PCV valve definition
Part of the positive crankcase ventilation system , which reroutes crankcase blowby to the intake manifold and back to the engine, where it is reburned in the cylinders as part of the fuel-air mixture . This cuts emission pollution and improve fuel economy because unburned fuel in the blowby is consumed the second time around. It also keeps the blowby and water vapor from fouling the oil in the crankcase , thus reducing the formation of engine sludge .