Typical Twin Screw Air Compressors
3 = Suction (Inlet Valve is located)
2 = Female Screw (Usually driven)
1 = Male Screw ( Usually Driver)
4 = Discharge port (Outlet)
The position of the dark strip of Compressed Air, as it moves inward (lower side of screws assembly and the housing) to the other end, push in by the male screw (Piston) along the female flutes (cylinders).