What is PCV valve?

Answer 1

A PCV valve is a valve (or fixed orifice metering device) which adjusts airflow through the PCV system to allow PCV operation without adversely affection fuel metering. The PCV system moves air from the air cleaner through the crankcase, then into the engine intake. The function of the PCV system is to mix fresh air with contaminated air in the crankcase (contaminated by blowby gasses as partially burned exhaust slips past the piston rings) to then burn off the contaminants during normal combustion inside the engine. The purpose of the PCV system is to protect the oil from degradation, sludging, and acidity caused by exposure to blowby gases without venting it to the atmosphere (polluting.)

Such damage to the engine oil would tend to shorten engine life.