The working principle of an oil expeller is based on gradual pressure build-up inside the pressing chamber.

Oilseeds are fed into the hopper and pushed forward by a rotating screw (worm shaft). As the seeds move ahead, pressure increases. Oil is squeezed out through small gaps in the cage bars, while the solid oil cake exits from the end of the chamber.

In real oil mill operations, a properly designed oil expeller ensures smooth oil flow, stable pressure, and reduced wear on machine parts. This directly affects productivity and maintenance cost.