Air oil separators remove compressor lubricant from the compressed air stream. The compressor lubricant is returned to the oil sump and the compressed air continues to the air receiver. 

A typical oil separator reduces the lubricant entrained in the compressed air to 2-3 ppm. Under normal operating conditions an oil separators service life is 4,000 to 6,000 operating hours. Air/oil separators are also called oil separators and demisters.