Air filters are produced with either resin impregnated cellulose or synthetic polyester filter media, in either plastisol (rubber) or metal end construction, as well as the latest type, metal-free air intake filters. Oil separators for vacuum packages are constructed similar to that of the standard oil separators used in air compressors, and thus, will offer the same type of oil removal performance (in the range of 1–3 ppm / 1–3 mg/ m3). However, such separators are designed exclusively for flow direction the outside to the inside of the separator, and are suitable only to a maximum pressure differential (collapse point) of 22 psi / 1.5 bar.