961 model year, and the underlying approach evolved directly out of the earlier practice of simply venting crankcase gases to open air.