Positive Crankcase Ventilation (PCV) is an automotive emissions systems that's designed to direct combustion chamber gases that enter the crankcase into the intake stream to be re-burned in the combustion chamber. Polyvinyl Chloride (PVC) is a type of plastic polymer that's used to create industrial and consumer products. If you found this page by searching for "PVC" or "PVC valve" you probably meant to be searching for "PCV".